67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 33

THE MONOLITHIC SLIDE THAT OPENED UP THE CRATER AND COVE  

 

Red arrow- direction of slide. The tip of the arrow is touching the back rim of the small crater that sits under the head cove. The cove used to sit on this crater. Although some upper portions of the crater side rims also moved backwards, only the back rim slid in its entirety from rim tip to crater floor. In subsequent photos it looks more like a crater, or rather, a horseshoe remnant of a crater than it does here. In this photo, the nearside rim appears to merge with the floor. The tips of the red V kiss the ends of the horseshoe. The back rim is about 80-100 metres high from crater floor to rim tip.

Blue dot- the north pole.

Terracotta and yellow- the shear line where the head lobe sheared from the body. The yellow portion is the section of the shear line where the cove on the head lobe above fits to the body. The visible part of the head rim shear line is also shown on the head at the left of the photo. The small, yellow section fits to the near end of the yellow section on the body because it’s part of the cove. However, it’s not the true match- it’s a thin layer that’s delaminated upwards from the true match which is hidden below it. That’s why it doesn’t follow the ‘gull wing’ shape on the body. The hidden, true match follows the gull wing faithfully (see Part 5 and below). The terracotta portion peters out beyond the yellow portion due to body matches being lost on missing slab A. 

Photo 2- ESA regions map for orientation in this post. 

 

INTRODUCTION

This part could be considered as describing a mirror image of the three sink holes sliding back in Part 32, except this slide actually opened up a single hole rather than delaminating an existing one into three. Today it isn’t a hole but a horseshoe crater. It was a full hole or crater when the head lobe was seated on the body across the end of the horseshoe. This slide is a mirror image of the three sink holes because the two slides occurred at opposite rim tips of the Site A crater. 

Part 34 will rely heavily on this part and some evidence for this part will be presented in Part 34, such as the ‘gull wing’ slide.

All references to up, down, left and right are from the ‘upright duck’ viewpoint unless specifically stated. The upright duck viewpoint is with the head lobe of the duck shape positioned directly above the body lobe. 

BACKGROUND

In Part 32 we looked at the three sink holes, showing that the two smaller ones had delaminated from the large one by sliding back across Site A. Site A is the crater left by missing slab A and is called that because it was one of the candidate sites for the Philae lander. The tell-tale sign for the sink hole slide-back wasn’t only seen in the slid, terrace-like layers in the immediate surroundings of the three sink holes but also a long way down Ash, where layers had ridden up just like on the head lobe (Part 29). Perhaps we should say they are ridden-down layers because they slid down the body. That means it was in the opposite direction to the riding up on the head lobe and one would expect that to be the case seeing as Ash is on the opposite side of the shear line.

It was shown in Part 32 that the tensile forces across Site A and the slab A extension were radial in nature. That means the sliding and riding down of layers was radial too. The force vectors were centred on a point which was close to the large sink hole and also near the north pole of rotation. This strongly implicates stretch by centrifugal spin-up as being the cause of those forces. If that’s the case, the logical thing to do would be to carry on tracking round west towards and across Babi. We could then see if the same radial pattern is apparent. If it is, it would have to be fanning out in the required direction, away from the north pole or a point fairly close to it. 

We had already seen in Part 32 that there was a flaccid-looking ridden down layer in Ash that matches to the Site A crater rim. There are mini matches for this layer but we’ll leave those to another time. The average tensile force vector (stretch vector) of this ridden down layer was away from a point just to the right of the current north pole, complementing the other radial vectors.

The left hand side of the Site A crater rim is quite straight and points along a line that runs just to the left of the pole. It’s probably straight because it stretched backwards towards Ash along that line. It did so in sympathy with the flaccid, ridden down layer behind it. And one would expect this behaviour anyway because the three sink holes on the opposite rim delaminated and slid back in the same manner.

So the yanking back of this left hand side of the Site A rim was itself directed away from the current north pole, which is promising for our radial stretch vector studies. At the tip of the left hand Site A rim, there’s a small crater that fits to the so-called cove on the head lobe above it (matched in Part 3). And now it appears the small crater itself is more affiliated to the Site A rim than previously thought. This involves its relationship with rock C. Regular readers will know all about the rock C seating at the back of the small crater:

Photo 3- the header photo from Part 15, rock C. 

 

Rock C is sitting upside-down in relation to its seating. It flipped over when it drifted across Site A. This is covered in detail in Part 15.

The apparently solid block of the rock C seating used to take up the volume of the small crater before sliding back. You can see the crater just below the rock C seating in the photo. The seating (the two closer yellow dots) is kissing the rim of the crater so rock C was kissing the rim when it was seated there. 

The seating should, for our purposes, include that square that the lower left yellow dot is touching. That’s because the rock C perimeter went round the back of it and so the rock was the size of that entire isosceles triangle you can see but minus the square. The lower left yellow dot is where the front edge of rock C ended against the crater rim so its position is technically correct but a tad misleading in terms of depicting the true width of the rock. Once you get past the square, the width is the same as the back rim of the crater. It’s best to visualise rock C as that entire isosceles triangle with a square gouge at its thick end. That gouge will be seen to be quite important.

The combination of rock C, and its seating used to take up the volume of the crater. So rock C and the crater rim it kisses used to be slid right forward to that straight, front lip of today’s crater, filling the horseshoe shape completely. The front lip marks the drop-away to Hapi and is where the shear line runs. When rock C, plus seating, slid back towards Ash (away from the current north pole) they automatically created the small crater as we see it today. The sides of today’s crater remained in place while just the back rim slid back. Rock C was really just part of the rim at that time so it slid back as well. 

We shall see in the next part (34) that the gull wings were originally attached to the left rim of the small crater. The gull wings were first mