Part 71- The Four Mauve Anchor Delaminations Betray The Four Layer Delaminations below Anuket

Your attention is drawn to the new “PARTS MENU (quick links)” in the menu bar above. It allows much quicker sequential-number access to the numbered parts than the year/month chronology that’s so favoured by blogging platforms. 


Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

The first header is photo 14  reproduced. The second header is unnumbered as it’s a reminder from Part 70 and will be inserted in a few places to save scrolling up and down to the top. Photo 14 is at the end of the post. It shows a summary of the various layer slides and delaminations laid out in this part and Parts 69 and 70. Photo 14 has a description which, along with other preceding photo keys, explains all the slide vectors in the first header. 

The other three header photos are designated as being photos 1 to 3. Photo 3’s description is divided into several paragraphs ending with ‘/////’.

It’s advisable to read Part 70 as a primer to this part because it shows two views of the four layers. It’s much shorter than usual, mostly photos. 

Your attention is also drawn to Appendix 2, which has a selection of photos showing how the four mauve delaminations each sit on their own respective delaminated layer. 

Photo 1

The four mauve dots in the third header are sitting on four similar shapes that once nested together. They have delaminated along with the onion layers they’re sitting on and they’ve delaminated along the long-axis direction of the comet which is consistent with the tensile forces of stretch. This is elaborated on further down. The delamination was rather like the opening up of one side of a cantilever tool box where the trays slide over each other (except the trays are filled to make them solid slabs or layers sliding over each other). We’re looking at four mauve features and each one sat on its own respective tray or layer, making four features on four layers. Each mauve feature is at the northern end of its respective layer and perched on the front lip of that layer. Each front lip is stepped up above the next layer and not very obviously so in the case of the farthest two layers towards Hathor. Each layer is deeper as we progress from the one nearest us, and towards the Hathor cliff (from layer #4 to layer #1 in photo 2). The features are dotted mauve because they were all once nested to the classic mauve anchor (Part 24) which is the third feature on the third layer per photo 2. 

Photo 2

This is a close up of the photo above. It shows the exact outlines of the four mauve features and numbers them, #1 to #4, from the Hathor cliff end back towards us. The classic mauve anchor from Part 24 is #3. The blocky rectangle from Part 50 is #4. If you’ve been reading the blog, these features will be familiar and things will make sense more readily. The #1 and #2 mauve features will get their own names in due course because they’ll be referred to a lot for several more parts. Their northern perimeters (left hand perimeters in photo 2) define where the Aswan layers were originally attached before they slid across Hapi (Part 47). 

In summarising photos 1 and 2, we have four layers enclosing three delaminations: #2 from #1; #3 from #2; #4 from #3.

The four layers, #1 to #4 shouldn’t be confused with ‘levels 1 to 3’ in Part 39. Those three levels ran along Babi and Aswan. The four delaminated layers in this part are a different set of delaminations subject to wholly different shear force and tensile force vectors. This different force vector set-up is by virtue of their being inside the red triangle, or rather, inside the newly extended red triangle presented further below. 

Photo 3

This shows the four delaminations in close-up. It also shows the 1.6km x 200m rift in red (Parts 48 and 49). This rift is key to understanding the shear forces and tensile forces of stretch that caused the mauve delaminations.

Light blue denotes the so-called fracture plane which is in Part 26, signature 2. The fracture plane is now known to comprise exactly one of the delaminations, layer #2, and hosts the #2 mauve feature perched on its front lip, towards the #1 delamination. Its length and width are indicative of the other similarly sized delaminations either side of it which are less obvious until you use this shape as a guide. The fracture plane is therefore the area of one cantilever tool box tray. In reality of course, the layer containing the exposed delamination (fracture plane) extends beneath the other layer towards us i.e. under layer #3 that hosts mauve feature #3 and possibly under layer #4 as well. That’s where the toolbox analogy breaks down, unless it’s conceived as having very wide trays with the exposed delaminations being the first open apertures of each tray appearing. 

The four dots, mauve, yellow, orange and dark green are the four coloured anchors first presented in Part 24. Mauve yellow and orange sit along the front lip of the #3 layer. Dark green sits on the #2 layer. 

If you’re schooled in the Part 24 narrative, it will come as a surprise that the dark green anchor isn’t on the same layer as the other three because the head lobe shear line is supposed to run through all four. It does run through all four but the simple fact is that orange delaminated from dark green while the head lobe was still attached to the body. This happened as the #3 layer delaminated from the #2 layer. This delamination of orange from dark green was tweeted with photos long ago but is still awaiting its own blog post. The mirror image of the body delamination is even discernible on the head rim underside. They’re both in the same tweet:

WordPress has reproduced this as a tweet stream (with missing tweets) instead of just the link I typed so apologies to Dr. Nick Attree for being dragged in to this blog post. You can click on it to see the relevant tweet he’s quoting. The photos and their originals (which are more compelling) are reproduced at the bottom as a mini-appendix. 

As if this isn’t enough proof, this same delamination is betrayed even on the upper side of the head rim, that is, the flared, upper side of the rim at Serqet. It’s the two curved, blue ridges in Part 24. Those two ridges are situated directly on the other side of the rim from the ‘underside’ tweet photo. They used to be nested. 67P simply couldn’t be trying any harder to let us know it stretched. 

The tweet photos prove that the dark green-to-orange delamination took place before the head lobe actually lifted off the body. The head had to be clamped to the body for them to exhibit the same mirrored features let alone the same sliding signature. And since the head must therefore have been attached to the body during the delamination, and it also involves a whole layer delaminating by 300 metres along the comet’s long axis, it represents ongoing stretch of the single body due to spin-up. That would therefore be proof of 67P stretching even before the head sheared. 

The reason this delamination can be extrapolated to a whole layer is because the mauve and yellow anchors moved back on the same front lip of the layer with the orange anchor. That brings us back to where we were: the #3 layer delaminated from the #2 layer, taking the mauve, yellow and orange anchors with it. Meanwhile, the green anchor remained on the #2 layer as the vestige of the progenitor to the orange anchor. Much more evidence of stretch before head lobe shear is available in Parts 26 to 29. 



Photo 4- this is photo 2 reproduced

Below is a description of the mauve delaminations. More photos follow, further down. 

This part is important in its own right but it’s also placed here in preparation for explaining the Aswan/Hapi layer slides. Those slides happened right next door to the line of mauve delaminations in this part. They went off in a different direction. This part and the next few parts will explain why the mauve delaminations behaved so differently from the Aswan/Babi slides even though all the layers concerned were joined together before they were torn apart, slid and delaminated. They were joined as continuous layers running across that very straight line we see running down the northern side of the mauve delaminations. That would be the straight line kissing this side of all four mauve features in the header photos. It is the southern perimeter of the 1.6km x 200m rift. 

So far, only one of the Aswan/Babi slides has been explained. It was the Aswan layer slide in Part 69. The southern perimeter of the 1.6 km x 200m rift is crucial to understanding why the Aswan layer and the one below it broke away from where they did and why they slid in the direction they did. They broke away from the southern rift perimeter line and went in one particular direction, 90°, from it. Meanwhile the four mauve delaminations shown in the headers slid along the other side of the southern perimeter. They slid along it, kissing it all the way, and didn’t move away from it at 90° at all. This is completely different behaviour for the two sections of crust that were once joined and then momentarily kissing each other on being sheared from each other. This seemingly bizarre behaviour is easily explained when viewed from the perspective of a stretching comet as will be gradually laid out in this part and the ones following it.

The 1.6 km x 200m rift was annotated in part 69 and invoked for explaining the main Aswan terrace slide. However, the exact mechanism for how the rift sheared along today’s southern perimeter and opened up has not been fully explained before, not even in Parts 48/49. This also implies that Part 69 isn’t the whole story and that the supposedly immobile, lower layer in that part also slid from the southern rift perimeter. It will be shown to have done so in a future part but you don’t have to wait for that part. All the matches are there, it just requires looking at a few photos from different angles to see them. The photos are all in Part 69 and this part. 

It has been hinted at before that the southern rift perimeter line was very important and that the comet’s morphology differs greatly on either side of it but this part starts to unravel why the line is such a strong demarcation line between two distinct areas. It won’t be the full explanation but the photos below make a start in showing how the mauve delaminations were concertinaed out along this line, hugging it all the way. 

The fact that the mauve delaminations extend right into Hapi from the classic mauve anchor (Part 24) means that we can now extend the northern long side of the red triangle as far as the furthest delamination (#1). That’s almost as far as the Hathor cliff. It also implies that the other long side of the red triangle, the southern side can be extended in a similar manner. The northern extension is shown in photo 5, below, and it shows the southern extension in the background. 

Photo 5- the red triangle extensions with original
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

The northern long side of the original red triangle is shown running from the sharp, red triangle tip at bottom-right, up to the mauve anchor. The southern long side also runs from the sharp tip and runs to the dark green anchor. The base of this original triangle, also drawn in red, is between the mauve and dark green dots. The new extensions run on past both the mauve and dark green dots. On the mauve side, the extension to the northern long side kisses all four mauve delamination features as it descends into Hapi and ends at a location that’s in line with the strangely squared-off northern end of the Anuket neck. Much the same thing happens for the southern extension but that’s beyond the scope of this post. If we were to join the two ends of the two extensions (not shown) this would be the new, larger red triangle base. It runs under Anuket and along the front lip of layer #1. Thus, the new triangle’s footprint takes in most of the footprint of the Anuket neck’s base. This should come as no surprise for anyone who’s read Part 57. Layer #1 is where the large, flat expanse of Serqet used to sit before tipping up to its current, more vertical position. It tipped up because it was herniating prematurely and through the layer above. That’s why it’s dubbed ‘the vertical wall’ in part 26. Serqet extruded the Anuket neck from the body after the head sheared and rose on the stretching neck. Layer #1 is therefore the base of the Anuket neck by definition. This was even stated as far back as Part 25 (the three-sided box shaping the squared-off form of the Anuket neck through having material extruded from it and through it).

The southern extension doesn’t need to rely on any supposed symmetry with the northern extension to be invoked. It was already implied in Part 57 but wasn’t explicitly pointed out because the northern extension is more obvious and should be aired first. But the southern extension is symmetrical with its northern twin, just like the rest of the isosceles triangle (the red triangle) that the two lines extend from. This is owing to the fact that both the red triangle and its two extensions are straddling the paleo rotation plane (see the ‘Paleo Rotation Plane Adjustment’ page in the menu bar). The paleo rotation plane caused this symmetry when 67P was stretching as a single body. This was before the head lobe sheared and rose on the stretching neck. It’s explained in the page cited above and in Part 26. 

The southern red triangle extension line exhibits the same layer delaminations as the ones on which the northern, mauve delaminations sit. In other words, those delaminated layers are strips that run across Hapi or Seth. They run in front of Anuket but in the case of layer #1, its middle section is largely hidden under Anuket. The delaminated layers, #1 to #4, therefore kiss the red-dotted lines at each end. That’s where they were sheared at both ends by the shear gradient running down either long side of the red triangle (Part 26 and upcoming parts). All crust layers outside these two lines were also sheared, by definition, and recoiled from the lines. In the case of the northern line, it was the 1.6km x 200m rift in Parts 48/49. In the the case of the southern line, it was layers at Anubis that recoiled from that exact line (translationally matched to the line in Part 54). Put another way, the flat expanse of Anubis is another large rift. Specifically, it’s the floor of a much wider rift than the 1.6km x 200m rift. This hasn’t been mentioned before and will get its own full post in the future. The northern and southern red lines are of course the long sides of the red triangle including its new extensions. 

One of the delaminations runs directly in front of the neck in Hapi (the so-called fracture plane, signature 2 in Part 26). This is layer #2 containing mauve feature #2 on its front lip. And a narrow part of the width of the next layer down, layer #1 is also visible across the front of the base of the Anuket neck but, as mentioned above, a large part of its central portion goes under the neck leaving its full 300-metre width visible only at either end. 

It should be mentioned that there is also a supposed layer #0 beyond layer #1. That’s beyond the scope of this post and will be presented later. It’s inferred rather than self-evident and that inference is via the four clear delaminations we see in the headers. Its importance arises from the fact that it runs entirely under the neck behind Anuket and is probably not actually a layer but unlayered (or less obviously layered) core matrix material. It probably therefore also contributed material to the Anuket neck along with layer #1.

All of the four delaminated layers are about 800 metres to a kilometre long and about 300 metres wide. They are successively longer as we move from layer #4, the shortest, to layer #1, the longest. This is owing to them fitting into and across an ever-widening triangle as they progress towards its base along the front lip of layer #1. The layer widths are determined by the distance between the mauve-dotted delaminations shown in this part because each mauve feature sits on the front lip of its respective layer. But the so-called “fracture plane” (layer #2) presents itself in its entirety as being about 800m by 300m and it also contains the #2 delaminated mauve feature. It was called a fracture plane because it wasn’t recognised as a delamination in Part 26. It was only recognised as the top of a deeper layer than the coloured anchors’ layer (#3) and it was assumed the layer above it had cleaved away cleanly from it and in doing so, sheared along the line of the coloured anchors. Instead, the layer above slid away across it. That was the #3 layer. #3 is the one with three of the four coloured anchors: mauve, yellow and orange. This means the layer with the anchors delaminated from the fracture plane around the time of head shear. They delaminated while being integral to the front lip of layer #3 and did so from where they had sat along and on top of the the front lip of layer #2, the fracture plane. So the two lips were set one above the other as you’d expect them to be before the delamination occurred. 

So the mauve, yellow and orange anchors used to sit along the front lip of the fracture plane. They delaminated from it on their own layer, layer #3 and are now 300 metres set back from that front lip of layer #2, the fracture plane. There are additional translational matches across this 300-metre width for the yellow and orange anchors as well as mauve, which prove this. 

Moreover, the very flared-out rim of the lowest Serqet layer (i.e. the head lobe rim above the anchors) fits to the fracture plane directly below it. It’s part of the same layer that the mauve, yellow and orange anchors are a part of (layer #3). It was married up to the four anchors when the head was clamped to the body and still stretching. That’s why it’s so flared out- it’s one of the most stretched parts of the comet. It’s also why the head-body matches in Part 24 are so faithful. They match the flared rim to the anchors as well as the apparently softer material between them. It’s a 1km-long continuous match. 

The green anchor remained on layer #2 while layer #3 delaminated from layer #2 along with the other three anchors. However, the same scenario applies to the green anchor and head rim above it albeit with the Serqet rim being stretched down more than flaring out (Part 27). This was due to the lack of horizontal movement of the dark green anchor in contrast to the mauve, yellow and orange anchors sliding on layer #3 and giving rise to the flared head rim just before the head sheared. 

The four mauve features are denoted mauve because they were all originally nested under or over the mauve anchor, which is the mauve feature #3 on layer #3. Features #1 and #2 were nested under it and #4, the blocky rectangle, was notionally nested over it but in practice it was attached to the back of it (see subsequent photos and the Part 50 header). The slide of the mauve, yellow and orange anchors within their layer and across the 300-metre-wide fracture plane is in keeping with the well-documented red triangle recoil (signature 5 in Part 26) which was the next delamination back towards Apis. The red triangle recoil was the last delamination i.e. layer #4 from layer #3. 

It has to be remembered that these ~800m-long, 300m-wide strips are simply the visible parts of the now-exposed, delaminated layers. Each layer carries on under the higher-numbered layer that slid back across it. Presumably, they extend under for quite a long way. 

The layer delaminations along the southern perimeter of the red triangle are slightly less obvious but clear once you’ve checked the dots and then gone to the original to trace the line for yourself. Perhaps the most obvious southern extension delamination is the second one, which is the one in the tweet linked above. It shows the green-to-orange delamination which is layer #3 delaminating from layer #2. The third delamination is pretty evident as well. That’s in photo 9, below. It’s the ‘red triangle recoil’ from Part 26. It shows layer #4 delaminating from layer #3. So we have four layers enclosing three delaminations: #2 from #1; #3 from #2; #4 from #3. This means there are three strips or cantilever tool box trays, each one representing a delamination. 

Since the three delaminations of the four layers are bounded by very straight extensions of the straight red triangle sides, it means the triangle has grown beyond its former base along which the four anchors are spread (Part 24). The sides are now longer and the base is wider. Since it’s an extension of the original triangle and bigger, it’s ‘similar’ per the strict geometrical definition of similar which means the same shape of triangle with the same proportions and angles but of a different size. The classic red triangle is isosceles in nature and nested inside its larger, new-found companion which is of course, also isosceles. So the sharp end towards Apis is common to both triangles. And since the triangle owes its existence to spin-up and stretch, it’s aligned exactly along the long axis. Its line of symmetry is running down the middle and that line is contiguous with the paleo equator which is the paleo rotation plane. The sharp vertex is therefore on the paleo equator and the base of the triangle is bisected by it.

The extended red triangle’s base extends under the Anuket neck. In fact, the base encloses about half of the Anuket neck’s footprint on the notional Hapi plane that extends under Anuket. This is hugely significant for anyone who’s read Part 57 (also Part 25). Anuket was extruded out of the body through this area by Serqet as Serqet lifted from the body, specifically, by the sliced vertical wall layer that’s now a part of Serqet along with the flared rim layer. The vertical wall was probably only able to do this because the mauve delaminations described in this part slid back to reveal much deeper material. This would be non-layered core material or less obviously layered core material that was either three or four layer thicknesses deep. Layer #1’s surface is three layer thicknesses down. Layer “0’s” surface, beyond layer #1 and beyond our triangle (for now), is four layers down and appears to be possible core material. That’s why the Anuket neck looks so different from Hathor and Sobek next door on either side. They were cleaved, Anuket was extruded because it’s at the back of the neck with respect to the long axis and the rotation plane. Thus, it couldn’t avail itself of the cleaving process and was unceremoniously wrenched out of the body. This is why large chunks of icy material are falling from the join between Anuket and Hathor. They’re coming from the Anuket side of the join because they were yanked out from the core. 

Photo 6- Simple close up of the four mauve features.
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER
Photo 7- A more detailed close up. ‘Original’ from part 25.
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

Mauve- the delaminated features.

Light blue- the so-called ‘fracture plane’ which is delaminated layer #2 containing mauve feature #2.

Larger mauve dot plus yellow, orange and dark green- the four coloured anchors from Part 24. 

Photo 8- Same as photo 7 but with the 1.6 km x 200m rift shown in red. 
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

Red- this is not the whole rift. Roughly half of it is off-screen to the right, towards Apis. The upper line, kissing the four mauve features is both the southern rift perimeter and the northern perimeter of the red triangle. The red triangle’s northern long side used to extend as far as the larger mauve dot (the mauve anchor and feature #3) and its base was then formed by drawing a line from the mauve dot to the dark green dot. 

Strictly speaking, the old triangle base goes all the way along the front lip of layer #3 without jumping across layer 2 to the green anchor. However, when the red triangle was first presented, it wasn’t known that orange and green sat on different delaminated layers so the shear line was assumed to be one delaminated layer lip, not jumping across layers to green at the last moment, near the southern long side of the triangle. It was known to look slightly awkward but put down to the vicissitudes of uneven surfaces. However, 67P is continually showing up even these tiny apparent excursions as having an explanation via the tensile forces of stretch, in this case, the #3 from #2 delamination. Another one is the messy-looking ‘tell-tale line’ (Part 25) at the green anchor that spreads out like a river delta. It’s now been matched to the shape of the green anchor (which has existing matches either side of the delta) and it was matched only a few days ago, bringing eighteen months of head-scratching to an end (see part 70, photos 5/6). 

The new delaminations presented here are #2 from #1 and #3 from #2. #4 from #3 was already known as the red triangle recoil in Part 26 (see photo 9, below). Because of the two extra delaminations, the northern long side of the triangle now extends a long way past the mauve dot and into Hapi. It extends to the edge of the frame as shown and then about five red dots off-frame before turning right to go along the new, larger triangle’s base. In doing so the base traces the far end of the #1 mauve feature before diving under the Anuket neck. And the far end of the #1 mauve feature is front lip of the #1 layer. In photo 8, the neck is that isolated feature at the top of the frame that looks like a gnarled tree trunk. It’s the northern end of the neck that looks very squared-off. It protrudes a bit into Hapi thus creating an alcove with the Hathor cliff whose base is at the very top of the frame, in shadow. 

Photo 9- The red triangle recoil from Part 26. This shows the matches betraying the delamination of the #4 layer from the #3 layer. 
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

This is a long, narrative key with some colour sections broken into paragraphs.

In photo 9, the front lip of the #3 layer is the head lobe shear line and therefore the #4 layer recoiled (delaminated) when the head sheared from the front lip of #3. The head lobe shear line curves across from layer #3 to layer #2, reaching the green anchor which is just off-screen to the right. It then continues on round the body from there (see Parts 17, 19, 30, 21, 2, 1, 3 which match the shear line in sequence all round the head/body and almost back to the mauve anchor). The crossover point from #2 to #3 is exactly at the orange dot where there’s a step-up that’s mirrored on the head rim. You can see this step-up in the tweet photos linked above. 

Red arrows- direction of the recoil (layer #4’s slide) directly away from the head lobe shear line (layer #3’s front lip) and towards the long-axis tip at Apis. The recoil distance is about 200 metres and in line with the 67P long axis as are the other delaminated layers’ slide vectors. This is a strong signature of stretch via spin-up being the cause of the delaminations. 

Mauve- this shows the face of the entire mauve anchor i.e. the section that clamped directly onto its head lobe match 1000 metres directly above. It’s a mirrored match. The mauve anchor is the #3 mauve feature in the header photos for this part. This shape and its head lobe match are shown together in close up in Part 24 (photos 17, 18 and 19). They of course look remarkably similar. Notice how in photo 9 the mauve dots go round three sides of a square, which is in profile to us. These three sides define the two sides of the match and the top between them. That would be in ‘upright duck mode’ with the dust of Hapi sitting below the match i.e. the open end of the square facing down to the dust. 

The three-sided square comprises the entire blocky massif that comprises the anchor itself. The classic mauve anchor location denoted by a single mauve dot is always at the centre of the top perimeter. There’s a reason the bottom side of the notional square isn’t marked. It’s because this photo is from Part 26 and at the time of writing that part, it was suspected but not known for sure that the mirrored match to the head rim ends across this line. The direct match does indeed end across this line. It can’t match any lower because the curved shadow below it is the seating for the blocky massif that’s off-frame to the right here. That massif is the #2 mauve feature and it’s shown in photos 10 and 11. In those two photos it will be shown to nest into this curved, shadowed area. 

There also appears to be a match on the head rim to the #2 mauve feature and not to its curved seating under the mauve match. That match is a continuation of the head rim’s direct match to the main body mauve anchor in this photo, photo 9. This proves the head rim sheared from the mauve anchor on the body when the #2 feature was still nested at the mauve anchor (#3). Otherwise the #2 feature couldn’t match to the head rim where it does.

In part 24 photos 17, 18 and 19, the shadowed curve was the one actually matched to the head rim instead of the #2 mauve feature. This is because it looked remarkably similar from that angle because the seating matches the mauve feature anyway. It was also due to not knowing that the #2 mauve feature nested here or even that layer #3 had delaminated from layer #2. However this extra match below the direct mauve match was dotted light yellow because it looked as if it was essentially a match but there was more to the story. The delaminated #2 mauve feature nesting in the shadowed curve is the rest of that story- another slight anomaly resolved by invoking the tensile force vectors of stretch. 

The shadowed curve is the line that’s dotted mauve in the close up photos above because that’s the exact nesting line on #3, the anchor, for #2 to nest to. 

Bright green- this annotation is bright green instead of mauve and red. It’s owing to the fact that this photo is from Part 26 when features spread along this line behind and in front of the mauve anchor were in bright green. This was in deference to the slab A extension perimeter line. That very straight line is exactly the same one as the southern rift perimeter which itself is the demarcation line for the slab A extension. They are one and the same. Thus these bright green annotations can be translated to the mauve/red language of this part as follows. The left hand bright green line is the front end of the blocky rectangle and so would be the #4 mauve feature in the header. As mentioned above, it notionally nested to to the mauve anchor but in practice it was clamped to the back of it. This seating for the blocky rectangle on the back of the mauve anchor is the middle bright green line. The seating hasn’t been pointed out or annotated in any colour in above photos. The right hand bright green line is just a small portion of the southern rift perimeter extending into Hapi and so is part of the red-dotted rift line in photos above. It should be said that the blocky rectangle line and its seating line are both a bit too long. The match has been refined since Part 26 (see Part 50). 

Larger yellow dot- the classic position of the pointed tip of the yellow anchor. This matches to the tip of the pointed head rim section above. That point on the head rim is the very obvious southern pillar of the C. Alexander Gate. The anchor on the body itself spreads either side of this dot as described in Part 24. 

Larger orange dots- the right hand one is the classic position of the orange anchor. It corresponds to the apex of a sharp, V-shaped dent in the head lobe rim above. The left hand one is the position of its slid match on the red triangle recoil layer which is the #4 layer for this part. So the right hand orange dot is on the front lip of layer #3 and the left hand one is on the front lip of layer #4.

Small yellow- the three concatenated curves running down from the larger yellow dot are sitting exactly on the head lobe shear line. The three-sided feature below the three curves and incorporating the orange dot is largely following the V-shaped match on the shear line but extends past the exact match at either open end. This feature marks the solid massif comprising the main body of the orange anchor. The isolated yellow curve to the right of the larger yellow dot marks the solid massif comprising the main body of the yellow anchor. Only its top edge follows the shear line. 

Very small yellow- mini matches that map over to very small red dots (see below). 

Red (large and small)- all these features match to their respective yellow matches along the shear line. They are a translational match, not a mirrored match as described for the case for the mauve anchor and its match. They are translational because they slid (recoiled), in the direction of the arrows, from their yellow matching features. The mauve match broke in two hence its mirrored character. 


Regarding the red triangle recoil, It’s interesting to recall that layer #3 delaminated from layer #2 while the head was still clamped to the body. We know this from the tweeted orange-from-green (#3 from #2) delamination which the head rim obeyed in lock step with the body. We also know this from the fact that the head rim matches to the coloured anchors on layer #2 (dark green) and layer #3 (mauve, yellow and orange). So the #3 from #2 delamination on the body dragged the yet-to-shear head with it because head and body were essentially a single stretching body at that time. But the #4 from #3 delamination (the red triangle recoil) was a genuine recoil when the head sheared. It didn’t drag head lobe layers across with it like #3 from #2 did. 

Of course, since #3 from #2 dragged future head layers with it then #2 from #1 absolutely had to do so as well. This is key to understanding the behaviour of the Serqet ‘vertical wall’ as it was herniating prior to head shear. It’s why it looks the way they do as described above (sheared by the red triangle extensions at either end; tip up along the front lip of layer #2 acting as a long hinge). Parts 57 and 29 provide much extra information and future parts will elaborate on this. 

And finally, for photo 9, the layer #2 from layer #1 delamination is why Serqet (and Nut) are constrained to be directly above and exactly within the extended red triangle sides i.e. the width of its new, extended base. That delamination caused slip shear by definition. The slip shear happened along the ends of the triangle long sides at either end of the new base, cutting the future vertical wall into a flat, rectangular tablet, one layer thick, which tipped up on herniation. The thickness of that layer is the width of Nut. The slip-shear event is the reason for saying “sheared by the red triangle extensions” above. 

Photo 10- A close up, viewed from above the head lobe. 

Yellow- these lines show various outlines of the head rim and the Anuket neck. The right hand one at a 45° angle is the actual head rim. The dark feature outlined in the middle is the obvious lump that can be seen in many photos, sticking out at the top of the neck. There’s a small, brighter part of neck beyond it and to the right. To the left of the lump, we see the Anuket neck running steeply down to Hapi. This section is in extreme profile from this viewpoint, looking down on the head lobe. 

Red- the 1.6km x 200m rift. The important southern rift perimeter is the one nearest to us. It’s the one kissing all the mauve features that delaminated from each other along it. Much of the rift is out of view at top left. This shows roughly half its length at most. The southern perimeter is shown dropping down into Hapi along the red triangle extension. In doing so, it runs down the centre of the mauve anchor and along a very straight line that continues out of view behind the head lobe. It kisses the shadowed curve mentioned in photo 9 and so this is the definitive #3 mauve feature to which #2 nests. The shadowed curve has been called the mauve anchor above because it is for all intents and purposes, the mauve anchor. It’s just that it doesn’t match directly to the head because the #2 feature matched to the head when it was seated in the shadowed curve. This was mentioned above. The area of the mauve anchor above the shadowed curve does match directly to the head so the very top rim of the cavern that forms the shadowed curve is the bottom perimeter of the mauve anchor. But the cavern itself isn’t a direct match to the head. 

You may recognise the track of this drop-down into Hapi of the red, southern perimeter. It looks similar to the bright green curve in Part 69. Strictly speaking, it’s not: it’s a straight line (when viewed from directly above) that runs down the centre of the mauve anchor. That bright green curve in Part 69 was representing the northern edge of the mauve anchor which is indeed curved. We are now in territory where the matches and mini-matches are highly nuanced. The shadowed curve, representing the #3 feature extends almost from the anchor centre line (the red line) to the southern perimeter of the mauve anchor and a little beyond it. Although the red line notionally represents the top of the mauve anchor as it passes it, it’s more to do with the fact that it defines the anchor’s central rib. The rib appears offset to the north of centre somewhat in this photo but it’s an optical illusion in this photo and photo 9. Photo 12 shows it as being central. 

Mauve- the four mauve features. They run from #4 at the top of the frame to #1 at the bottom. Only three are actually visible in this view: #2, #3 and #4. #1 at the bottom is denoted as a single dot where it would be if we could see through the head lobe to where it sits in Hapi. We can now see how feature #2 nests into the shadowed curve of #3 below the classic mauve anchor. The best ‘mini-match’ for them in this photo is the curved top of #2 that fits to the curved roof of the #3 cavern that causes the shadow of the eponymous shadowed curve. However, #2 has a triangular shape (very small mauve dots) and that is what fits to the actual recess of the cavern (dotted the same way in the recess shadow- for guidance, not very accurately). 

Photo 11- this shows #2 and its seating at #3 in the shadowed curve. 

From this angle both features look less curved, more angular. You can see how the seating at #3 uses the southern edge of the central rib (just to the left of the red line) as the northern perimeter of the seating line (mauve). The red line goes down the centre of the rib so the mauve seating line is the southern rib edge and the bright green curve of part 69 is the northern rib edge. The rib will become highly significant in the next few parts because it’s a very strong demarcation line between these mauve delaminations along it and the Hapi/Aswan slides away from it at 90°. It’s much straighter and more symmetrical when viewed from directly above than when viewed slightly from the side as in the last two photos.

Photos 12/13/14- context for photos 10 and 11. These are culled from Part 69 but have added annotations. Photo 14 is the main header for this part. Photo 13 is the same as 12 but with the mauve feature delamination vectors shown along with the rift/Aswan layer slide vectors. The vectors are the red arrows. 14 numbers the four mauve features that delaminated on the four layers.

Photos 12/13/14 show another view of the mauve delaminations. They’re a zoomed-out version of photo 11 in which you can see all four mauve features. Their mauve outlines are dotted with small mauve dots while the main mauve anchor (direct match to the head rim) has three larger dots denoting its top and southern side. These three dots betray the width of the rib that is itself dotted bright green. The smoothly curving bright green lines show how symmetrical the rib is. Again, you can see how it’s almost acting like a wedge between the mauve delaminations along it and the Aswan/Hapi slide away from it. Of course it never acted as an actual wedge- it’s the physical manifestation of the tensile and shear forces that gave rise to slip-shear and ultimately to those two different layer movement vectors. It’s the force vectors stamped on the comet for us to see and the two bright green ends are flared out because they were yanked in opposite directions along the shear line while the pointed part remained intact under the head lobe. More on that in ensuing parts. 


The rib is dotted bright green in photo 12 and not red because there’s a history of denoting this feature as a whole in bright green, dating right back to part 22, as well as noting its close relationship to a particular ridge on the head that’s also always marked bright green (since Part 24). 

Although the rib centreline defines the red triangle extension and so was dotted red in photos 10 and 11, that centreline also denotes the slab A extension perimeter from part 22. The two areas share this border precisely because it was such a strong tensile force line with such a steep shear gradient. The steep shear gradient was what made the line narrow. And the shear caused the 1.6km x 200m rift which means the southern perimeter of the rift is also contiguous with the red triangle and the slab A extension perimeters. That’s because the rift caused the divide between the two areas and their two distinct morphologies. The 200-metre rift floor is wholly within the slab A extension area and the mauve delaminations are wholly within the red triangle. The two morphologies are divided by this startlingly straight slip-shear line that’s no more than 20 metres in width. That’s the southern rift perimeter, including the bright green rib in photo 12. This is how we know the shear gradient was so steep across the line. The tensile force vector diminished suddenly across the 20-metre width and this diminishing set up the shear gradient which led to slip-shearing of the crust. The reason for the sudden diminishing of tensile force across the line was presented in Part 26 (red triangle likened to a wind-tail in the lee of a rock) but will be elaborated on in the next few parts. 

When we’re dwelling on the red triangle, as in this part, the rib centreline is marked red because it’s related to the vast area of the triangle behind it. If we’re dwelling on the slab A extension it has to be marked bright green in order to see its relationship to that area and to the ridge on the head directly above it. Since the Aswan/Hapi slides were entirely on the slab A extension side of the rib, it gets marked bright green for anything to do with the Aswan/Hapi slides. This is why the northern curved edge of the rib was marked bright green in Part 69. And it’s thus coloured in photos 12/13 because they are preview photos from a future part concerning the Aswan/Hapi slides. 

Since photos 12/13 are from a future part, you can see the bright green line extending further into Hapi beyond the #1 mauve feature and right up to the boulders. This is the line along which the Aswan layers were once attached as we’ll see in due course. 

APPENDIX- tweet photos and originals.

APPENDIX 2- various photos showing the four mauve delaminations on their respective delaminated layers. 

Photo A1

Small red- the layers, #1 to #4.

Large red- (in the second photo) the red triangle. Notice how it drops down into Hapi at the mauve anchor which is a dot that’s almost obscured by the red triangle dots. The red triangle line does a similar thing at the green anchor but with a small dog-leg round the solid, front corner of the anchor before the drop-down. 

Photo A2

Small red and large red- as for A1

Brown- a small portion of the paleo rotation plane (paleo equator). Notice how it runs straight through the sharp vertex of the red triangle and then across the centre of Apis at the long axis tip (bright green). It also bisects the red triangle longways as well as Anuket longways and Serqet widthways. This is because all these features were caused by the tensile forces and slip-shear forces of stretch via spin-up. That’s why they’re all symmetrical across the line that runs around the comet from long-axis tip to long-axis tip. That line is the paleo equator and the rotation plane that caused the stretching along the long-axis line.

Dark blue- a nearby portion of today’s equator/rotation plane for comparison. 

Bright green- Apis on the horizon. This is one flattened end of the highly symmetrical, diamond-shaped body. It’s centre is the exact long-axis tip of the comet.

In some photos in Part 70, the red-dotted layer lines traced their way round the shape of mauve features #1 and #2. However, this was for convenience to show where the mauve features were as they were somewhat whited out. The actual layer lips run across the front edges of these two mauve features i.e. the #1 layer lip and #1 mauve feature front edge are contiguous. And the same goes for #2. So the mauve features sit on their respective layers, not in front of them. This correct, straighter line for the layers is shown in the above photos and because of this, the mauve dots showing the delaminations sit directly behind the red lines. 

Photos A3 and A4 below are from Part 70 with the red layer lines going round the back of the mauve features #1 and #2. They’re reproduced here because the mauve features weren’t presented yet in Part 70 and so weren’t marked. So they’ve been added here to show again that there’s one delaminated mauve feature for each delaminated layer. The four mauve feature delaminations therefore serve to corroborate the four layer delaminations. This is because they’re more obvious in themselves than the layer delaminations as a whole and each one sits on a layer lip. This is the lead-in for looking for other translational matches between the layers. These matches are indeed there for all four layers and have been presented for #4 from #3 (red triangle recoil) and part of #3 from #2 (the tweet photos). Several more such translational matches exist, completing the matches between all four layers but these will be presented in a future post. 

But you don’t have to wait for those posts. All you have to do is look at enough close-up photos that include the layer front lips shown in this part and see the matches for yourself. Some of those matches are evident in the close ups in this part but weren’t noted because there’s enough evidence to prove the delaminations and its just too much discussion for one Part. 

Photo A3- This is photo 2 from Part 70 and one of the headers in this part. It has its key annotated on the frame itself. 

Photo A4- this is photo 6 from part 70.

Continuous mauve line- the classic mauve anchor (Part 24). This is the outline of the direct match to the head rim above. You can see that head match in this photo. Look for the mauve dot on the head rim and then trace the much smaller mauve dots either side of it to trace the same shape as on the body. The close up matches are in Part 24. 

Four separated-out mauve dots- these are the mauve feature delaminations, one for each layer delamination. each one is sitting on the front lip of its respective layer but #1 and #2 have the red layer line going round the back of them. It should really go across their fronts so that #1 and #2 are included on and within their respective #1 and #2 layers instead of sitting just in front of them. 

Yellow and green- annotations from Part 25. See that part for a full description but these two colours essentially trace the shear line where the head rim once sat. The continuous mauve line is also part of the shear line because of being a direct match to the head.  



Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

To view a copy of this licence please visit:

All dotted annotations by A. Cooper. 




Part 70- The Four Delaminated Layers Across the Width of Anuket.

Original- to track the lines without dots obscuring them:

Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER


Red- four delaminated layers sitting along the front of the Anuket neck. They’re the same width as Anuket. 

Mauve, yellow, orange- these depict the head lobe shear line. In other words, the continuous line drawn by these colours matches the shape of the head rim, 1000 metres above. This photo was culled from part 24 which explains these matches in great detail. Hence the ‘original’ still has the colours from that part. 

Photo 2- the layers, numbered, ready for Part 71 which will have a much fuller explanation. 

Photo 3- as photo 2 but with the red triangle sides (Part 26) added.

Large red- the red triangle (Part 26, signature 5). These are just the two long sides of what is a long, thin isosceles triangle. The sharp vertex is off-frame to the left. 

These two larger-red dotted lines look bumpy from this side view. From above they are both dead straight. This is because their straightness was brought about by the tensile forces of stretch. This was when 67P was stretching as a single body before the head sheared from the body. They are tensile force lines etched on the surface. 

Specifically, they are tensile force lines which had a steep shear gradient across their width (diminishing parallel tensile force vectors across a very narrow width of ~20 metres. This caused slip-shearing of the crust on either side. Hence these delaminated layers, #1 to #4, being perfectly enclosed within the two long sides and not encroaching past them to the areas beyond the triangle. 

The base of the triangle isn’t marked in large red here because it runs along the front lip of layer #3, which is essentially the head lobe shear line. The upper (northern) perimeter of the red triangle goes through the mauve dot and continues down into Hapi. In Part 26 it stopped at the mauve dot and turned to run along the base which was then the layer #3 front lip. 

Now that the layer #1 and #2 delaminations have been found it means the base of the red triangle runs along the front lip of layer #1 which means it runs under the Anuket neck. 

Photo 4- with mini-matches added in yellow. 

Yellow- These have been matched in other photos including in Part 26. However, the pair either side of the ‘2’ and the pair above it haven’t been mentioned on the blog before. They will eventually get the close-up treatment to prove these matches do exist in finer detail. 

Photo 5- a different view of the delaminated layers. 


Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

In photo 5, we can see the front lip of layer #1 which was in shadow in the above photos. We can also see the Anuket neck and how these four layers are arranged across its width which is highly significant (see Part 57, also Part 29). You can now see how the coloured dots and lines on the body match to the head rim (Part 24).

Photo 6- as for photo 5 but with the layers numbered in the same sequence as in the other view above. 

Notice how the head lobe shear line cuts across layer #2 as the former head rim seating curves round to match the path of today’s curving head rim. 


Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

To view a copy of this licence please visit:

All dotted annotations by A. Cooper. 

Part 69- The Entire Aswan Terrace Slid 200 Metres

Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

Green- the Aswan terrace cliff base (furthest away) and its original seating (nearest). The middle line is a line of boulders that also mirrors the shape of the cliff base. 

Mauve- a feature set into the cliff face and its seating nearer to us. 

Arrows- direction of the 200-metre slide. Note the small arrow off to the right on a nearby section that experienced the same degree of sliding. The arrow is smaller only because the head lobe is in the way. 


The header photos show the Aswan terrace, which is the main flat area. The front edge, nearest to the viewer, drops away in a cliff that’s about 100 metres or so high. It drops down to another remarkably flat terrace. That terrace is smaller and although it’s officially part of the Seth region, it looks rather as if it’s sitting in the Hapi region with Hapi dust skirting round its rectangular base. 

The bright green lines trace the bottom of the ~100 metre Aswan terrace cliff as well as its original seating along the front of the smaller terrace below. The cliff base slid 200 metres across the lower terrace. This means the entire Aswan terrace slid 200 metres because the cliff is the front edge of the terrace. The slide was brought about by the centrifugal forces induced by spin-up of the comet to a 2 to 3 hour rotation period. 

This should come as no surprise to regular readers. There are longer slides elsewhere on the comet and they involve larger slabs of the same thickness (e.g. Part 43, the ‘red slide’ at Imhotep). Moreover, Part 32 described the delamination of the main sink hole into the three holes we see today. The three holes are next door to this slide and they went in the same direction with a small radial difference in keeping with the radial nature of all the slides around the north pole (the radial pattern is shown in Part 37). 

This slide of the entire Aswan terrace layer is one layer lower than than the sink hole delamination. The two extra sink holes essentially slid (i.e. delaminated from the main hole) across the top of the Aswan terrace layer. That’s why the base of the second sink hole is at exactly the same level as the Aswan terrace. So it was the next layer up, sitting on the Aswan layer, that was clamped around the main sink hole, lost shear resistance at its base and slid back. The main Aswan layer in this part succumbed to the same loss of shear resistance. The loss of shear resistance was due to centrifugal forces. 

There’s an intermediate green line between the cliff base and its seating. That line traces a line of boulders. The boulder line mirrors the line of both the cliff base and its original seating. This phenomenon of leaving parallel lines of boulders in the wake of a slide is most obvious at Imhotep in one of the green slides. It’s shown in the Part 42 overview of Imhotep slides. The Imhotep green slides are not fully blogged yet. That Imhotep slide has left multiple lines of boulders that are parallel to the particular cliff base that slid. This suggests a stop-start component to the slide and supports Marco Parigi’s hypothesis that the spin-up of the comet is ‘pumped’ with several bouts of spin-up leading to several bouts of sliding along the same vector. Each time the slide starts anew, it involves a sudden loss of shear resistance at the base of the layer. The jerking motion as the layer sets off again is apt to dislodge boulders from the cliff face. The dislodged boulders of course trace the shape of the cliff base where they fall because that’s all they can do. This explains the green line of boulders in this part. They mirror the shape of the cliff base perfectly despite being 150 metres from it. Vincent et al. (2015) couldn’t explain this line of boulders as resulting from erosion of the Aswan cliff. This was because it seemed unlikely that these large boulders could travel over 100 metres from the cliff without breaking up. Link to the paper:

The full title of the paper is at the bottom of this post with the link repeated. 

There’s also a curved feature in the header, marked in mauve, along with its seating. It’s set into the cliff wall at its base. It’s fairly rectangular as well as being curved. It resembles a cave entrance or fireplace though in reality it probably has little depth into the cliff face. It will be referred to as ‘the fireplace’ at times in this post and in future. This blog is replete with “features” of all shapes and sizes but unless they have a pithy, unofficial name, it’s difficult to remind the reader 40 parts into the future. 

It’s difficult to tell how recessed the fireplace is but it certainly has some depth into the cliff. It’s rather dingy in that concave part of the cliff base, being in shadow, but this is one of the best photos for seeing into this recess. We can see that the curved base of the fireplace matches to the curve of its seating. 

Photo 2- Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

Mauve- fireplace.

Yellow- the crack, directly above the fireplace. 

The fireplace is sitting directly below a 80-metre crack that runs along the top of the Aswan terrace cliff. The crack is within the terrace dust and notionally parallel to the cliff edge, 10 metres from it and arced to the cliff edge at either end. It was noted in Vincent et al. (2015) and it was hypothesised that the 10-metre strip might crumble away as part of ongoing cliff erosion. It may well do so but its location directly above the fireplace, and being the same length, suggests a structural weakness running up the cliff that’s an extension of the fireplace structure. This, coupled with the stresses of a 200-metre slide across the lower terrace would very likely give rise to the 80-metre crack. I therefore hypothesise that this crack is yet another artefact of the stretching process, is a one-off structural failing and is not part of an ongoing erosion process brought about by sublimation.

It’s acknowledged here, as always, that sublimation is happening and leading to erosion to some very small extent. It isn’t responsible for the gaping chasms across the 67P landscape though. They were caused by delamination, rifting and sliding. 

Photo 3- fig 5B from Vincent et al. (2015) Copyright: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA/J.B. VINCENT ET AL. (2015)/A.COOPER

Red- the slide track of the fireplace from seating to its present day position. The track shunts left (as viewed when looking directly towards the cliff face). 

Yellow- the 80-metre crack sitting directly above the fireplace.

Bright green- As in the header (note the very end of the cliff base line peeping out of the shadow). The head lobe rim obscures part of the original seating line but it’s visible up to the central ‘nose’. 

You may notice that the mauve seating is closer to the central ‘nose’ of the cliff seating as compared with the actual fireplace and cliff nose that are further apart. This is explicable via tracing the path of the fireplace, which really means tracing the path of the section of cliff that contains the fireplace as it executed its 200-metre slide. There’s a track line joining the right hand end of the fireplace to the right hand end of its seating (from the viewpoint in the header, facing the cliff). These track lines have been documented elsewhere on this blog especially for the ‘orange slide’ at Imhotep (Parts 44 and 45). This particular track line takes a dive to the left at a certain point. 

The sideways shunt is in keeping with the long-axis stretch vector which is evidenced elsewhere along the Seth/Hapi rim (see next Part). The long-axis stretch has been documented in Parts 38-41 and various parts thereafter.

The stretching of the cliff itself might seem far-fetched but it will be seen in the next post that components nearby did indeed stretch along the long axis instead of undergoing the usual delaminating and rifting in response to the tensile forces of spin-up. 

Photo 4- Part 49’s 200m rift photo: (a) as originally shown without the Aswan slide (b) with the Aswan slide and slide vector arrows for the slide and rift (c) Unannotated original. 


Part 49 presented the evidence for the 1.6 km x 200m rift across Seth and Ash. The 200m slide of the entire Aswan terrace is really just the large section that had to slide in order to open up that rift. That’s why both the rift and the slide are about the same distance of 200 metres. The Aswan portion is a bit less in photo 4- perhaps it overhung the seating. More likely, it dragged the supposedly stationary layer below it just a tad. We’ll eventually come to see that this lower layer did indeed slide as well and has its own seating. 

So the Aswan slide is very closely related to the 1.6km x 200m rift. The additional information in this post is:

1) the areal extent of the slid layer on one side of the rift. That area is the main Aswan terrace. The sliding of the main Aswan terrace automatically implicates the wide, terraced cliff above the main terrace as sliding along with it.

2) the layer on which the Aswan terrace slid which is the small, lower terrace with the bright green lines on it. 

3) the thickness of the layer that slid as implied by (1) and (2) i.e. the thickness of the main Aswan terrace. 

4) the fireplace identification and the fact that it may inform the evolution of the crack directly above it. 

5) the jerk to the left of the fireplace slide, implying a stretching of the cliff face and, by extension, the actual terrace area (long-axis stretch in keeping with the Babi/Hapi delaminations in Parts 38 and 39). This is further evidenced by the fact that the bright green boulder line is offset slightly from the straight-line translational symmetry between the cliff base line and seating line in photo 4 and the previous photos. This implies a shunt to the right of the central ‘nose’ from its seating while the fireplace shunted to the left.

6) the deposition of the boulder line mirrors the cliff base line, which would be due, perhaps, to a stop-start sliding history. This implies a possible ‘pumped’ sliding and therefore intermittent spin-up to the rotation period necessary for shear resistance failure. 


Are fractured cliffs the source of cometary dust jets ? insights from OSIRIS/Rosetta at 67P 
JB Vincent et al. (2015)



Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

To view a copy of this licence please visit:

All dotted annotations by A. Cooper. 


Part 68- RA/Dec Anomaly in 67P Spin-axis Precession Papers


Key to the header photo which is not part of the numbered sequence:

The blue arrow is 67P’s spin axis

The short red line represents a circle which is at right angles to the pointed tip and so it’s at quite an oblique angle, hence being depicted here as a line just showing the diameter. The circle represents the approximate area that’s covered by the precession of the spin axis. So the point of the blue arrow precesses or rotates around and within this circle. The 225 data points in photo 1 are all squeezed into this red circle which is itself probably a bit bigger than the actual precession circle of around 0.5° diameter. The graph in photo 1 has stretched this circle into an ellipse. 


1) The photos

2) Introduction

3) The error

4) The Latitude/Longitude analogy

5) Applying the RA/Dec anomaly to 67P’s spin axis RA/Dec data

6) The relationship between figure 2 and the celestial sphere

7) The effects of the RA/Dec anomaly and why separated RA and Dec components show useful patterns

8) Information from Gutiérrez et al. (2016) that sheds more light on the RA/Dec anomaly

9) Three pieces of evidence for the RA/Dec anomaly

10) Calculations

11) Implications of the RA/Dec anomaly

12) Conclusion

This part isn’t designed to be read from start to finish if you have reasonable knowledge of the RA/Dec reference frame, precession/nutation and 67P in general. In fact, the first section, ‘The Photos’, should be enough. The rest of the sections are included for thoroughness and do include some useful extra analysis as to the reason the separated RA and Dec components of 67P’s spin axis show patterns, as well as implications for modelling the true circular precession pattern and ultimately, the inhomogeneity or otherwise of 67P. Sections 2 to 12 also include a more detailed explanation of what’s being described in the photos section. 

The most important sections are the odd-numbered ones as well as section 10. All the other even-numbered sections are generally weighted towards extra explanation for those not quite so well versed in the subject. That’s only a rough categorisation and there are useful snippets of information in the even sections too. 

Mathematical and physics terms/notations are repeated quite a lot as well as geometrical relationships and analogies. This is because a newcomer can’t be expected to remember all these things once, at the beginning, and juggle them all the way to the end. They’re repeated as gentle reminders at every stage so as not to sow confusion where one might be derailed by the subtler aspects of the arguments. 


Photos 1 to 9 follow, along with narrative captions. 

Photo 1- figure 2 from Gutiérrez et al. (2016). 

Credit: Gutiérrez et al. (2016)Astronomy and Astrophysics590, A46 (2016)DOI: 10.1051/0004-6361/201528029Copyright ESO 2016

This is an isotropic plot of the RA/Dec values for 67P’s spin axis that were measured over 125 days in late 2014. An isotropic plot is one which has units that are of the same size along the x axis as they are along the y axis. In this case the RA axis is the x axis and Dec is the y axis. They both exhibit degree units of the same size. This is the source of the error described in this part. The error is that the RA axis degree units should be 0.438 of the length of those on the Dec axis but they are of equal length. This causes the elliptical shape of the data that is really a circle in the real-world precession behaviour of the spin axis. The elliptical shape wasn’t amenable to modelling of the precession behaviour, presumably because it doesn’t represent the real-world, circular precession of the spin axis. 

Photo 2- figure 5 from Gutiérrez et al. (2016). 
Credit: Gutiérrez et al. (2016)Astronomy and Astrophysics590, A46 (2016)DOI: 10.1051/0004-6361/201528029Copyright ESO 2016

This is the attempted modelled fit to the elliptical data. It fits to the outside perimeter of the data points which is why Figure 5 is used for the calculations sections below. However, it has a hole in the middle which leads to difficulties filling it whilst constraining the inertia moments and excitation to reasonable values. The hole doesn’t affect the calculations below but the calculations will probably have an indirect effect on the hole by making the circularised data set easier to model. 

Photos 3 to 7- these show the celestial sphere in the Equatorial reference frame which is the RA/Dec reference frame. The right ascension (RA) lines are the longitude-type lines that join at the celestial north pole. They’re 15° apart. The declination (Dec) lines are 10° apart and are akin to latitude lines. The celestial reference frame can have its origin at the centre of the Earth (geocentre) or at the centre of gravity of 67P. The several-hundred-million km shift is immaterial since they’re both deemed to be in the same place as set against the quasi-infinite distance to the reference stars on the celestial sphere. 

Photo 3- this is from Wikipedia. It’s a portion of the celestial sphere where 67P spin axis points to, i.e. its spin pole coordinates. This is for general orientation and for referring back to. The spin pole isn’t marked in this photo.
Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg) Creative Commons Attribution 3

Photo 4- a close-up with the RA/Dec position of 67P’s spin pole, marked in orange. It’s in the middle, next to the alpha symbol. This is at RA, Dec = 69.57° , +64.01°, placed with an accuracy of about 0.5°. Each hour line of RA is 15° so 5hr is 75° hence the dot being 2/3 between 4hr and 5hr for 69.57°. In this case, the RA/Dec reference frame origin is at the centre of gravity of 67P.

Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)/A.COOPER
(same credit for photos 5 to 7 which are similar crops). 

Photo 5- this is closer still. The celestial pole is kept in view at top-left for orientation. You can always refer back to photos 3 and 4 as well for orientation. 
In photo 5, the mauve-dotted line shows a track of 10° as measured along the RA axis. This means the line is drawn along the Dec = +64.01° line. It straddles the 67P spin pole dot, so it runs 5° of RA either side. 

The fuchsia line shows a track of 10° as measured along the Dec axis. This means the line is drawn along the RA = 69.57° line. Notice how the fuchsia line along the Dec axis is more than twice the length of the mauve line along the RA axis, even though they both define 10° along their respective axes. Only the Dec value of 10° represents the true angle subtended by the fuchsia line, as measured from the reference frame origin at the centre of 67P. The mauve RA value of 10° does not represent the true angle as measured from the reference frame origin. It represents the number of degrees around the circle represented by Dec = +64.01°. That circle is cos 64.01 = 0.438 of the size of the circle along which Dec is being measured. Dec, however, is measuring round an RA line, 69.57°, which is a great circle or circumference line. RA lines are always great circles. Dec lines are not great circles (barring just one, the celestial equator). Dec lines are diminishing hoops like latitude lines. Thus the RA degree increments along Dec = +64.01° are 0.438 times smaller than the Dec increments along RA = 69.57°. 

To be clear, RA is always defined as the RA component of the coordinates as viewed from the origin. It’s not viewed from the centre of the small Dec line circle that the RA coordinate is sitting on even though RA ticks off degree units around that circle. The observer sits at the RA/Dec origin and observes these ticked-off degree units from below as they arc around in a small circle above him. The ticked-off degree units allow the observer to locate the RA position of an object along that circle and the circle is itself the Dec component of the coordinates. But that’s as far as it goes: the ticked-off RA degrees (in raw form) have nothing to do with the true angular distance travelled by the object as viewed from the origin. Those degree units are simply too small because they’re ticking their way around a smaller circle than the great circle that the Dec degree units are ticking round. Being too small, they tick off an angle that’s greater than the true angle of travel as measured at the origin. This means the raw RA measurement has to be multiplied by the cosine of the Dec line they’re measuring along in order to give the true angular distance of travel along the RA axis. And it should be stated that this is only applicable to short distances such as the figure 2 data plot with an RA spread of just 1.2°. Any greater RA spread for a straight-line angular distance and the track climbs the Dec lines, introducing non-linear effects.

The small Dec circle and the sphere it’s sitting on, as described above, aren’t usually thought about very much. Their relative proportions remain the same at whatever r value from the origin they are measured whether a tiny sphere at the reference frame origin or the infinitely large celestial sphere. The infinite number of congruent cases between those two extremes proves that RA degree increments are always smaller than the Dec increments to the tune of the cosine of the Dec value along which they’re measured. For the 67P spin axis, the radius of the Dec circle is cos 64.01 of the sphere radius at which Dec is measured. RA units at Dec = +64.01° are therefore smaller than the Dec units by a factor of cos 64.01 = 0.438. 

As another example, at Dec = +45°, RA degree increments would be 0.707 (cos 45) of the Dec value. Dec increments always stay the same and at parity with the angle as measured at the origin but RA varies and never represents the angle as measured at the origin except along the celestial equator where Dec = 0° and cos 0° = 1 i.e. unity.

Photo 6- an uncluttered version of photo 5 with just the end points of the RA 10°-long line and the Dec 10°-long line. The orange spin axis location for 67P is in the middle, as before. The spin axis points at this spot on the celestial sphere.

Photo 7- this is the same as photo 6 but with a large, yellow circle drawn around the orange spin axis dot. 
In photo 7, the yellow circle has a diameter of 10° of RA because it kisses both mauve dots at either end of the 10°-long RA line. However despite being a circle which, by definition, has a constant diameter, that diameter only measures 5° along the 10°-long Dec line. We know this because it reaches only halfway to the two fuchsia end points. If the dotting were more professional the Dec-axis diameter, measured in Dec degrees would be around 0.438 of the RA-axis diameter measured in RA degrees. It wouldn’t be quite exactly that proportion because the 0.438 coefficient corresponds only to the +64.01° Dec value at the orange dot. But this illustrates a principle: circles drawn on the celestial sphere at high Dec values measure ‘longer’ as measured in RA degrees along the RA axis than they do in Dec degrees as measured along the Dec axis. This is despite having constant diameters by definition. 

It follows from the above, that if the RA and Dec coordinates of the circle are transposed to an isotropic plot, that is, a Cartesian graph with RA and Dec axes with equally spaced degree units, the circle will be stretched along the RA axis into an ellipse. This is what has happened in figure 2, above, and it’s the essence of the error to be described below in this post.  

The bright green dotted line in photo 7 shows a hypothetical asteroid track across the sky close to the celestial pole. This could apply to an asteroid passing 67P but perhaps it’s easier to unclick the RA/Dec reference frame origin from 67P’s centre of gravity and clip it into place at the Earth’s geocentre. Now the bright green track is an NEO flying almost over the Earth’s North Pole and projecting a track onto the celestial sphere, tracking past the celestial pole. The celestial pole is where the Earth’s spin axis or North Pole points, like 67P’s orange dot. The bright green line subtends an angle of 10° at the geocentre. We can ascertain this because it’s the same length as the 10° distance between the Dec lines. And yet it travels through 105° of RA. This is a more exaggerated version of the yellow circle with the 0.438 coefficient. The ‘RA degree measurement’ of the NEO track is 10.5 times the real value of the angular travel as measured from the geocentre. So it’s a coefficient of 1/10.5 = 0.095.

Photos 8 and 9

Photo 8 credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)Creative Commons Attribution 3

Photo 9 credit: 

Creative Commons Attribution 3

Photo 8 is a celestial star chart similar to those above. It shows Draco in the middle, a long, sinuous constellation at around the same average Declination as the yellow circle around 67P’s spin axis in photo 7. Notice how Draco bends up and down quite markedly. 

Photo 9 is an isotropic RA/Dec plot of the whole sky (RA and Dec plotted with equal degree units). In this plot, all constellations at high Dec values have to be stretched along the RA axis. You can see Draco stretched into a long line that’s much less wavy than its real shape (it at the top and says “Dra” near its left-hand end). This proves that if you transpose raw RA and Dec values to an isotropic plot, the real-world shape you’re trying to depict will be stretched drastically along the RA axis if that shape resides at around Dec = +64.01°. This is what happened in the case of the ‘elliptical’ spin axis data pattern in figure 2 of Gutiérrez et al. (2016). That pattern should in fact be circular. The attempts at modelling the spin axis to fit the ellipse led to difficulties in constraining the moment of inertia and excitation values. Those difficulties arose from the misapprehension that the spin axis was describing an elliptical pattern as it precessed, instead of the real-world circular pattern. 


This part concerns an erroneous interpretation of 67P’s spin-axis precession data in Jorda et al. 2016. The paper’s title is, ‘The global shape, density and rotation of Comet 67P/Churyumov-Gerasimenko from preperihelion Rosetta/OSIRIS observations’, by L. Jorda et al. published in October 2016. 

This paper has been cited eight times as of the date of this blog post (November 2016), including pre-publication citations made when it was in the submission phase. 

One of the citing papers, Gutiérezz et al. (2016), relies heavily on the erroneously interpreted spin-axis data and it attempts to model the spin axis precession accordingly but this means it’s labouring under the assumption that the RA and Dec data points locating the spin axis movement are compatible with each other. They’re not compatible in their current form as plotted in that paper’s isotropic plot (figure 2) and without the RA component of each data point being adjusted for the isotropic nature of that plot. The paper’s conclusion says that when RA and Dec data are considered together they “do not allow constraining the inertia moments and excitation level” that characterise the spin axis precession. However, when RA and Dec are considered separately, there is some success in detecting “significant combinations of parameters”. It’s argued here that this is because the RA component of each data point isn’t compatible with its corresponding Dec component due to not correcting the RA component for the isotropic plot. The full title of the citing paper is ‘Possible interpretation of the precession of comet 67P/Churyumov-Gerasimenko’ by P.J. Gutiérezz et al. (2016). 

It was the Gutiérezz et al. (2016) paper that prompted me to realise there was a problem with the precession data, specifically their isotropic graphs showing the spin axis data points plotted with right ascension (RA) and declination (Dec) for the two axes. Since it’s this paper’s graphs that allowed me to prove the data misinterpretation, this part will focus on the Gutiérezz et al. paper and not the Jorda et al. paper. 

In pursuit of full transparency, I have not read the Jorda et al. paper. It’s paywalled, whereas I was able to get access to the Gutiérezz et al. paper. Since Gutiérezz et al. cites the Jorda et al. findings very clearly and then plots them, it follows that the critique below of Gutiérezz et al. must also apply to Jorda et al., the original source of the misinterpreted precession data. If this reasoning is somehow misinformed, I shall be happy to make a correction regarding Jorda et al. but the data and graphing as presented in Gutiérezz et al. would still be at fault. Since both lead authors are co-authors on the other’s paper, and the error is common to both papers, it seems appropriate to critique the error itself and apply it to both papers.

Another reason for focussing on the citing paper, Gutiérezz et al. (2016) is that their modelled ellipse in figure 5, that best fits the observed data, is used for the calculations below (see the calculations heading). Figure 5 is the second header image.


In the following analysis “the observed data” is the term used for the 232 RA/Dec coordinate data points for the 67P spin axis position in Jorda et al. (2016). This data set is called the “observationally derived data” in Gutiérrez et al. (2016), although they stripped out 7 outliers leaving 225 data points. The 232 data points were observed over 125 days in late 2014. They were taken in successive 10-hour blocks. Each point is therefore the average RA/Dec position of the 67P spin axis during each 10-hour block.

In essence, the error could be described as an artefact of the RA/Dec coordinate system finding its way into the isotropic precession graphs of Gutiérezz et al. (2016) without being corrected for. It is this artefact that has produced the ellipses in those figures. They should not be ellipses, they should be near-perfect circles.

Keeping this in mind, the last paragraph in the ‘Summary and conclusions’ of the paper is revealing:

“To evaluate whether it is possible to constrain the inertia moments and excitation level, a systematic search of the probability of compatibility between simulated and actual RA/Dec patterns by means of two-sided K-S tests was performed. Even if it is possible to find very significant combinations of parameters [Iy, Iz, EI] when RA and Dec coordinates are considered separately, K-S probabilities when RA and Dec data are considered together do not allow constraining the inertia moments and excitation level.”

It’s proposed here that the reason significant combinations of parameters can be found for RA and Dec coordinates, when considered separately, is that, at Dec = +64.01°, the RA and Dec values in the observed data are each measuring different real-world angular distance increments of the nutation angle, theta. Specifically, the RA values in the observed data cover more RA degree units for the same angle as the Dec degree units do. We are referring here to when measuring an angle at the origin of the RA/Dec reference frame (such as theta) first along the RA axis and then measuring the same angle along the Dec axis. The same angle spans 2.282 times as many RA degree units as Dec units. The same applies to a theta angle that is not aligned along either axis and thus is composed of an RA and a Dec component. These two-component data points for theta constitute almost all, if not all, of the 225 data points in figure 2. The RA component stretches the circular precession pattern into an ellipse via the 2.282 coefficient. This is why the ellipse’s major axis is aligned with the RA axis. 

The angle, theta, is the angle of the spin axis nutation as measured from the origin of the RA/Dec reference frame. The origin is at the centre of gravity of the comet. The angle of nutation is the angle between the angular momentum vector and the spin axis. The angular momentum vector is the putative average of the 225 observed data points in figure 2. So it’s sitting in the middle and can be seen more clearly in figure 5 as the centre of the modelled/fitted ellipse. It’s also the centre of the circle when the ellipse is corrected. 

The angular momentum vector is at one and the same with the inertial axis, Z, about which the intrinsic spin axis, z, precesses. We can keep the terms Z and z in the back of our minds after the short explanation below. After the explanation, they’ll be referred to by their familiar names: the angular momentum vector (which is Z) and the comet’s spin axis (which is z). 

Z and z are used for transforming (or relating) the precessing cometcentric reference frame to an unmoving inertial frame. Z is one axis of the XYZ fixed reference frame that is outside the xyz intrinsic comet frame of which z is one axis. Z and z are axes which means they are both one-dimensional lines. 

Both reference frames have a common origin at the centre of gravity of 67P and thus z joins Z at the origin. All we have to remember here is that Z is the angular momentum vector and it’s a line fixed in space. And the spin axis, z, is a line that moves around Z, while joined to it at the origin. z moves around Z only if it happens to be precessing, which it is for 67P. 

Since z is locked to Z at the origin it moves round Z, sweeping a cone, with its base locked in one place. Z is then the average central axis within the long, thin cone that’s swept out. If the spin axis isn’t precessing, it merges with the angular momentum vector (z merges with Z). They then become one line pointing from the centre of gravity of the comet, along the spin axis/angular momentum vector to a point on the celestial sphere at RA, Dec = 69.57°, +64.01°. 

This RA/Dec value is the Jorda et al (2016) value, as defined by their 232 spin axis data points. Gutiérrez et al. (2016) removed 7 outliers to arrive at the 225 points, as stated above. This shifts the RA/Dec value for Gutiérezz et al. (2016) by a very small amount. However, since the original Jorda et al. (2016) data interpretation was the input for Gutiérrez et al. (2016) it would be best to stay with the Jorda et al. (2016) angular momentum vector coordinates even though the graphs in the header show it to be a fraction off due to stripping the 7 outliers. You have to look hard to see the difference anyway because it’s a judged average centre-point of all the dots, and it makes no difference at all to this analysis. 

The offset angle, theta, is the nutation of the spin axis from the angular momentum vector. Theta is the traditional term for nutation in any discussions about precession. Theta is shown in figure 4 in Gutiérrez et al. (2016). It’s not shown here but nutation is described below. 

Much focus is placed here on the actual origin of the RA/Dec reference frame, which is placed at the centre of gravity of 67P, and the fact that theta, the nutation, is measured at the origin. This is fundamental to understanding the nature of the figure 2 and figure 5 RA/Dec anomaly.

As the spin axis precesses around the angular momentum vector with any given theta value for the nutation, it describes a circle. That circle may become a smaller circle as the theta angle is reduced or a spiral as theta is in the process of growing or diminishing. The result of taking 225 10-hour averages of the spin axis coordinates along these circles and spirals of varying radius, results in a pattern or shape that is a notional circle filled with 225 dots. This has been stretched into a notional ellipse by the RA anomaly. Notional, because they aren’t those exact shapes but appear strongly to suggest them.

The angular momentum vector can be thought of as a laser beam pointing from the RA/Dec origin at 67P’s centre of gravity and out to the celestial sphere at RA, Dec = 69.57°, +64.01°. It stays rigidly pointing at that spot, a single laser point. Meanwhile, the spin axis of the comet can be thought of as another laser beam, pointing from the origin as well, and describing the circles and spirals of different radii on the celestial sphere. These circle around the fixed laser point of the angular momentum vector and as the radius of the circles change, they betray the change in the nutation angle, theta. 

The spin axis therefore sweeps a cone as mentioned above. These cones are of varying sizes according to the radius of sweep (the described circles) or become deformed cones when the radius is spiralling. The radius of the described circles is very small, just a few tenths of a degree. Theta is therefore the angle between the two lasers and it’s measured right down at the origin of the RA/Dec reference frame, which is the common end point of both lasers.

Theta is determined by the combination of the RA and Dec readings, specifically, their vector product. These are also measured from the origin of the RA/Dec reference frame, which is placed at the centre of gravity. So far, so good, but we should take pause to note that it is this common origin for measuring theta and also RA/Dec is the source of the confusion causing the RA anomaly.  

We should be able to ‘sit at the origin’ look up, along the line of the angular momentum vector, and see the angular displacement (nutation/theta) of the spin axis away from the fixed angular momentum vector. That angle may or may not vary over time as the spin axis precesses round the angular momentum vector over time. In the case of 67P, theta does vary, causing the spread of the data points and that’s why they fill the ellipse in figure 2 (which should be a filled circle).

At any instant in time, the angle theta can be taken by reading forwards/backwards along the RA axis a certain number of RA degree units from the fixed angular momentum vector; and then reading up/down along the Dec axis a certain number of Dec degree units. However, the RA and Dec values in the observed data are each using different real-world angular increments distances along the RA and Dec lines as they ascertain the angle theta. More specifically, the RA degree units do not measure the same angular distances as those angular distances used for ascertaining theta. This is despite the fact both RA and theta are using the same RA/Dec origin. This is crucial and it is the source of the anomalistic interpretation of the data, which in turn, leads to the ellipses in the figure 2 and figure 5 graphs, which should be circles. 

This phenomenon of different angular measurement scales for RA and Dec is simply an idiosyncrasy of the RA/Dec system, one which is especially apparent at high Dec values where the incremental RA degree units along the Dec lines do not represent the actual angle in degrees as measured for theta at the origin. This is because the RA degree units are doing there own thing: they’re measuring their way around a smaller circle, akin to a latitude line. The radius of this circle is smaller than the radius of the sphere it’s a part of. It’s smaller by a factor of the cosine of the Dec angle of the ‘latitude’ circle that’s being measuring around. 

Meanwhile, each Dec degree angle increment really is measuring the true Dec axis angular component of the theta angle, as measured from the origin. This is because the Dec lines are like latitude lines and, by definition, they’re measuring the true angle between the equatorial plane and that Dec value. So the Dec data in figure 2 presents no problems at all. But each and every Dec value in the figure has been slid backwards or forwards along the RA axis by its rogue RA counterpart while remaining at the correct Dec value. This results in the area that the 225 data points define being stretched to the left and right, either side of the central RA value of 69.57°. As the data points are sliding right and left too far along the RA axis, they’re maintaining their correct Dec position and so the area represented by the 225 data points doesn’t get stretched from top to bottom, only from left to right. 

The +64.01 Dec value for the angular momentum vector at the centre of the observed data is a fairly high Dec value (two-thirds of the way towards +90°) so the anomaly is very significant. The value of the anomaly is a coefficient of cos 64.01, which is 0.438. This leads to a correction factor of 1/0.438 that’s needed when transposing the RA data to the isotropic plot in figure 2. The reciprocal of the cosine, 1/0.438 is 2.282 so the data we see in figure 2 is stretched along the RA axis by a factor of 2.282. It needs to be de-stretched by the correction factor of 0.438. When that’s carried out, the ellipse de-stretches to become a perfect circle. This circle will be the true circular pattern that defines the precession of the spin axis around the angular momentum vector. 


In contrast to the RA degree units, the incremental Dec degree units always represent the actual angle as measured at the origin. As stated, it is just an idiosyncrasy of the RA/Dec system and is an exact analogy to the longitude degree lines on the Earth at 64° latitude being bunched together much more than the latitude lines. The correction factor in this analogy is again 2.282. 

One degree of latitude always covers 111.2 km whether at 64°N, 15°N or 85°S. However, one degree of longitude always varies according to the latitude line along which it’s being measured. At 64.01°N, it happens to cover 48.729 km. The latitude value of 111.2 km for one degree really does subtend an angle of one degree at the centre of the (Lat/Long) reference frame at the centre of the Earth. However, the longitude value of 48.729 km for one degree does not subtend an angle of one degree at the origin. It subtends an angle of 0.438° at the origin and 0.438 is cos 64.01. 

Thus, any real-world distance in km, measured in degrees of latitude or longitude across the earth presents us with a problem: at 64.01° latitude the same distance in km will be 2.282 times ‘longer’ in longitude degrees than it is in latitude degrees. A distance of 1.112 km measured South to North (up the latitude ‘axis’) will measure as being 0.01° but the same distance measured West to East (along the longitude ‘axis’) will measure as being 0.0282°. And yet both measurements are measuring the same distance across the surface and along each axis. And that distance subtends an angle of 0.01° at the centre of the Earth. So a 0.0282° longitude measurement of a 1.112 km distance along the surface corresponds to a 0.01° angle when that distance subtends an angle at the geocentre. Measuring the 1.112 km distance from the geocentre is the same manner which theta would be measured in the RA/Dec reference frame i.e. from the origin of the reference frame. The reason for this 0.438 factor at 64.01° latitude is that the centre of the 64.01° latitude circle isn’t at the centre of the Earth. It’s at the centre of the plane defined by the 64.01° latitude line. The radius of that circle is the cosine of 64.01 timesed by the radius of the Earth i.e. 0.438 of the radius of the Earth. Consequently the circumference is 0.438 of the circumference of the Earth. Therefore, each longitude degree increment around that circumference measures a distance that is 0.438 of the distance measured by each latitude degree increment around the circumference of the Earth. And the only way to measure the angle at the centre of the Earth as subtended by a distance at the surface is to measure it in degrees along a great circle i.e. along the circumference of the Earth as latitude angles always do. Longitude angles do this only along the equator. Above and below the equator, they start bunching together. They’re not then measuring the angle subtended at the centre of the Earth but at the centre of the latitudinal, cross-sectional plane at which the measurement is being made. 

There’s one crucial difference between this lat/long analogy and the RA/Dec system. Despite the RA (‘longitude-type’) increments being concertinaed together and not measuring the true angle as measured from the RA/Dec origin, they are still used as an angular measurement from that origin. This leads to apparently large angle swings when measuring at high Dec values, near to the poles, even when the real angle swing is actually very small. NEO’s that pass over the poles show near-180° swings in RA in the space of a few minutes when in fact they’ve only moved comparatively slowly and by an angle of 10° or 15°. They move through all the bunched-up RA lines near the poles at apparent break-neck speed. But it’s the very small distances between the RA degree lines that are causing this phenomenon (see the bright green line in photo 7).

This phenomenon was nicely illustrated with the well-documented close approach of 2012 DA14 in February 2013 when it swung to Dec = -87°, right under the South Pole. I’m very familiar with this phenomenon from reading the ephemerides of hundreds of close-approaching NEO’s: a small angular distance travelled (akin to theta) as measured from the RA/Dec origin can cover five or ten times that angular distance in RA if it’s at a high Dec value. The real angle is the small one travelled, akin to theta, and the RA angle component is just a rather clumsy and confusing way of representing it. The Dec component isn’t a problem: it records the true angle travelled up/down the Dec axis as measured at the origin. 

The RA value bears no relation to the actual theta angle as measured from the origin unless it gets crunched through the cosine of the Dec angle at which the RA is being measured. And to be precise, it’s the inverse of the cosine that operates on the RA value to give the true theta angle at the origin. The single case where the RA value is the same as theta is when the RA is being measured around the celestial equator. In the case of the NEO approaches, the 10°-15° of angular travel, if in line with the equator, would show up as 10°-15° in RA, i.e. at parity with the real angle as measured from the geocentre. That would be as opposed to 180° of RA when measured as it goes 10°-15° over the pole from one side to the other (or, say, 150° of RA if a little offset from the pole).


For the 67P case, we can keep the lat/long analogy in mind while substituting RA for longitude and Dec for latitude. We can set the angular momentum vector so it’s fixed to the origin at one end (as it always is) and pointing rigidly at RA, Dec = 69.57°, +64.01°. Then we can measure the deviation of the spin axis from the rigid angular momentum line (which is the nutation of the spin axis, theta) and measure it in RA degrees and Dec degrees as Jorda et al. (2016) did and Gutiérrez et al. (2016) reproduced. 

In this case, any Dec degree value measured up and down the Dec axis from the angular momentum vector really does correspond to one degree as measured from the origin of the RA/Dec reference frame. 

Conversely, any RA degree value measured backwards and forwards along the RA axis from the angular momentum vector does not correspond to one degree as measured from the origin of the RA/Dec reference frame. It corresponds to just 0.438° when measured along the 64.01° Dec line. And 0.438 is cos 64.01.

Thus, all RA degree unit measurement values for the nutation angle, theta, as measured from the origin are 2.282 times greater than the Dec degree unit measurements for the same angular displacement (at Dec = +64.01 or very close to it, as the 225 data points are). The 2.282 coefficient is 1/cos 64.01. 

Dec is always in parity with the real theta angle component as measured along the Dec axis but RA is always 2.282 times greater than the real theta angle component as measured along the RA axis. This means all the RA components in each and every RA/Dec data point (the observed data in figures 2 and 5) have to be divided by 2.282 when transferred to an isotropic plot (i.e. multiplied by 0.438 = cos 64.01). The resultant shape of the corrected data spread will be a filled circle.

With the adjustment made, there will be no additional bias of the nutation angle, theta, along the RA axis in both directions either side of the angular momentum vector. The angular momentum vector is positioned at the centre of the data points in figure 2. 


Since we’ve looked at the RA/Dec increments in such detail, you may have noticed the RA scale increases to the right in figure 2 but to the left in the conventional manner for the star charts in photos 3 to 9. This is because in figure 2, we’re looking down the angular momentum vector towards the 67P RA/Dec origin at its centre of gravity. So we’re looking down from the celestial sphere and figure 2 has its RA scale back-to-front as if we’re behind a screen that’s got the celestial sphere projected onto it from 67P on the other side. The angular momentum vector, at the centre of all the dots, is pointing directly out of the screen at us- we’re looking straight down it towards the RA/Dec origin and that’s sitting behind the screen and behind the data points. The plane of the data points (the screen) is at right angles to the line of the angular momentum vector and all the data points are piercing holes in the screen where the spin axis was when measured. If we use the laser analogy and shine 225 lasers from the origin, through the holes to represent the 225 spin axis positions, those lasers would all shoot past us to our right, left, etc., just missing us and would describe the circular precession pattern on the celestial sphere ‘just behind’ us. We’re sitting right in the middle of that circular pattern of circles and spirals drawn on the celestial sphere. 


The RA-axis stretch is a strong clue that it’s an artefact of the transposition of raw, uncorrected data from RA/Dec to an isotropic plot. It also explains why, according to the quote above from Gutiérrez et al. (2016), the inertia and excitation parameters couldn’t be constrained when RA and Dec were analysed together. They could only be constrained when the RA and Dec components for each of the 225 data points were separated out and analysed as two different data sets. 

When they remain unseparated, the RA/Dec taken as a single data set, are smudging the circle into an ellipse and this shape can’t be modelled because it’s an ersatz precession pattern. When the RA and Dec components for each and every one of the 225 data points are treated separately as two sets of 225 data points, the data is internally consistent and patterns reflecting the true, hidden, circular-shaped pattern are betrayed. When the RA and Dec components are merged for each data point, as we would normally assume we can do in order to model useful precession patterns, they represent a vector product. The vector product is the diagonal product of the distance along the RA scale (the RA component) and the distance along the Dec scale (Dec component). But because of the 2.282 stretch in RA, the vector product is smudged and the data points become ever-more difficult to reconcile as one progresses from the central RA value to the left extremity and right extremity of the ellipse. Put another way, the vector-summed data is not internally consistent, and is therefore representing an ersatz precession pattern. This means it can’t be modelled with reasonable inertia moment and excitation levels. This explains the failure in Gutiérrez et al. (2016) to constrain the inertia moments and excitation values for RA and Dec when analysed together as a single data set.


Regarding Gutiérezz et al. (2016), on page 2 of the paper, it says:

“By applying the SPC method [stereo-photoclinometry*], Jorda et al. (2016) retrieved a spin axis that moves around (RA, Dec) = (69.57°, +64.01°). Jorda et al. (2016) obtained that the spin axis does not describe a circumference, but approximately fills an ellipse in an isotropic plot (Fig 2).” 

This quote is a citation of the precession data interpretation in Jorda et al. (2016). The figure 2 graph they’re referring to is stated as being that data from Jorda et al. (2016) and indeed the caption of figure 2 cites the data, if not the graph itself as coming from Jorda et al. (2016). This is the reason for including Jorda et al. (2016) in this analysis.

*stereo-photoclinometry is a method by which a shape model of 67P was constructed using stereo landmarks of the comet’s position and attitude in OSIRIS photos.
Gutiérezz et al. (2016) go on to say that this “ellipse in an isotropic plot” is at odds with the circular precession plot determined in Preusker et al. (2015). So Gutiérrez et al. (2015) certainly regard the Jorda et al. (2016) ellipse in figure 2 as being the physical shape of the precession and not just a shape on the graph that somehow represents a different shape for the actual precession. The difference between the Preusker et al. (2015) circle and the Jorda et al. (2016) ellipse seems important enough to be noted. And yet, as we’ve seen above, the ellipse is indeed just a shape on the graph that represents a different shape for the actual precession which is a circle. 

The key term here is “isotropic plot”. This is the source of the ellipse anomaly. The plotted data describe a filled ellipse but they should describe a filled circle. 

The conclusion of the paper has already been quoted above as saying that the RA/Dec data couldn’t allow the inertia moments and excitation to be constrained when RA and Dec were analysed together. It only showed “significant combinations of parameters” (inertia moments and excitation levels) when RA and Dec were separated. This was also apparently the case for the Lomb periodograms (various figures in the paper). These are presented with separated RA and Dec in all cases. The peaks show remarkable correlation between the RA and Dec values- their respective peaks nest into each other very well. However periodograms of the mixed RA and Dec data are not considered. Gutiérezz et al. (2016) also say of Jorda et al. (2016):

“Interestingly, Jorda et al. (2016) analyzed the spin axis orientation by means of the phase-dispersion minimization technique [to obtain a periodicity of 276 hours] from separately considering the RA and Dec coordinates.”

Thus, RA and Dec were separated wherever possible, for Lomb periodograms, K-S probabilities and phase-dispersion minimization. The only instance where RA and Dec were mixed was in the unavoidable situation where the physical shape of the precession data had to be modelled. For the shape to exist at all, it required the vector product of both RA and Dec for each data point in order to spread out into the ellipse shape in figure 2. When this was modelled using the Euler equations cited in the paper, difficulties arose resulting in the inability to constrain the parameters due to closing the central hole while using reasonable parameter values. As the conclusion states:

” K-S probabilities when RA and Dec data are considered together do not allow constraining the inertia moments and excitation level.”

Since the K-S probabilities are “a function of Iy and El” (figure 9 caption) and Iy and El are the y inertia moment and excitation level, it follows that the above quote is referring indirectly to the modelling of the inertia moments and excitation level via the Euler equations and with RA and Dec considered together. 

Furthermore, figure 9 shows this indirectly stated anomaly in the form of two white lines, one continuous and one dotted, in both of its two frames. These lines represent the “excitation level for each Iy associated with the highest K-S probability” when RA distributions are compared (continuous white) and Dec distributions are compared (dotted white). Please see figure 9 and its caption below). I would suggest that when the 0.438 coefficient is applied to the RA data in figure 2 and the Euler equations applied once again to model what is now a circle, the two white lines in figure 9 will automatically merge. This would still involve separated RA and Dec components but it would indicate that RA and Dec can indeed be mixed in a similar K-S probability graph. And when this is done the K-S probabilities, when considering RA and Dec together, should after all allow constraining of the inertia moments and excitation level.

Photo 10- Figure 9 from Gutiérrez et al. (2016) 

Credit: Gutiérrez et al. (2016)Astronomy and Astrophysics590, A46 (2016)DOI: 10.1051/0004-6361/201528029Copyright ESO 2016


It’s interesting to note that the ellipse described by the observed data is orientated exactly along the RA axis when characterised by the modelled ellipse in figure 5. This is a very strong indicator that if there were any anomaly, it’s entirely to do with the RA axis. This is a smoking gun for the phenomenon described above: the artefact resides entirely in the squashing-together of the RA degree units; the Dec degree units remain the same size in the Equatorial reference frame, from -90° to +90° and can therefore be transposed to the Cartesian graph without distortion. This means that the y-axis (Dec axis) spread of the data points in figure 2 really do represent the angular diameter of the precession circle as measured from the RA/Dec origin at 67P’s centre of gravity. All the stretch is along the x-axis (RA axis). 

The second thing of note is that it is an ellipse and not, say, a notional square with rounded sides or an amorphous shape. An ellipse is by definition a circle that’s been stretched along one axis only. Again, this reinforces the idea that there’s an artefact operating along just one axis. This, coupled with the fact that this one axis is aligned with the RA axis, is very strong evidence for the RA anomaly.

The third piece of evidence that shows it’s a circle stretched into an ellipse is that the major axis of the ellipse is very close indeed to 2.282 times longer than the minor axis. Since this is 1/cos 64.01 and the observed data are centred on Dec = 64.01°, it means that when the RA degree units are reduced to 0.438 of there current figure 2 size, a circle will be obtained.*

*Please note, only figure 2 is fully isotropic and amenable to the 0.438 coefficient operation. Figure 5 and thereafter have an RA axis that is actually slightly squashed- by a factor of just 0.916 though, not 0.438. To adjust these graphs correctly the 0.916 factor has to be taken into account. The 0.916 factor is akin to applying only some of the 0.438 coefficient: squashing together the RA degree units a bit but nowhere near enough. 


On-screen measurements of the ellipse major and minor axes in figure 5 were subject to perhaps a 2% error. For figure 2, estimating an ellipse that’s not drawn in, it was probably a 5% error. Actual measurement values aren’t shown, just the ratios they imply. This is because they were taken at arbitrary levels of zoom. The proportions remain valid for any given zoom value. 

Calculations are taken to three decimal places for precision but that precision is greater than the error bars. Despite this, the measurements of the ellipse in figure 5 (along with the necessary 0.916 adjustment) produced an inferred Dec figure of 64.01°. This was pure chance and is purely down to a) luck in the measurement within the 2% error bars and b) various roundings up and down to 3 decimal places. It’s definitely not indicative of a systematic error in the methodology as one might be tempted to think.

The target value to look for in the ratio of minor axis divided by major axis of the ellipses is cos 64.01° which is 0.438. 

A measurement of the raw data in figure 2, on the assumption it fits to an estimated ellipse produced the following figures:

Minor axis divided by major axis = 0.469

Cos-1 0.469 = 62.03°.

So from the ellipse in figure 2, we can infer a Dec value of ~+62° which is close to the +64.01° value, which is the central RA, Dec figure around which the observed data is spread. 

A measurement for the modelled ellipse in figure 5 produced the following figures (including the 0.916 adjustment for the slightly squashed RA axis):

Minor axis divided by major axis = 0.478. 

But the RA axis needs to be stretched by 1/0.916 so as to obtain a truly isotropic relationship before applying the cos-1 rule. This is done here a slightly different way. It’s done by reducing the minor axis to 0.916 of its measured value, which is the same as multiplying the 0.478 minor/major ratio by 0.916. 

0.478 x 0.916 = 0.438 (this is the exact target value). 

Cos-1 0.438 = 64.01° (this is exactly the same as the observed central Dec value)

Thus, the inferred Dec value for the figure 5 modelled ellipse is 64.01°, which is exactly the same as the the actual central figure in the modelled data. With the RA anomaly corrected for, and the fact that the resultant inferred Dec value is the same as the observed Dec value, it means the spin axis was indeed precessing in a circular pattern around RA, Dec = 69.57°, +64.01° and not in an ellipse. 


Once the observed data was plotted onto an isotropic axis, it meant that the circular precession was depicted as an ellipse. This ellipse was then taken as the basis for modelling the precession. 

The modelling software would have modelled an elliptical precession in order to fit it to the apparent elliptical precession in the observed data. This would have affected the values chosen for the excitation level and inertia moments. If modelling a circular precession, however, these values would presumably need to be changed. This in turn would have implications for ascertaining the homogeneity of 67P. 

Figure 5 had a hole in the middle of the modelled ellipse that fitted the elliptical version of the observed data. On page 5, it’s stated that this hole could be reduced only by reducing the nutation and therefore the excitation level. This would in turn mean introducing some inhomogeneity for 67P. However, the hole in the modelled version is based on trying to fit an ellipse to what is actually a circular pattern to the precession. 

By rerunning the modelling and basing it on the true circular pattern, it may show that the hole can indeed be filled in and with no invoking of inhomogeneity. 

The true circular pattern of the observed data may imply a subtly varying nutation describing a spiral. That seems an intuitively possible dance for a comet’s spin axis to perform, but I suspect it would be difficult for 67P to perform that trick in ever decreasing/increasing ellipses. This is because it implies a simple harmonic motion (SHM) component to the nutation value on each and every rotation about Z, the angular momentum vector. 

The fact that the one axis along which nutation variations are happening corresponds to the RA axis is a sign that something is amiss. This is further illustrated in the related issue of finding a better fit by separating out all the RA and Dec values and plotting them separately. There is nothing inherent in the geometry of space that should show up patterns (better/worse fits) that align with a man-made coordinate system based on the random value of the Earth’s tilt and the randomly chosen First Point of Aries (RA = 0°). This better fit of the separated RA and Dec values betrays something ersatz about the data. It’s showing the RA stretch anomaly when the RA data is mixed in with the Dec data. It’s distorting the overall data via the stretched vector product.

If the true circular pattern of the precession is used to model against, only the gradual linear reduction and increase in nutation over time is needed to fill the central hole. That way, no SHM in the nutation value needs to be invoked to describe an ellipse while trying to close the hole at the same time. Thus the hole would be closed and opened over a longer circular/spiralling cycle.


In summary, the precession that was measured in Jorda et al around the central RA, Dec value (69.57°, +64.01°) had to describe some sort of shape whether an ellipse or a circle. However, if it was indeed a circle, it would be stretched into an ellipse if it were transposed in raw form from the Equatorial RA, Dec system into a Cartesian system using equal axis increments (an isotropic plot). The only way the shape of the precession can be faithfully reproduced on the Cartesian graph is if the Cartesian axis units are proportioned in such a way as to reflect the RA, Dec proportions at Dec = 64.01°. This means bunching up the RA units so that they are only 0.438 (1/cos 64.01) of the Dec units. When this correction is done in the case of figure 2, a perfect circle is obtained.

The ellipses in figure 2 and figure 5 in Gutiérrez et al. (2016) are therefore depicting an anomalous artefact of the RA, Dec system. The same applies to the other ellipses in the subsequent figures of the observed data.

Part 67- Ma’at 02 Shows no Changes (Contrary to OSIRIS Findings)


UPDATE 12th April 2017

The lead author of the paper in question, Jean-Baptiste Vincent, responded to my email notifying him of this blog post. I’ve pasted it below. I’d refrained from doing so before now because it mentioned new discoveries that were as-yet unpublished but as of the date of this update two recent papers appear to have covered them. The original blog post begins after “///END”.

Dear Andrew,

I finally found some time to read your blog post and think about your criticism of the claims we made in the paper I published last year. As mentioned before, I strongly recommend that you publish your work in a scientific journal. MNRAS (Monthly Notices of the Royal Astronomical Society) is planning a new Rosetta special issue, with a submission deadline of 31 March 2017. I think you should submit a paper there.
Now regarding blog post #67. I would like to first clear some misunderstanding. 

The images you mention (Ma’at pit #2), are published in far lower resolution than the raw data we used for the analysis, and the conversion to jpg often introduces artifacts. Therefore, you should consider all these images as qualitative data only, and refer to the raw data for quantitative measurements. The raw images are publicly available on the ESA server (, with a resolution of 50 cm/px. This is the typical resolution at which we studied the comet morphology.

The ellipses overlayed on the images are not intended to mark precisely the edge of the “flow”, but rather show the region of interest where we have identified changes. It is done in this way as to not force our interpretation on the reader. It’s up to you to look at the region of interest and see for yourself whether you are convinced that the flow pattern has changed, or not.

The “after” image has been rotated in the paper, as to appear with roughly the same viewing angle as the “before” image, even though it was acquired from a very different direction due to orbital constraints (we needed to keep Rosetta in the terminator plane). After rotation,the azimuth of both images is comparable, but the elevation is still different, and this introduces a perspective distortion, which must be considered when comparing the images.

Because of the change of seasons, and different local time, the solar illumination is completely different in both images, by almost 180 degrees ! This is unfortunate, but there is nothing we could do to prevent it.

Therefore, as you noted in your post, both changes in perspective and illumination may fool us into seeing changes when there are none. I must admit that there was a heated debate in our team regarding this specific pair of images. Still today not everyone is convinced that the flow has changed, although the majority of our team members supports this interpretation, which is why we published it in this way. 

And there is an other complication: we have observed in nearby areas that a significant amount of dust has moved around (a couple of meters of dust thickness removed over 100m surface, and deposited elsewhere). This large scale resurfacing is changing the local albedo of the surface and complicates even more the interpretation.

I stand by my arguments that granular flows occur on the comet, and can repeat on a short time scale. We have multiple evidence for this and have recently submitted new papers with showing avalanches on >100m scale. The areas we mention in these papers were poorly observed by the NavCam, and the OSIRIS data is not yet public, which is why you may not have seen it already.

But how to really be certain about the changes I mention in the paper? I think the best way to get rid of most uncertainties is to work in full 3D by projecting both images on the shape model and then measure precisely the edges of the features of interest. Simply comparing features from one image to the next is not sufficient because of all the problems discussed above.

Such comparison was was not possible at the time of writing this paper. Today, we have performed a 3D “before and after” in a few specific areas of the comet, and hope to apply it to Ma’at in the coming months. 

It is also interesting to note that the crash site of Rosetta was selected especially because it would give us the chance to acquire higher resolution images of the pit and flows, with illumination conditions and viewing angle closer to what we had in September 2014. This new data set should also help us understand better if we are right with our original interpretation.
I’ll be happy to send you an update when we have progressed on this topic.

With best regards,


[End of email]

Here is the hi res version of the post-perihelion photo (Zoom plus original).



The pair of photos in the header is showing the pit known as Ma’at 02, located on the head lobe at Ma’at and near the head rim. It’s also called Deir El-Medina. It will be referred to here as Ma’at 02 or just 02 where it’s clear. That’s in keeping with Parts 62-65 where it’s called 02 so as to keep focussed on its middling position between the pits Ma’at 01 and Ma’at 03. This will become increasingly important as we see the significance of the fact that 01, 02 and 03 each sit on their own delaminated layers. That will be dealt with in another part soon. 

The header pair is from the paper, J.B. Vincent et al. 2015 entitled, “Are fractured cliffs the source of cometary dust jets? Insights from OSIRIS/Rosetta at 67P”. They constitute one set of before/after observations in figure 8 of that paper, which is in section 4.3.2 “Granular flows” on page 6. There are four photos in figure 8 showing two pairs of before/after observations. The full figure is reproduced below. 

Photo 2- J.B. Vincent et al 2015 figure 8 (hereinafter referred to as figure 8). 


The lower pair of photos will be dealt with in a future post. These two before/after pairs are the only two examples cited in Vincent et al. 2015 that claim visible evidence for changes in the supposed granular flow structures. We shall be focussing in detail on the upper pair, Ma’at 02, in this post. As you can see, the before photo is dated September 2014 and the after photo is dated March 2015. The caption claims that there are visible changes between the two photos. It says:

“Top panel: flows from Ma’at regions between two of the active pits have changed; their outline is different and they seem to have expanded laterally.”

This post will show that their outline isn’t different and that they haven’t expanded laterally. Therefore, the so-called flows in the the before/after pair haven’t changed, or at least, haven’t changed in any discernible way.

The claim of changes between the two photos was already called into question by Marco Parigi on his blog:

In his post, Marco reproduces the figure 8 photo and says, “Little effort is made to connect the dots for the reader to try to work out for themselves exactly what is happening and why.”

This post, Part 67, uses 34 photos, meticulously annotated in close-up, in order to define the same detailed features in the two figure 8 photos and does so at the 5- to 15-metre scale. This analysis is at a scale that’s an order of magnitude more detailed than the 130-metre ellipse placed over the entire flow in figure 8, without any further guidance. 

Since there was no discernible change at Ma’at 02 between the two photos, it follows that evidence for ongoing changes, less still erosion, at Ma’at 02 is not forthcoming. The reason this is important is that if the pits are virtually dormant it says something about their morphological evolution: that they perhaps had a more active period in the past but that their current very low activity is insufficient to produce any discernible changes over one perihelion passage. 

Alternatively, it’s possible that their current low level of activity is indicative of past activity and the pits were therefore formed over many thousands of years. This second scenario might be at odds with the assumed 13,000-year inner solar system dynamical history for 67P. Lack of erosion evidence also has implications for the heterogeneity of 67P: if a few pits are capable of being self-excavated slowly over a long period rather than by some other means, there must be pockets of volatiles stashed under the surface. 

Of course, this blog has its own explanation for all the pits, which is laid out comprehensively in Parts 62 to 64 as well as informing Parts 32, 41, 52 and an upcoming part. It’s beyond the scope of this post to bring that hypothesis to bear on the lack of ongoing erosion at Ma’at 02, or at least, to do so in any substantive way. However, the upcoming part will deal with this and there’s also a very brief overview in the ‘stretch explanation for the flows’ sub-heading further down. 

Links to Parts 52 and 62 to 64 are at the bottom of this post. 


Firstly, the aim of this post is certainly not an attempt to disprove the J.B. Vincent et al. theory that granular material may once have flowed down gravitational slopes, here or anywhere else on 67P, at some time in the past. Nor is it tasked with disproving that cliffs may have collapsed due to sublimation-induced erosion in the past (they almost certainly have to some small extent). This cliff-collapsing is cited in Vincent et al. 2015 as a precursor to granular material no longer being supported near the cliff edge. It’s claimed that the granular material therefore flows towards and over the edge as a result of the support being removed. 

Furthermore it’s acknowledged here that cliff collapse and granular flow may be ongoing processes but happening at a very slow rate. Indeed, I may have found one such collapse at Aswan but I’m waiting for better photos. If it’s borne out, it will be the sixth separate discovery of changes over the 2-year mission discovered by Marco and me (three each). All these changes show shifted material; none proves erosion in the sense of mass-wasting. This is entirely consistent with stretch theory. 

What this post does aim to do is lay out an analysis that shows there are no discernible changes between the before and after photos of Ma’at 02 in figure 8. There may have been changes which are not discernible but the apparent changes cited in the caption to figure 8 are due to the confounding effects of 1) a different viewing angle and 2) different lighting throwing different structures into more or less relief. 


The flows are referred to as “so-called flows” above, despite the theoretical possibility that these features might have experienced granular flow. The modifiers are added because this post (and the subsequent one on the second photo pair) will show that figure 8 does not offer evidence that they have flowed either during perihelion 2015 or at any time in the past. Therefore, nothing of any substance can be said about these features actually being flows. Only speculative deduction based on their flow-like form can be made. Since they may be flows and look like flows, it would be reasonable to include the modifiers but it’s not reasonable to state as fact that they definitely are granular flows. However, now that this distinction has been made very clear here, they will be sometimes be referred to as flows for brevity from now. That’s because that’s what they are commonly known as and it’s unwieldy to keep saying “so-called flow”. 

It seems ‘flows’ and ‘flow’ are used interchangeably for Ma’at 02 and that’s continued here. It conveys the idea that there are several separate flow-like features within the entire area that’s itself deemed to be a flow. 


It would be appropriate to give this explanation at this point because it would seem strange to be exhibiting manifest scepticism for the theory that these might be ongoing granular flows without explaining why they’re thought not to be. It’s true that they’re tentatively entertained here as possibly being flows that might even have flowed recently. But stretch theory points to them being a one-off drawing out of surface material during stretch. That does admit the possibility of some small amounts of more recent, vestigial flow due to light, ongoing erosion, which would be solar-radiation induced. 

The photographic evidence for stretch being the cause of the flows and any ongoing flow being negligible to non-existent will be presented in the post mentioned as being published soon.


Header reproduced

The three confounding issues regarding the comparison of the Ma’at 02 pair in figure 8 are explained briefly below before being laid out in detail under separate headings further down. 

1- the viewing angle of the before photo is about 100° displaced from the viewing angle of the after photo. This has the effect of enhancing the apparent area of certain gentle slopes in the crumpled terrain of the flow when viewed from one direction and diminishing them when viewing from the other direction. 

2- the shadowing is noticeably different between the two photos with a lighting azimuth change of around 130° relative to the local comet surface. This has the effect of enlarging or diminishing the apparent size of (presumably) otherwise unchanged features. It also results in a substantial area of the actual pit being illuminated so brilliantly that it appears not to be in the pit but on the rim. This affects 3, below. 

3- the ellipses placed over the flow that’s claimed to exhibit changes aren’t placed over the same area. The illusion in 2 has led to a misidentification of the pit rim in the after photo. This means the ellipse in the after photo has been shunted further over into the pit so as to incorporate this fake rim in the same manner as the true rim was incorporated into the ellipse in the ‘before’ photo. This has in turn led to a misidentification of the fiduciary features around the outer perimeter of the flow because the opposite side of the ellipse has been shunted over by a commensurate amount. The result is that the entire ellipse in the after photo is shunted a few tens of metres over in a direction that is towards the centre of the pit. 

Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

Photo 3- (taken from Part 66). The red view on the right is the ‘before’ photo viewing angle in Vincent et al., Figure 8. The yellow view is the ‘after’ photo’s viewing angle. The circa 100° change in viewing angle means that, in the ‘after’ photo, we’re viewing Ma’at 02 from the other side and from an ‘upside-down’ position. It should be noted that the right hand, red view is, confusingly, related to the left hand ‘before’ photo of Ma’at 02 in figure 8. And the left hand yellow view corresponds to the right hand ‘after’ photo in figure 8. 

The left hand ‘before’ version in figure 8 is what one might call the classic view, taken from above the head lobe. The right hand ‘after’ version is clearly from a different angle. One might at first think that the camera has been shunted towards the top of the frame with respect to the ‘before’ version. This is indeed the case but it’s been shunted so far that it’s gone right past the vertical point over the pit and on to a similar angle on the other side. 

So we’re looking at the pit from a completely different angle in the ‘after’ photo. Both views are around 40° from the local horizontal across the pit top. This was calculated from the fact that the pit is near-circular and the apparent length/width ratio is 0.6 or thereabouts in both photos. Sin-1 of 0.6 is 38° so let’s round it to 40° because it looks around 45° or just under. So the viewpoint has been rotated by around 180°- (40° + 40°) = 100° through a plane that arcs almost over the centre of pit to the other side. 

Since it ends up on the opposite side, the two views are in almost opposite directions, about 150° to each other when looking vertically down from above and into the pit. The 150° would therefore be the azimuth change which is rather like seeing the two viewing directions as two angled clock hands against the surface without being able to see that they also slope up towards us at around 40°, that is, sloping up in the vertical plane above the pit. 

Photo 4- the azimuth change. Red and yellow are at about 150° to each other when looked down on from above Ma’at 02. This isn’t quite directly above but high enough to show the azimuth change. 
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

This upside-down illusion was dealt with in more detail in Part 66. That part used two very similar photos of Ma’at 02, taken from almost the same two angles as the ‘before’ and ‘after’ photos in figure 8. One was the Ma’at 02 mosaic, taken by Rosetta on its final trajectory to its controlled crash-landing. This was stitched together by Rosetta blog commenter, Gerald. The other photo used was a classic NAVCAM view. Part 66 was primarily for context for people trying to make out the viewing angle for the stitched mosaic and alerting them to the fact that there was something of an illusion at play. It was pure coincidence that Part 66 uses two Ma’at 02 photos that are almost identical views to the Vincent et al. 2015 figure 8 pair, so Part 66 acts as a perfect primer to this part. It’s worth reading that part for an extra grounding although you can still follow this part fairly well without it. Neither photo 3 nor photo 4 above is from the pair used in Part 66 to illustrate the illusion. They’re old photos showing sideways and above views simply to demonstrate the 100° angle difference for the Part 66 pair and, by coincidence, for the figure 8 pair in this part. 

Returning to the figure 8 pair, the orientation of the ‘after’ photo has been kept the same way up in the frame i.e. no rotation has been allowed. This would be eminently practical for small movements in viewpoint but with a hike of 100° right over the pit, it means that the view is essentially upside-down. It could be argued that there’s no upside-down in space but this pair of photos is being presented to humans for comparison and humans have a built-in difficulty in recognising things that are upside-down or when they themselves have to turn upside-down to keep the subject the ‘right’ way up. This is what we are being asked to do before we start comparing the two views.

And of course, strictly speaking, on 67P there is an upside-down because there is some gravity. It’s probably around 2.5e-4 m/sec^2 at Ma’at 02. So, in photo 3, the lady’s hanging-down hair really would hang down if she were standing on a tower at the required viewing point. It would just take about a minute or a bit less for her hair to succumb to the weak gravity. 

Now, let’s say for argument’s sake that we were already used to looking at Ma’at 02 from this angle because we had all been schooled in viewing the whole duck-shaped comet in upside-down mode. That would be fine as far as it goes. But then the left hand photo of the pair would be unfamiliar instead. That’s our usual, familiar view and it would be deemed to be upside-down. Because we’re human and don’t like comparing things upside-down we object and try to flip them round (rotate them 180°). Part 66 goes into more detail on this. The only problem with rotating the ‘after’ version is that the two versions then face in opposite directions when put side by side for comparison. But at least that way we can start to discern the fact that we’re now viewing the pit from the other side, which has significant implications for the apparent changes described in the figure 8 caption. 

Photos 5 and 6- the figure 8 pair with the ‘after’ version (March 2015) rotated 180°.  
Photo 7- another photo with roughly the same viewing angle as the rotated ‘after’ version. This is photo 4 without the annotations. It gives more context of the surroundings showing that we are indeed now on the other side of the pit. Ma’at 02 is dotted blue
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Photos 8 and 9- these are the same as photos 5 and 6 but they’re festooned with fiduciary points that match across between the two. 

By toggling, you can start to see you’re looking at the pit from a completely different direction in the two photos. The biggest giveaway is the two red dips at the back of the pit in the ‘after’ (rotated) version. They can be seen in full 3D sloping down into the pit. In the ‘before’ photo, all you can see is the profile of the top rims and can’t see anything of the majestic troughs sloping down into the pit below the rim. The same goes for the pink dip. In the ‘after’ version, we’re looking directly at the back wall of the pit. In the ‘before’ version, we can’t even see the back wall of the pit because the viewpoint is way back behind that back wall. And of course, the reverse situation applies with the other side of the pit and this contributes to one of the errors explained below (the inclusion of the rugged terrace and cutting off the end of the flow).

Consequences of the two different viewing angles:

The flow in question undulates as it progresses away from the viewer in both versions of the figure 8 pair. It’s now easier to see this using photo 5 with the ‘after’ version rotated 180°. Any slope that was angled towards the viewer in the ‘before’ photo (September 2014) is liable to be somewhat foreshortened in the ‘after’ photo (March 2015) and vice versa. In fact, there’s one quite severe slope that runs across the field of view from left to right in both photos. Its left hand end in the ‘before’ photo is its right hand end in the ‘after’ photo and vice versa. The fact it runs across the field of view means that it’s very noticeable as a long, wide slope in the ‘before’ photo and much narrower (but the same length) in the ‘after’ photo. It’s angled very much towards us in the before photo so it’s somewhere near to square-on to the viewer. In the after photo it’s angled very much away from us. That’s what makes it look narrower. 

Photos 10 and 11- the sloping ridge that gets foreshortened. Outlined in white. 


Photo 12- shadowing of the sloping ridge proving the slope is quite marked. Just the two ends of the ridge are dotted white. This is Gerald’s stitch of the 30th September 2016 landing trajectory photo. It will be presented again below for another reason.

If the viewer doesn’t know about the angling of this slope they don’t realise that the entire flow is foreshortened along its length in the ‘after’ photo with respect to the ‘before’ photo despite the actual flow being unchanged. Without that knowledge, it’s reasonable to think that the flow has changed shape between the two photos. More importantly, if the flow as a whole has been foreshortened along its length in the ‘after’ photo due to the foreshortened ridge, it means by definition that the length-to-width ratio has been reduced which is another way of saying that the flow now appears wider. This is what the figure 8 caption says: “they seem to have expanded laterally”. We shall see below that there are two other factors that contribute far more to the lateral expansion illusion, but this foreshortening of the length due to the 100° difference in viewing angle also makes its own contribution, exacerbating the illusion still further. 

The foreshortened slope shown above is the most obvious one in the flow but there are several other less dramatic slopes. Combining them makes for a flow that appears to change shape and texture before our eyes over 6 months when in fact it hasn’t changed in any discernible way at all. If you laid tin foil on a table and crumpled it to a similar degree as the flow, it too would appear to change shape and texture if you viewed it from either side of the table. 


Header photos reproduced for easy reference. The ‘after’ photo is rotated 180° (not numbered).


The azimuth angle of the sun to the local surface across Ma’at 02 swings by around 130° between the ‘before’ and ‘after’ photos. This makes the shadowing noticeably different between the two photos and it has the effect of enlarging or diminishing the apparent size of otherwise unchanged features. This exacerbates the foreshortened slope issue described above, which leads to the flow being slightly foreshortened along its length dimension in the ‘after’ photo. 

Moreover, the lighting angle change allows the flow’s outer perimeter to creep, so to speak. Its edge is sharply delineated by shadowing in the ‘before’ photo because there’s a fairly steep-sided trough running along behind the perimeter’s leading edge. This is thrown into shadow in that photo. However, this trough is rather whited-out in the ‘after’ photo. This makes the flow and the smooth, dusty area beyond it look to be roughly on the same level as if the trough that had been shadowed in September 2014 has been smoothed out into the dust of Ma’at by a few metres. It would have to be at least a few metres in order to smooth the sharp, steep perimeter slope of the trough into a shallow, blended slope. This blending is again, an illusion. The reason we can be sure of this is that photos from much later, including Gerald’s stitch* of the mosaic (September 30th 2016, 18 months later) show that the flow perimeter has apparently returned to its old September 2014 shape and position, i.e. contracting from the apparently spread-out, washed-out version of March 2016 and remembering its old shape. This is of course impossible so if September 2014 and September 2016 look the same it means the peregrinations of March 2015 never really happened and are a trick of the lighting. 

*To allay any fears that Gerald’s stitching process may have caused anomalous artefacts in the outer perimeter shown, we can see it along with the relevant unstitched mosaic component below it. This shows that no stitching was required in the actual flow area because the entire flow was caught within one mosaic frame. 

Photos 13 and 14- photo 13 is photo 12 reproduced: Gerald’s stitch of the 30th September 2016 mosaic component of Ma’at 02. Photo 14 is the relevant mosaic frame. Gerald’s stitch shows the flow looking essentially the same as it did in the Vincent et al ‘before’ photo that was dated September 2014, two years before.

In photo 13 (September 2016) the flow may be completely unchanged from two years before, in September 2014 or there may be some as-yet unidentified changes. But just like the Vincent et al ‘after’ photo, the viewing angle is on the wrong side of the pit for making subtle comparisons with the ‘before’ photo. However, the point being made here is that seeing as the view is on the same side as the ‘after’ photo (March 2015) it can be compared with that photo and it looks substantially different from it. This might suggest at first glance that change really was afoot but, on closer inspection, it’s different in such a way that makes it strikingly similar to the September 2014 ‘before’ photo. This suggests the flow never did change up to March 2015 (the ‘after’ photo) and that the changes in that photo are an illusion. 

The extent to which the 2016 mosaic frame is similar to the ‘before’ photo and different from the ‘after’ photo is entirely consistent with the illusions caused by the three points being presented here: viewing angle, lighting angle and ellipse placement. These three factors aren’t simply presented here as general confounding issues. Further below, we shall carve out the exact anomalous chunk from the ‘after’ photo that arises from the lighting illusion and also add in a section that arises from the foreshortening illusion. As a result, we shall end up with the true shape of the flow itself in the ‘after’ photo, which will turn out to be the same shape and size as depicted in the ‘before’ photo. 

The creep issue, related to the lighting angle change, also applies to other lumps and dips within the flow and its this creep that exacerbates the foreshortened slope issue, extending and retracting the periphery of each lump and dip. The outer flow perimeter just happens to be the most obvious example of this because it’s a continuous dip or trough, meandering along the perimeter and is set against the smooth, untouched dust of Ma’at. It’s easy for the lighting angle (from above the head lobe) to illuminate the trough in the ‘after’ photo and thus blend it into the smooth dust as if it has spread out. When lit from the other side, as in the ‘before’ photo and also the mosaic photo, the trough reappears markedly. It reappears either side of March 2015 (i.e. in September 2014 and September 2016) proving the blending illusion in the ‘after’ photo. Nothing has changed in any discernible way over the two-year mission. 

Photos 15 to 17- the outer perimeter of the flow is well-defined by the same lighting angle in both September 2014 and September 2016 but whited and smoothed out in March 2015. 

Copyright: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA. For photo 16 (Sept 2016) stitching credit: GERALD

In photos 15 and 16, the trough running along just inside the perimeter is in shadow. However, the perimeter is whited out in photo 17 (March 2015) due to lighting from circa 130° towards the opposite direction. This illuminates the trough, giving the impression that the flow perimeter has spread out further into the dust of Ma’at.  

The illusion of the blending of the perimeter into the Ma’at dust is greatly exacerbated by the misplacing of the white, dotted ellipse in the figure 8 ‘after’ photo. The ellipse perimeter ends up around 20 metres closer to this apparently blended perimeter line, thus giving the illusion that the already non-existent blending extent is 20 metres and not a few metres. This ellipse placement error is discussed in more detail under its own heading below. 

The circa 130° lighting angle change also results in a substantial area of the actual pit being illuminated so brilliantly that it appears not to be in the pit but on the rim. This is by far the greatest illusion between the ‘before’ and ‘after’ photos. From the figure 8 caption statement, “and they [the flows] seem to have expanded laterally”, it appears that this illusion has gone unnoticed. The authors have added the section that’s inside the pit in the ‘before’ photo to the rest of the flow in the ‘after’ photo. The section in the pit clearly isn’t part of the flow in the ‘before’ photo but again, because of white-out from much higher illumination, the lumps and dips in this area of the pit get smoothed together in the ‘after’ photo. In addition they’re apparently smoothed into the flow, increasing its width. But the smooth area of the flow actually starts on the true rim, about twenty metres above all these rugged bumps and dips. Their rugged nature betrays their true nature: they’re consolidated material sitting on a terrace, below the pit rim and therefore very much inside the pit. 

Photos 18 to 20- the rugged terrace perimeter is pale blue and the true pit rim is pale yellow. Other colours are fiduciary points: three light blue boulders, a fuchsia crack (not visible in the ‘before’ photo due to the 100° viewing angle change) and a dark blue ridge. These fiduciary points aren’t in photo 18 but are in its reproduced version in photo 25. 


Much work went into identifying the pale yellow rim across the apparently featureless ‘after’ photo. This was done using the ‘before’ photo as a reference for finding fiduciary points along the rim line (those fiduciary points are not shown here). Also, these fiduciary points on the ‘before’ photo were cross-referenced with other Ma’at 02 photos for confirmation. Photos were annotated with the yellow rim fiduciary points including the ‘before’ and ‘after’ photos. The after photo does exhibit enough faint features to catch the rim line. These photos will be added in an appendix in due course for completeness. However, if you look hard enough at the originals (using the annotations only as an initial guide), you can see the rim on the after photo. It takes some time though. 

UPDATE (INLINE APPENDIX- 5th November 2016)

As promised above, here are the photos with the fiduciary points for the pale yellow rim line. They’re in the following order with an ‘A’ for Appendix. 

A1-‘before’ photo with different, coloured dots acting as fiduciary points sitting on specific features (shape vertices and lines) near the pale yellow rim and across the flow area. 

A2- before photo ‘original’ but this is actually a zoomed in crop of an earlier version which still has the other annotations but is missing the ones dotted near the rim and on the flow as in A1 above. 

A3- the ‘after’ photo with the same coloured fiduciary dots as A1, i.e. placed on the exactly the same features near the rim and on the flow. 

A4- the ‘after’ original in the same manner as A2 is presented for the ‘before’ photo. 

A5- Gerald’s stitch with the same fiduciary points.

A6- Gerald’s stitch (original).

Key for the fiduciary dots on all three photos follow.

Light grey, brown, beige and slate blue single dots denote tips of pointed sections on the outer flow perimeter. Brown is more elusive than the rest.

Yellow- this nestles at the tip of a triangular set-back at the top of the slope and at the back end of one of the ‘fat tip’ areas. See further down for the fat tips. 

Green- this sits at one end of a small, smooth, straight section. The section is a narrow rectangle and other end of this rectangle is the slate blue tip. The width of the rectangle separates the fat tip area (whose apex is the slate dot) from the slope. 

Two dark blue dots- these sit on the two tips of a a swallow-tail feature at the back end of the area that leads across to the beige-dotted tip. The after photo shows the whole length of this area, from blue pair to beige as being one distinguishable area due to the apparent sweeping direction of the flow between them. This is partially apparent in the other two photos as well. 

Terracotta- a single dot along the sweeping flow between the blue pair and beige. This denotes a dip. 

Curving slate blue line- this is an obvious majestic curve. 

Light mauve- adjoining the slate blue line, this is a zig zag line. 

Fuchsia outcrop- this is actually part of the original annotations. The pale yellow line shows it consistently sitting inside the pit on the correct side of the rim. However, without any annotations, the outcrop apparently jumps out of the pit in the ‘after’ photo and sits perched on the rim with two sides bordering the flow. In the ‘before’ photo, just the tip of the fuchsia outcrop can be seen and it’s clearly in the pit. In Gerald’s photo, more of it is visible because it’s the same viewpoint as the after photo. It certainly looks more in the pit than out. The tip is in the pit, as for the ‘before’ photo and the rest is forming the pit sidewall, i.e. it’s inside the rim. 

The crucial point here is that Gerald’s photo and the after photo are from the same viewpoint and yet the everything left of the pale yellow line in Gerald’s is in shadow beyond the rim. This is in complete contrast to the ‘after’ photo that apparently shows the same area to the left of the pale yellow line as being just an ordinary continuation of the flow. It appears to be at about the same level as the rest of the flow, continuing on to a rim that would be about a third of the way across Gerald’s pit. The obvious drop-away into the pit in this portion of the ‘before’ photo shows that this can’t possibly be part of the flow. It therefore corroborates Gerald’s shadowed area that suggests a sharp drop-away too. So it’s clear that the area to the left of the pale yellow line in the ‘after’ photo is in the pit, beyond the rim, and yet appears to be part of the flow above the rim. 

All the fiduciary points marked in A1, A3 and A5 are apparently much further from the pit rim in the ‘after’ photo even though they have been very carefully placed on the same features. The most obvious example is the pair of dark blue dots on the swallow tail. The swallow tail is definitely right on the pit rim. And yet it’s apparently marooned in the middle of the flow in the ‘after’ photo. This is further corroborated in photo 18. The blue dots aren’t marked but the swallow tail tips can be made out fairly easily. They’re at the 8th and 13th pale yellow dots from the bottom. According to the ‘after’ photo, these two dots should be right out in the middle of the flow. And yet they’re on the rim in photo 18 as well.

UPDATE 2 (same date)- I decided to annotate photo 18 with the swallow tail dots after all. It’s important because identifying the shape of the swallow tail precisely, allows us to clinch the argument for the tail being apparently in mid-flow in the ‘after’ photo but on the rim in the before photo.
Photos A7 to A10 are variations on photo 18. 
A7-shows two larger dark blue dots on the central areas of the two fins of the tail and two small blue dots at the fin tips. It also shows the beige pointed tip and the terracotta dip (whited out). 
A8- shows the same as A7 but with the perimeter of the shape that’s obvious in the ‘before’ and ‘after’ photos as an identifiable shape in the flow- almost like an embedded mini-flow. With a swallow tail and a beak, it doesn’t quite look bird-like but it is a characteristic shape that can also be discerned in the ‘before’ and ‘after’ photos. Notice the characteristic, curved dip between the two fins that is especially visible in the ‘before’ photo, sitting right on the rim and just visible in the ‘after’ photo. 
A9- photo 18 reproduced to allow a dot-free analysis of the swallow tail while still having the pale yellow rim for guidance. 
A10- the true original with no dots for a completely dot-free analysis of the swallow tail and rim. 
The upper fin in A7 to A10 stays resolutely on the rim in all photos. The lower fin in A7-A10 appears to drift from the rim and across the flow by a few metres when viewed in ‘before’, ‘after’ and Gerald’s stitch. This is probably due to the A7-A10 photo being very well-lit and the other photos being subject to the same shadow-drift or ‘creep’ anomaly as described further above. However, the drift is small and it’s just one part of the whole swallow tail, which as a whole, is on the rim in the ‘before’ photo and halfway across the flow in the ‘after’ flow. 

Photos A7 to A10
And finally for this update, the ‘after’ photo with the same shape in beige with original (A11 and A12). Fins are in the centre of the flow.


Photo 18 is another one of the last photos of Ma’at 02, taken during the landing phase and it’s a very good overhead shot. Photos 19 and 20 are our usual ‘before’ and ‘after’ photos and the originals for all three follow them. The area enclosed by the pale blue and pale yellow lines is the same in all three photos and is the rugged terrace area. It’s the same area even though it changes shape due to the very different perspectives. There’s also some shadowing of the area in the ‘before’ photo. In that photo, the light blue dots turn to a darker blue in the shadow to show it’s an estimated line. And there’s some obscuration of the rugged terrace by the rim in the ‘after’ photo. This area enclosed by the pale blue and pale yellow lines, the rugged terrace, has been added to the flow area, in error, in the ‘after’ photo, March 2015. 

The spurious addition of the rugged terrace to the flow greatly increases the apparent width of the flow in the ‘after’ photo when compared with the ‘before’ photo. This illusion certainly would lead us to believe that the flow had “expanded laterally” when in fact it remained unchanged. 

The additional area taken up by the rugged terrace is on the opposite side to the outer perimeter that appears to be blended by 20 metres due to the ellipse border being placed 20 metres closer to the perimeter than in the ‘before’ photo. This means apparent width has been added to both sides of the flow. So with the inclusion of the rugged terrace, the apparent extension of the width of the flow is even greater. 


Photos 21 to 23- the misplacing of the ellipse. Photo 21 shows the ‘after’ ellipse superimposed over the ‘before’ photo, showing the discrepancy. Photos 22 and 23 are the originals with their respective ellipses for comparison. 


Further below we shall see how the ellipse crosses the outer flow perimeter in a different place in the ‘after’ photo from its crossing point in the ‘before’ photo. However, the most important things to note in the meantime are:

a) the inclusion of the rugged terrace by shunting the ellipse over into the pit in the ‘after’ photo.

b) the noticeably narrower area of smooth dust enclosed between the outer flow perimeter and the ellipse perimeter in the ‘after’ photo. as compared with the wider area of smooth dust enclosed in the ‘before’ photo. You can use the terracotta dots as a guide so you know what it is you’re looking for but then it’s best to toggle between the two original white-dashed ellipses to see this different-size area of smooth dust outside the flow perimeter. The markedly narrower area in the ‘after’ photo is enclosed between the 9 o’clock point and (almost) the 12 o’clock point on the white ellipse.

Photos 24 and 25- photo 24 is photo 18 reproduced. It shows the rugged terrace from overhead. Photo 25 shows the crucial part of the ‘after’ photo ellipse projected onto photo 24. The original follows. No apology is made for the weird ellipse shape. It follows the fiduciary points impeccably and is thus shaped due to the fact that the ‘after’ photo ellipse was projected onto different topographical layers (pit rim and pit base) causing parallax, and projected from a substantially different direction. 


Pale yellow- the pit rim as depicted very obviously by shadowing and topography in the ‘before’ photo (see the fuller description further below). 

Pale blue (medium size)- the perimeter of the rugged terrace, which is low down in the pit. The official term in the OSIRIS papers for ‘rugged’ is ‘consolidated material’ which is considered as being rocky in appearance, presumably comparatively solid (consolidated) and without any dust covering. In other words, consolidated material is wholly different in nature from granular flow that has to comprise dust and grit by definition. 

Pale blue (small)- the very small pale blue dots denote the best assessment of the bottom of the slope that runs between terrace and rim. This slope is also rugged and is shown here to be part of the area that’s been added to the flow area in the ‘after’ photo. In that sense it should be considered as being part of the rugged terrace for our purposes: a rugged area that’s been mistaken for a smooth, flowing area. 

In photo 24, the true pit perimeter is dotted pale yellow. This is the same line for the rim as is strongly suggested in the Vincent et al. 2015 ‘before’ photo. In that photo, this line is the dividing line between the obvious flow-like features bordering the rim and the steeply sloping, rugged terrain that drops away into full or partial shadow. The difference in terrain type either side of the rim (flow versus rugged) is very obvious in both photo 24 photo and the ‘before’ photo. However, it’s not at all obvious in the ‘after’ photo where the rugged terrace, including the rugged slope, is included and is assumed to be part of the flow. 

The spurious addition of the rugged terrace in the ‘after’ photo means that the rim of the Ma’at 02 pit has been misidentified in that photo whilst it’s been correctly identified in the ‘before’ photo. This leads to the ellipse being shunted over by about 20 metres, possibly 30 metres, in the ‘after’ photo. It’s shunted right into the pit area in the belief that the perimeter of the ellipse is just about enclosing the pit rim and therefore the flow perimeter that starts at the rim. But the ellipse perimeter is in fact enclosing the rugged terrace that’s well inside the pit.

Since the ellipse gets shunted by 20 or so metres on the pit side, it also gets shunted by the same amount on the other side at the outer perimeter of the flow. Otherwise, the ellipse would get fattened into a circle and the shunting error would be noticed immediately. 

This shunting means that the point at which the ellipse crosses the outer perimeter of the flow is further along the perimeter in the ‘after’ photo than in the ‘before’ photo. This discrepancy is about 20 metres which is roughly commensurate with the rugged terrace width of around 30 metres. 

The ellipse doesn’t only cross the outer perimeter of the flow 20 metres too far along. It also gets placed about 20 metres closer to the unchanged flow perimeter. This means there’s a 20-metre-narrower area of unblemished dust between the flow perimeter and the ellipse than in the ‘before’ photo. This is done in error and for no good reason. The viewer can’t help but look at the flow perimeter being substantially closer to the ellipse perimeter in the ‘after’ photo and assume that it has crept towards the ellipse perimeter by that amount between September 2014 and March 2015. But the simple truth is that it’s the ellipse perimeter that has crept towards the unchanging flow perimeter by virtue of being misplaced. 

This apparent movement towards the ellipse perimeter is exacerbated by the blending illusion described above where white-out in the ‘after’ photo seems to smooth the trough along the perimeter further out into the dust. 

When trying to identify changes with a +\- error of 2 metres, a 20-metre ellipse placement error is an order of magnitude greater than the error bars. This is in addition to the mistaken inclusion of the rugged terrace. Including the circa 30-metre-wide rugged terrace in the flow adds up to 50% to the flow’s width (50% across its central width, 10-40% either side- see below). This completely skews its apparent shape, rendering the comparison of the ‘before’ and ‘after’ photos in figure 8 completely useless. This is of course unacceptable.

Recapping the figure 8 caption in Vincent et al. 2015, it says:

“Top panel: flows from Ma’at regions between two of the active pits have changed; their outline is different and they seem to have expanded laterally.”

The changes in the flow are stated as fact in the caption whereas the analysis in this post shows there are no discernible changes in the flow at all. 

The statement above should be withdrawn along with the photos and an erratum issued for this paper regarding the certainty of ongoing granular flow or indeed any granular flow, ongoing or historical, on the comet. 

We’re still left with the hypotheses that granular flow may well have happened in the past but that is all. 


Photos 26 to 28. This is a sequence of three annotations showing essentially the same two things: (1) the extent of the rugged terrace area that was added and (2) the circa 20-metre section of the outer flow perimeter that was cut off the end. This sequence of pairs is the original header without the ‘after’ photo flipped. This is so as to compare the flow shape more easily in the context in which it was originally intended to be appreciated in figure 8, along with its caption. 


Photo 26 shows the before/after pair with the flow shape perimeters dotted in red as the viewer can only be expected to perceive them, given the visual cues and the explanation in the figure 8 caption. 

Photo 27 has the ‘after’ photo showing the true perimeter of the flow without the rugged terrace included. The ‘before’ photo is unchanged because it never included the rugged terrace nor was it truncated along its outer perimeter. You can now see the extra chunk of the flow that was cut off due to the 20-metre error. It’s encroaching into the ‘before’ photo because it was cut right out of the ‘after’ photo. 

Photo 28 shows the rugged terrace area in pale blue just to show how much area had to be removed in order to show the correct area of the flow. The measurement across the pinched central dimension of the true flow area is the same as the widest part of the rugged terrace area. This means the flow area’s width was doubled, no less, across its central dimension. It’s no wonder the flow looks like a fat rectangle in the ‘after’ photo. Its true, pinched shape is hiding in plain sight within the whited-out area. 

The 20-metre cut-out is shown in pale green in photo 28 as well. 

It should be stressed that, as with the rim perimeter of the flow, the true outer perimeter isn’t guessed. It’s been meticulously researched using several photos and by matching fiduciary points between them. This was needed to understand exactly where the ellipse crosses the outer perimeter in the ‘before’ and ‘after’ photos. 


You may wonder how different points on the the outer flow perimeter could be misidentified, since certain wavy sections look fairly obviously the same in both photos. However, there are also two different sections that look uncannily similar in both photos. The manifold illusions described above have resulted in a particular fat, pointed area on the flow perimeter in the ‘after’ photo being mistaken for the next fat, pointed area along in the before photo. That next area is highly visible in the ‘before’ photo and is at the true end of the flow. It’s the fat point that should have been chosen in the ‘after’ photo but it’s hardly visible there for reasons laid out below. The incorrect fat point that was ultimately chosen is the first one along from the true end point. It was probably chosen because it was:

a) the first discernible point along the perimeter in the ‘after’ photo. This was due to white-out and foreshortening of the true, first point.

b) this second point is roughly the same shape in the ‘after’ photo as the first point in the ‘before’ photo. 

Photos 29 to 31- the five fat points along the outer perimeter of the flow. The dots in photo 29 are just outside the tips of the points. Photo 30 shows the notional fat bodies of the points. Photo 31 shows them named ‘a’ to ‘e’. It should be noted that the light grey dot is sitting just inside its fat body and on the inside of its point tip. That’s because the rounded point tip is off-frame. The rounded tip is very obvious in all the other photos so it’s easy to judge that it’s only just off-frame. 

Incidentally, this being another September 2016 landing trajectory photo, it was taken within about an hour of Gerald’s stitched mosaic. Again, you can see that the outer perimeter, as defined by the coloured dots, is remarkably similar to the September 2014 ‘before’ photo perimeter. There are white-out issues in places but you can just about see the same line. 

It was d in the ‘after’ photo that was mistaken for e in the ‘before’ photo. e is the true last point at the end of the flow. e’s point is pink but e has a white perimeter because it comprises the sloping ridge mentioned above that’s already dotted white. Yellow and green are fiduciary points for other photos that may get added later. 

Incidentally, there’s a triangle between c and d that exhibits slight flow-like appearance but it’s less marked than the fat points along the rest of the perimeter. It was left out from being annotated in all three photos because it’s confusing in that it’s more apparent in some photos than others. The main thing is that it is there in all three photos and doesn’t change in any discernible way. That is itself one small additional piece of evidence for the flow not expanding laterally as claimed. 

This mistaking of d for e along the perimeter was possibly an error that was forced by the exigencies of moving the ellipse further over into the pit which was itself an error. In other words, it’s an error that might not otherwise have been made. However, if you were ever going to mix up two of the points along the outer perimeter, it would be these two. This is because the misidentified point, d, sits right at the top of the well-defined slope described in (1). That’s the white-dotted slope that’s much-diminished in the ‘after’ photo due to foreshortening. The correct fat point, e, is at the end of the flow perimeter. It’s perfectly visible in the ‘before’ photo and, crucially, its fat area (next to its actual pointed tip) comprises the very slope in question, the foreshortened slope. So, when trying to identify point e in the ‘after’ photo, it’s not there or it’s so hidden by foreshortening that it’s not very easy to see at all. This is compounded by the different lighting angle that whites out the sloping ridge anyway (it’s directly facing the sun) and smudges any vestige of the ‘e’ point because the ‘e’ point itself comprises the sloping ridge. In fact, the e point was so elusive that it was cut right out of the ‘after’ photo.

Photos 32 to 34- photos 32 and 33 show the foreshortened white ridge in relation to the fat points numbered a to e. You can see how the ridge comprises e and also that e’s shape in the fig 8 ‘before’ photo looks similar in shape to d’s shape in the ‘after’ photo. Photo 34 is Gerald’s stitch again, showing a similar angle to the ‘after’ photo but from a bit lower down.

Gerald’s photo shows the e fat-point perimeter in white (i.e. the end of the foreshortened ridge). This is somewhat guessed but that upper, white portion is nevertheless fairly accurate because there’s a faint white streak beyond it, leading to a double-bumped, pointed outcrop beyond. Those fiduciary features are just about visible in the ‘before’ photo and are foreshortened in that photo due to the 100° viewing angle change. In the ‘before’ photo, the white streak is almost invisible to the right of the dotted ellipse (and may admittedly be an artefact of the ellipse-dotting). The double bump, however, definitely does have highly foreshortened terrain between it and the bottom of the sloping ridge. Since we’re looking into a U-shaped dip in both photos, the white ridge is fairly square-on in the before photo while the white streak and outcrop are foreshortened. And conversely, in the after photo, the white ridge is foreshortened while the streak and double bump are more square-on. This apparently mind-numbing detail will help us greatly in understanding the stretch theory explanation for the flows, coming out soon. 

One might say that the features either side of this wrongly chosen point (which is point d at the top of the slope) should have shown up the error. However, the white-out and creep issues described above for the ‘after’ photo cause the fat area of the d point in that photo to mimic the shape of the e point area in the ‘before’ photo. The e area (sloping area) is perfectly visible in the before photo but now all but disappeared in the after photo, with its tip actually disappeared, off frame. If you hunt for it without knowing it’s disappeared you are liable to pick this same-shaped d area that’s actually the next area along, starting at the top of the slope. 

Just to complicate matters further, the somewhat larger, flat area that’s visible on the other side of this wrongly chosen d area in the ‘after’ photo, does apparently match between the two photos and is apparently correct. How can this be if the correct area (area e) is between the two? Again, it’s because area e has all but disappeared due to the foreshortening and white-out effects. This allows the area at the top of the slope to appear to join seamlessly to the larger area at the bottom of the slope. But the large area at the bottom of the slope has area e between it and area d at the top of the slope. 

The ‘after’ photo ellipse therefore cuts the outer flow perimeter off at the second-to-last fat point tip (the tip of area d), which is about 20% of the way along the perimeter length from e, thus shortening the flow’s outer perimeter length dimension by 20%. But since the ellipse is supposed to be showing the same area (because it crosses what is thought to be the same place as in the ‘before’ photo, point e), we’re led to believe that the outer perimeter length presented within both ellipses is the same. But the the flow perimeter in the ‘after’ photo is missing 20% of its length while masquerading as the full-length flow. This might seem automatically to result in an apparent 20% apparent extension in width by virtue of the law of proportionality. This is without even the addition of the rugged terrace. It’s probably more like 10% owing to the vicissitudes of the 100° difference in viewing angle.

Once this notional 10% is factored in, we still have the fact that the ellipse perimeter is 20 metres closer to the flow perimeter in the ‘after’ photo leading us to believe that it’s the flow perimeter that has crept towards a stationary ellipse by 20 metres. But the flow perimeter has stayed rock solid within the bounds of discernibility. 

The 10% is a length-to-width proportionality illusion. The 20-metre creep towards the ellipse is a translational shunt illusion. The foreshortened length due to the foreshortened slope is a also a length-to-width illusion. The rugged terrace is an actual inclusion of a real area, widening the flow even more. All four illusions work together to widen the flow substantially between September 2014 and March 2015. But in reality it remained unchanged. 

And indeed, it appears to have remained the same right up to the very last photo taken of Ma’at 02 in September 2016. 

This is notwithstanding further scrutiny of all the available photos on a much finer scale (at the same level of resolution as was conducted in this post) but using photos with similar viewing angles and lighting. I haven’t had the time to do this because of having a backlog of posts on other areas of the comet.  


This post has studied the ‘before’ and ‘after’ photos in the upper pair in figure 8 of Vincent et al. 2015. By analysing them at the 5- to 15-metre scale, it has been found that there were no discernible changes to the so-called flows between September 2014 and March 2015. This is in direct contradiction to the figure 8 caption which states:  

“Top panel: flows from Ma’at regions between two of the active pits have changed; their outline is different and they seem to have expanded laterally.”

It would be appropriate here to make a comment about the scale at which OSIRIS appear to be analysing the comet and the scale at which Marco Parigi and I are analysing it. Although OSIRIS have a shape model that’s accurate to the 5-metre scale, the photos in the OSIRIS papers are rarely analysed or annotated at a scale of less than 50 to 100 metres. In contrast, Marco and I consistently analyse the comet at the 5- to 15-metre scale, zooming right out to the 100m scale or more for context, then zooming back in to the 5- to 15-metre scale again for continuing the analysis on the adjacent area. This is reflected in our blog posts and our photo annotations. 

It would have been impossible to find the fiduciary points necessary to ascertain no change in the Vincent et al 2015 photo pair without employing this method and doing so using multiple photos from different angles (including many not actually reproduced in this post). This necessitated 34 annotated photos and 6000 words. This is because the flow area was scrutinised at the ~10 x 10 metre scale, meaning the flow was potentially divided into about 100 small areas instead of one big area (i.e. what was enclosed by the ellipse in figure 8). Around 20 of these smaller areas were shown via annotation and at least as many more were ascertained for orientation purposes but not used in the post. 

It’s therefore impossible to describe the shear intricacy of the Ma’at 02 pit in 23 words and two photos as figure 8 attempted to do. 

This assiduous approach to our analysis is why the four corrections I’ve made to OSIRIS papers to date (including this post) aren’t serendipitous finds. It’s borne of a rigorous analysis of almost the entire northern hemisphere down to the 5- to 15-metre scale. The same goes for Marco’s recent correction of the El Maarry et al. 2016 OSIRIS paper regarding the placing of the Anuket/Sobek border and notifying them of a cliff collapse. I made two further corrections in that paper (counting together as one of the four corrections mentioned above). All these corrections in El Maarry et al. 2016 were kindly acknowledged and corrected. One of the other two corrections I made for other OSIRIS papers was also acknowledged and corrected. 

I’m therefore loath to criticise sharply because Marco and I want to continue to be of help. However, it has to be said that, until the comet is scrutinised assiduously at the 5- to 15-metre scale, its morphological evolution won’t be understood. Analysing at this scale doesn’t furnish us with the last 5% of understanding; it furnishes the first 95%. It’s why this, the stretch blog, and Marco’s blog are currently well-advanced in understanding the evolutionary morphology of 67P. There are many additional discoveries of sub-mechanisms that drive morphological change and that have followed on naturally from what is now a nuanced understanding of the main stretch mechanism. A number of these sub-mechanisms are already documented in the previous 66 parts. Several more are still to come, along with dozens of parts showing examples of how these sub-mechanisms dramatically reshaped specific features. 


Part 52

Part 62 (click through to Parts 63 and 64)



Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

To view a copy of this licence please visit:

All dotted annotations by A. Cooper. 



Part 66- The Final Approach Ma’at 02 mosaic 




This post is concerned with the viewing perspective of one of the last photos taken by Rosetta as she approached the comet on her controlled crash trajectory. This occurred on the 30th September 2016 at about 10:20 UTC and the photo was of the pit called Ma’at 02, which was the focus of Parts 62 to 64. The mosaic in the header is in effect a single photo of the area around Ma’at 02 and in this sense it’s is a bit confusing because the constituents are overlapped. It’s even confusing once it’s been stitched together because we’re looking at Ma’at 02 ‘upside-down’ in relation to the usual views we have of this pit. It’s something of an illusion and will be explained below. 
Ma’at 02 is also known as Deir El-Medina. That’s its recent new name but its still referred to as Ma’at 02 for clarity and brevity on this blog.

The upside-down illusion regarding Ma’at 02 will be crucial in understanding an upcoming post which is to do with two similar photos of Ma’at 02 that were used in a scientific paper. 

For readers wondering what happened to the rest of the Ma’at pit delamination series, this will be resumed in due course with at least two more parts to add to the three parts mentioned above, 62-64. They will be presented with a reminder that all five are linked as a series. 


Photo 1- the mosaic (header reproduced).


The mosaic of Ma’at 02 is essentially a radially exploded photo. The pit is in the middle and every photo to the left, right, up and down overlaps with the last one towards the pit at the centre as you progress to the edge of the frame in four directions. Put another way, if you cut out all the photos and then concertinaed them together carefully so there were no overlaps, you’d see a single, faithful image of the pit and its surrounding terrain (see photo 2).

Photo 2 (2nd header, reproduced)- this is a stitching together of the constituents of the mosaic as described above. H/T to Gerald, a Rosetta blog commenter, for doing this so neatly. Gerald did just the stitching. All later annotations on this stitched version using coloured dots are mine, and of course the usual ESA/OSIRIS credit applies for the photo mosaic itself. 


It might seem as if that’s that and we can move on to other things. After all, if we toggle between the stitched view and the classic overhead view of Ma’at 01, 02 and 03 that was presented in Parts 62-4, the two seem to look as if they’re from a similar perspective, one viewpoint tipped up just a bit with respect to the other:

Photos 3 and 4- toggling between the stitched and classic views. Ma’at 01, 02 and 03 are dotted blue and 02 is in the middle. 



However, looking more carefully, we can see that the stitched viewpoint is actually upside-down when compared with the usual ‘upright’ views we get of Ma’at 02. 

These classic views are shown in photos 5 to 7. They’re classic in the sense that the duck-shaped comet is upright i.e. in ‘upright duck’ mode with the head lobe above the body lobe. 

Photo 5- this is a NAVCAM photo taken from above the head lobe.
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER
Ma’at 02 is marked with a single light blue dot in photo 5. This photo shows the head rim as being brighter than the body which helps differentiate the two. The differentiation is less clear in photo 6, which is almost the same view but more detailed because it’s an OSIRIS photo. 

Photo 6- another one from above the head lobe. The toggling view in photo 4 is a close up of this photo. Ma’at 02 is light blue again. 

Photo 7- the classic side view. 
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

Photo 8- this is the photo 7 view with the two viewing perspectives from photos 3 and 4 superimposed.
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

As you can see, the two views are wildly off with each other, over 90° in fact, and certainly not similar viewpoints. We haven’t gone ‘upside-down’ yet so it might appear a bit confusing until you get to photo 10, which comes soon. 

Red is the classic overhead viewing direction or vector (the viewpoint in photo 3) and yellow is the stitched view (photo 4). Arrows show the direction of viewing. 

Since we’re viewing both vectors from almost overhead, it’s not showing the vectors’ angles with the surface (~40°) so much as their angle to the latitude and longitude lines of the comet if those lines were superimposed. The angle with the local average surface is known as the altitude angle and the angle with the lat/long lines is known as the azimuth angle. So photo 4 shows primarily the azimuth angles. But since we’re off to one side slightly (to the left) we can see under the two lines just a bit which betrays a little of the altitude angle. Photo 9 shows the altitude angles very well. 

Photo 9- this is a side view which shows the altitude angles of both viewpoints. Yellow is the viewing vector for the stitch. Red is the viewing vector for the classic top-down view. 
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

But it doesn’t quite end there. Photo 10 gives the true viewing orientation as we look at Ma’at 02 along the yellow stitch vector (and the classic red view for comparison). 

Photo 10- The viewer’s position is upside-down. 
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

This means that what looks like a similar viewpoint in photos three and four is only apparently similar and in fact 100 degrees off. 

Understanding the capacity for this Ma’at 02 perspective phenomenon to trip us up will be crucial to the next part. It’s going to be instrumental to showing that evidence for recent morphological changes, presented in a scientific paper, is just a mirage.


Photos 11 and 12- photo 11 (top) is the stitched version rotated 180° to the classic upright duck orientation. It now appears very close to the viewpoint of the classic side view (photos 7 and 16, below) but a little lower because you can see under the ledge that’s somewhat below Ma’at 02. Photo 12 is the original upside-down stitch, included for toggling.
Photos 13 and 14- this is just the pit, Ma’at 02. Photo 13 (top) is the original stitch, unrotated and photo 14 is the classic top-down view from photo 4. They look uncannily similar despite being viewed from completely different angles. 

Photos 15 and 16- photo 15 is the stitch, rotated, and photo 16 is the classic photo 7 view.

This pair shows that the views are now almost the same just by rotating the stitch to the familiar ‘upright duck’ view. This is the equivalent of inviting our upside-down lady in photo 10 to stop hanging upside down and view Ma’at 02 down exactly the same viewing vector but sitting ‘upright’ like the rest of us. 



Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

To view a copy of this licence please visit:

All dotted annotations by A. Cooper. 



Part 65- OSIRIS Map Anomalies and Corrections



The lead author of the relevant paper in this post, Ramy El Maarry, kindly acknowledged my comment in the Rosetta blog post thread linked lower down, and agreed to three of my four main points regarding these anomalies  (including the Anuket neck border anomaly that Marco Parigi had also highlighted). He has sent an erratum to the publishers and put our names in the acknowledgements for the paper for which we are most grateful. 

Ramy also explained very comprehensively the other four apparent, minor anomalies some of which I had suspected were intentional OSIRIS map changes rather than anomalies. His comment, in answer to mine is linked here:

And of course, he kindly answered Marco’s comment with his Anuket anomaly too and that comment is further down below the one linked above. He also acknowledged Marco’s important discovery of a recent rockfall at Anuket. 



This post is regarding the OSIRIS maps presented in this Rosetta blog post:

There are several errors in the maps. These were outlined by me and by Marco Parigi in the comment thread for the above-linked post. I found eight errors and Marco found one of them independently. Our two comments are linked at the bottom of this post and mine is reproduced in full a little further below here so that you can refer back to it and mentally tick off the eight points as they’re corrected in this post.

Marco’s find was one of the more large-scale and therefore important anomalies. He has already done a blog post on it so I won’t have to address that particular one here. It concerns the Sobek/Anuket border being placed a few hundred metres apart in different renditions (or viewpoints) of the map. Link here:

Marco’s post corresponds to my point 3 in the first list of four in my comment.


(This is reproduced in full for clarity. However, you can skip it and go straight to the separate points of the comment that are addressed below it).

Hi Claudia

I’ve identified several rather important contradictions on the maps presented in this post as well as several smaller contradictions. The more important contradictions are:

1) While Bes is clearly marked in the first map it disappears in the second one, taken over by Geb and Anhur. It’s not perspective, you can see the same features coloured differently. 

2) In the montage, right hand column, middle image, “Seth” and “Babi” are actually “Anhur” and “Bes” respectively. 

3) On the third map, Anuket is shown including the second heavily shadowed scarp along its border with Atum and even incorporates the third (non shadowed) scarp. These two scarps are incorporated into Sobek in the fifth map. In that map, the border kisses only the first scarp which is the scarp where Vincent et al’s jets 27 and 31 were located. This constitutes a 4-500 north-south drift in the Anuket border. 

4) Staying with the same Anuket border in 3, above, its border with Neith is similarly southerly in the third map (it starts half way along the Maftet border along the head rim. But in the fifth map, the Neith border has crept north by several hundred metres almost to the beginning of Maftet where that dog-leg in the head rim is. In fact, the parallax of the head rim rebate diminishes the effect. It’s as good as in line with the dog leg. 

There are several smaller contradictions:

1) In the top-right montage, the border of Seth with Babi has been truncated with respect to the older ESA regional map. On that map; Seth used to have a finger protruding 400 metres along the Hapi rim and into the Babi area. This isn’t a contradiction between these recent maps and so might have been an intentional change in the border line.

2) The Seth border is also shown as being too far down Ash in the bottom-left montage frame (difficult to judge with the acute perspective but nevertheless a few hundred metres off because of that acute angle. 

3) In the bottom-left montage frame there’s a green blob on the Serqet rim. This is the smooth area between the pillars of the C. Alexander Gate. It was part of Serqet in the old regional map but this green blob implies that it’s thought to be a part of Anuket peeping round from under the head rim. That’s not possible from this angle- the green blob is definitely the smooth area between the pillars of the C. Alexander Gate. Although this is certainly a contradiction with the old ESA maps, it also appears to contradict the top-left and bottom-right montage frames too, although this area is very nearly over the horizon in both frames. 

4) On the third map, a finger of green depicting Apis extending up into Ash but not there in the bottom-right montage map. This finger is not in any previous map either. 

There are several other anomalies to do with Geb/Bes, Wosret/Maftet and (possibly) Seqet/Ma’at but they are too involved to explain here. 

Hopefully, these contradictions could be corrected, especially the first four. They could lead to future papers inadvertently causing confusion by citing these areas that others interpret as different areas. This would be due to referring to a different map in this presentation (or referring to the old ESA regional map instead).


As Marco has dealt with point 3 in the first list, I’ll deal with the other three of the four as they’re the most important. The second list may have to wait a while but it’s less important. We start with point 1 and then the rest of the first list, i.e. points 2 and 4 will be presented soon in updates. So point 1 will go out right away, on its own, with the updates following over a few days. 


From my comment:

“1) While Bes is clearly marked in the first map it disappears in the second one, taken over by Geb and Anhur. It’s not perspective, you can see the same features coloured differently.”

Here are the two maps. We’ll call the upper one ‘A’ and the lower one ‘B’. They’re not labelled as such in order to keep them close together for toggling. I’ve annotated them with fiduciary points that match morphological features from one to the other. The key follows.


Key (A is upper photo; B is lower photo)

Yellow- 3 dots that are at the ends of three distinctive ridges. The top-left one is on the north-western border of Geb in A but well within Geb in B. The other two are on the Geb-Bes border in A but well within Geb in B where there is no representation of Bes. Geb has therefore taken over Bes in B. However there’s some of Bes that remains in shadow along the bottom in B (i.e. below the brown dots which are described further below).

Orange- a ridge that’s entirely within Bes in A but entirely within Geb in B. 

Light blue- two dots. One is a boulder or protrusion at upper-left in both photos and the other is a boulder or ice patch at lower-right in both photos. The upper left one is within Bes in A and on the Geb Anhur border in B. The lower left one is well within Bes in A but well within Anhur in B. 
Mauve -this sharp turn is correctly positioned at the exact top-right point of the scarp as identified in the related paper but this point is on the Bes-Anhur border in A and on Geb-Anhur in B.

Red- a distinctive feature that’s well within Bes in A but well within Anhur in B. 

Brown- this is top edge of the strange protrusion at the south pole. It sits well within Bes in A but runs along the bottom border of Anhur in B.


From my comment

2) “In the montage [header for this part], right hand column, middle image, “Seth” and “Babi” are actually “Anhur” and “Bes” respectively.”

This is clearly a simple mislabelling but is put here for completeness in covering the first list of four points. I’m sure the paper authors are completely familiar with the Seth and Babi positions. For other readers, Babi and Seth are on the right in the montage image referred to in point 2. Babi is light brown and sitting above the ‘A’ of ‘Aten’. Seth is out of sight beyond it except for a tiny blob of red peeping over the horizon in the distance. That blob seems to show, correctly, the southwestern rim of the Aswan crater at Seth. You can see both regions clearly in the top-left image of the montage. In that image, Anhur and Bes are hidden on the other side of the comet. 

POINT 3 (see update below that complements Marco’s post on this).

3) [covered in Marco Parigi’s post, linked again below but included here for completeness] “On the third map, Anuket is shown including the second heavily shadowed scarp along its border with Atum and even incorporates the third (non shadowed) scarp. These two scarps are incorporated into Sobek in the fifth map. In that map, the border kisses only the first scarp which is the scarp where Vincent et al’s jets 27 and 31 were located. This constitutes a 4-500 north-south drift in the Anuket border.”

POINT 3 UPDATE (8th October 2016).

After completing point four below, it’s now possible to pin down Marco’s Sobek border shunt to a good degree of accuracy. 

Here are a couple of annotated photos, reused from point 4 but with the extended Sobek border shown. The first photo (named update 1) shows the official map with Sobek in light brown and Neith, the subject of point 4, in blue. Both regions extend a long way northward or leftward towards the green of Anuket when compared with the second photo (named update 2). 

The second photo shows a yellow-dotted line tracing what is the line of the more northerly border for Sobek in update 1. The blue line does the same for Neith but is presented in more detail in point 4. 

The two photos are placed together for toggling up and down and have a joint key below. 



Thick beige or light brown line- (above the ‘k’ of ‘Sobek’). This is an arbitrary line past which Sobek extends down into shadow i.e. across where it says “Sobek”. The beige line is covering a yellow line that is on the official map and looks a bit like an actual border of a very small Sobek. That’s a little confusing, especially when drawing in an extension to Sobek. So it’s been drawn over in the same light brown colour as for the Sobek region so as to depict the lower (western) edge of this small illuminated part of Sobek. You can see parts of the old yellow line peeping through but there shouldn’t be any line here that looks like a border. It’s just a place where the top (east) of Sobek gives way to the shadowed bottom of Sobek.  

Medium yellow- (in update 2) this is the line of the Sobek border as it’s shown in update 1. It starts on the right and follows the actual update 2 line for Sobek. That portion of the border is mostly in shadow in update 1 but assumed to follow the same line as update 2 for this short stretch. The most important part of the yellow-dotted line is the section running along the blue line (actually contiguous with it) and then dropping vertically down the neck, past the two big yellow dots and into shadow. The green area enclosed under this line is officially designated as being part of Anuket (green) in update 2 but is deemed as being Sobek (light brown) in update 1. The section in shadow is an informed guess based on the track of the lower (western) Sobek border in update 1. Of course, it doesn’t follow any carefully identified fiduciary points through the shadow as the rest of the yellow and blue lines do so it’s just for general guidance. 

Blue- (in update 2) this is the dotted line that does exactly the same thing for the Neith border as the yellow line does for the Sobek border. It’s presented in detail in point 4, along with a number of extra photos. 

Large yellow- these are the Vincent et al. 2016 outburst locations numbered 27 (upper) and 31 (lower) in that paper. They’re described in detail in part 4 and are used here as fiduciary points for the yellow line to skim past. It skims south of 27 and north of 31. Since the dots themselves are placed on the same fiduciary features in both update 1 and update 2, it’s not just randomly placed dots but actual features that are constraining the yellow line. 31 is admittedly in shadow in update 2 but it’s very close to what for me and Marco are very familiar features. This means the error in its placing on the actual feature in the shadow is no more than half a dot width. The feature is the third point that collapsed en masse without crumbling. It did so over perihelion (probably a little before the actual perihelion date) and is now less visible through not casting a shadow as an overhang. It’s described in point 4. 

Other colours- please see point 4 photos and keys. These features act as fiduciary points to constrain the Neith border shunt. They were carefully identified so the Sobek border shunt uses these as well to get an accurate placing for its yellow dotted line. 

The extent of the northerly shunt of the Sobek border (including the northerly Neith shunt that it wraps around as a finger) is at least 300 metres.


This is added before point 4 because it affects it. It’s a significant movement of the Maftet/Wosret border of 100-150 metres and so it’s really an anomaly in its own right. It’s residing in this list as the fifth point but placed before point 4 due to being related to it. This was the Wosret/Maftet anomaly that was mentioned in the main comment but which was deemed too complicated to explain there. It in fact confused me for articulating point 4 so that explanation isn’t fully accurate. Point 4 still stands but one aspect of it is adjusted as a result of understanding this point, 4A. It’s interesting that despite knowing about 4A, it still tripped me up so it’s certainly going to confuse scientists using or citing this map. 

Photo 4- a close up of the Maftet-Wosret border which is at odds with most renditions of this border, including its position in the photos shown below.

Photo 5- The Maftet-Wosret border from a distance 

Photo 6- A close up of photo 5 with annotations. 

Photo 6 is annotated with the portion of the Maftet-Wosret border that’s visible in photo 4. It’s marked in medium pale orange. This is the true border that isn’t actually marked in photo 4 but its line is nevertheless visible in the frame. The anomalous border in photo 4 is marked in small pale orange dots in a fairly straight line that’s notionally parallel to the true border. It’s some 100 metres or more beyond the true border. 

I’ve also used small pale orange dots for a short curve below the official line. I trace this curve in the lower photos as being the right hand side of that ‘m’ shape plus the curve after it. It would look strange not to annotate the photos below in this manner because this lower curve really does look like part of Maftet in those photos. So this short curve isn’t part of the 4A anomaly which is the longer, straighter section of pale orange above and beyond the official border. 

Photo 7- this is photo 4 again but with the correct Maftet-Wosret border as shown in photo 6.

Photo 8- this is the original used for colouring regions onto photo 7. 

The originals are clearer than the coloured versions so they come in useful for tracing the border lines more accurately. Key follows.

Medium pale orange- the true Maftet border as far as it can be extended (up and right from our viewpoint) along Wosret before going off-frame; and straight up towards the top of the frame, which is along the very defined edge of the head rim before again going off-frame. 

Bright green- two fractures or gouges that are often annotated in this blog as fiduciary points in this area (see Parts 17 and 19). They will also be shown in photos below to ensure we’re anchored in the right place with our various lines. 

Photo 9- same as photo 8 but with the anomalous Maftet-Wosret border in small pale orange. 

Photo 10- this is the Part 17 header, used for extra context from another angle. 
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Red- on the head lobe, this is the head rim. So Maftet and Wosret sit above it and are divided by the medium pale orange line. The red line on the body is relevant to Part 17 and not this post. 

Small orange and bright green- as for other photos above. 

Photo 11- this is one of the photos that will be used in point 4, along with photo 4 as the comparison photo. It shows the same annotations as for the photos above. 

Photo 11 depicts what is in effect a shunting of the Maftet-Wosret border northwards along the head rim. This reduces the degree of the point 4 anomaly, at least with regard to where the Neith border meets the head rim. This shunt is what tripped me up in point 4, below. The Neith border is still nevertheless shunted quite far north when looking further down the neck. 

Photo 12- this is the original for photo 11. Again, it’s clearer. You can see the left hand (northern) Maftet border being traced more accurately along the head rim and the right hand bright green dot has found its home. 


This is a minor correction to the head rim line in photo 4 using its original, photo 8. This caused some extra confusion as explained further down. The two photos are reproduced here together as photos 13 and 14 with new annotations. 


In photo 13, the usual pale orange line shows the Maftet border, including its run along the head rim as in photo 8. In that photo, my pale orange head rim line doesn’t dip in sharply like its coloured-in twin does. Similarly, in photo 13 above, it runs along the true rim and completely ignores the green triangle that’s trying to be part of Anuket. That triangle is dotted yellow and is thereby reclaimed as part of Maftet. That’s because it’s sitting solidly above the sharp head rim line. You can see the head rim line (just) in the much clearer original, photo 14. In that photo, just the apex of the yellow triangle is depicted for orientation. You can imagine the yellow triangle extending to the head rim line. It’s clearly extending across the head with the ‘green’ Anuket neck separated, well away, under the head rim overhang. 

This caused more confusion for explaining point 4 because the only sharp dip in along this portion of the head rim is at the northwest corner of Maftet (just out of frame at the top). That’s the dog-leg referred to in point 4 and most obvious in photo 10. 

Although this anomalous dip looked too small to be that dog-leg, it blends into a ridge that looks uncannily like the frilly ridge just beyond it and off frame (that’s because it’s a delamination from that frilly line and so it’s a translational match). Beyond the off-frame frilly line, there’s a section of Anuket that does indeed seem to encroach on the head rim. So I assumed that this visible section beyond the frilly line was the encroaching part that’s off-frame and that Maftet was now deemed to include this patch. 

If I’d seen the original photo at that time, I would’ve noticed the ‘bright green’ gouge that’s covered by the ‘Wosret’ label and seen it was too close to my supposed dog-leg. But I was hooked by the anomalous sharp turn and knew that it ‘had to be’ the dog-leg because I know there are simply no other dips this sharp in the head rim until the one 800 metres to the north at mid-Serqet (which is the orange match in this blog).


Point 4 had a slight error to do with the dog-leg as explained above in Point 3 but is quoted here from my Rosetta blog comment in full:

“4) Staying with the same Anuket border in 3, above, its border with Neith is similarly southerly in the third map (it starts half way along the Maftet border along the head rim. But in the fifth map, the Neith border has crept north by several hundred metres almost to the beginning of Maftet where that dog-leg in the head rim is. In fact, the parallax of the head rim rebate diminishes the effect. It’s as good as in line with the dog leg.”

Photos 15 and 16- photo 15 corresponds to the third map referred to in the point 4 excerpt above and photo 16 corresponds to the fifth map referred to. The only thing you have to note here is that the northern (left hand) border of Neith shunts itself north in the photo 16 map. It’s therefore dotted blue in photo 15 to show where it ‘should’ be in that map. Neith itself is coloured blue in both photos.


Photos 15 and 16 are reproduced further below with a full key for the other dotted features.

The northern border of Neith is officially marked in both maps. However they are in different places, over 100 metres apart. In photo 15 there’s a blue-dotted line that corresponds to the official line as it’s depicted in photo 16. You can see that the dotted blue line is a long way north of the official photo 15 line next to it. That official line should overlay the blue-dotted line perfectly because the maps should show the regional borders in the same place, following the same features. 

Just for clarity, although Neith remains blue in both maps for photos 15 and 16 there’s a difference in the colours used on the official maps for defining the shunted border in question. The official photo 15 border line is in fact a green line (not blue) that’s bordering the blue of Neith. In photo 16, the north-shunted version of the line is blue (not green) and again, it borders the blue of Neith. That’s why my dotted line is blue. It was chosen for annotating photo 15 so as to show where the blue line of photo 16 should be if it were similarly placed. However, that official blue line in photo 16 (now changed to green in photo 15) is a hundred metres away and notionally parallel to my blue-dotted line. 

References below to “up, down, left and right” are with reference to ‘upright duck’ mode with the head lobe at the top and the body lobe at the bottom. The neck then runs ‘vertically’ between the two lobes. Wosret and Maftet are on the head, Geb is on the body. Anuket is the neck. 

Once the dog-leg issue is resolved, the point at which the Neith line reaches the head rim is roughly the same in both maps. However, the border line in the photo 16 map starts substantially further north at the bottom end of Neith, halfway down the the neck. The anomaly shadows the Sobek northward anomaly outlined by Marco (see his blog post linked in point 3, above). This is because the Neith border going up the neck stems notionally from the northern Sobek border in both versions of the border in the two maps. The fact that the Neith border is essentially an extension of the Sobek border means that the green Anuket area beyond them is a straight vertical sweep up the neck from bottom to top. 

The northward Neith border in photo 16 then bulges out as it progresses up the neck. That’s after we start at at the bottom of Neith, along the top of Sobek, and turn the corner to go up the neck. This bulge is also seen in the more southerly counterpart in photo 15. The bulge makes the two lines roughly parallel for the whole extent of their run up the neck and 100-150 metres apart. 

So the anomaly between the two officially drawn borders in the two maps is a 100-150 metre north-south anomaly. The line in photo 16 is truncated near the top by being obscured by the substantial head rim rebate at this point. We’re looking down at the head and neck somewhat so the rim rebate obscures the top 100 metres or so. If you extrapolate the dotted blue line in photo 15 to the rim, it would touch it just a little way north of the more southerly component. The southerly component does a little left turn at the top before reaching the rim which helps to bring the two lines almost together at the rim. 

Here are some more photos to nail down the exact path of the more northerly version of the two lines. I may do the more southerly one in due course but the northerly one is easier to trace. That’s because it was overlaid on a more detailed, hi res photo in the first place. 

Photo 17- this is photo 15 reproduced. It also includes the version without the blue-dotted line for toggling and comparing (but see photo 18 for a more detailed blue line). Originals or very similar versions for toggling aren’t designated separate photo numbers. 


Photo 18- the exact line in smaller blue dots. It’s laid on the original version of the photo used for the map. Includes non-dotted version for toggling and a more zoomed-out version for context, showing more head rim etc.


Photo 19- this is the same as photo 16 and its key for all the other colours follows. 


(this key includes fiduciary points and lines that are shown in later photos from a different viewpoint so as to show we’re tracing the correct blue-dotted line in photo 15). 

Pale orange- the Maftet border (medium pale orange) and the anomalous Maftet border (small pale orange). This was outlined in points 4A and 4B. 

Light blue- two fiduciary boulders (both near the red line).

Red- a distinctive ridge. 

Green- various curved and winding ridges that enclose dips. The green curve that straddles the border of Neith is an important fiduciary point for getting the line right in later photos. The two ends of the curve extend all the way down to the second and third ridges that are arrowed by the OSIRIS team in the original below. This means these two ridges are joined in a curve at their top ends. Only the curved end is relevant here. There’s also an isolated green line next to the yellow dots and not very visible so it’s dotted with bigger dots. This corresponds to the first or left hand ridge, arrowed in the original. This is a later photo than photo 15 and its annotated relatives below. The obvious protruding, overhanging points on the earlier photos have collapsed in this version (see ‘yellow’ below). 

Yellow- these two dots denote the Vincent et al. 2016 outburst sources numbered 27 (upper yellow) and 31 (lower yellow). 27 sits on the site of the most easterly collapsed point that was identified by Marco Parigi (see link below). 31 sits at the tip of the collapsed point that I identified. Both points used to be pointed overhangs. These collapse identifications were made before the Vincent et al. 2016 paper was published. Marco’s point collapsed fully into a pile of rubble. My point collapsed en masse, retains its original form and is almost completely camouflaged, being flat on the terrain it once overhung. These two collapses makes the ridge appear both shorter and ‘blunter’ in the sense of losing its three points. Marco identified the middle point’s collapse too but that’s a smaller collapse and Vincent et al. don’t show an outburst location for that. These three collapses makes comparison of this ridge in pre- and post-perihelion photos very challenging. The reason for explaining this here is that Marco and I are intimately aware of the morphology changes in this area. It follows that any apparent misidentification of this ridge in the lower photos isn’t in fact a misidentification. It’s the same ridge. There are pointed overhangs for this ridge in those other photos below and no pointed overhangs in this photo. Once we’re aware of this, it furnishes us with a very useful fiduciary point to check on and constrain the other two green lines. 

Photo 20- this is the original used for the photo 19 map. Both are zoomed-in versions of the true original further down, at the bottom of point 4.

All colours are the same as for photo 19. 

Unannotated versions for photos 19 and 20 (not numbered). 


Photos 21 and 22- photo 21 is the same as photo 18 but with the same annotations as photo 19. Photo 22 is photo 19 reproduced for toggling between the two so as to check all the fiduciary points match. 


Photos 23 and 24- this is the same set-up as for 21/22, above but 22 is replaced by its original with the even clearer annotations for toggling and checking the fiduciary points match. 


Photos 25 to 28- the zoomed-out originals used for point 4.



This post completes the presentation of the more important anomalies in the recent OSIRIS map updates. These were presented as points 1 to 4 in my pasted Rosetta blog comment near the top of this post. They were dealt with in detail and in sequence in this post but with two extra points numbered 4A and 4B sitting between 3 and 4. This was because 4A and 4B were pertinent to 4 and needed presenting before point 4 for that reason. However, they were anomalies in their own right. They therefore augment the list of the more important anomalies from four to six. 

The second list (of four less important anomalies) was also in the Rosetta blog comment. This list will get the same treatment in due course but will be left for now owing to a large backlog of stretch theory posts. It will be in a separate, twinned post because this one is now rather long. It will be linked below this conclusion. So if there’s no link, it hasn’t been done yet. 

If, however, anyone including OSIRIS scientists, independent scientists or citizen scientists would like the other list dealt with earlier, please leave a comment below or tweet/DM me: @scute1133. I shall then do it sooner rather than later. 


Marco Parigi’s blog post on the collapsing points along the first ridge:


 Link to my comment:

Link to Marco Parigi’s comment which was below mine in the same comment thread: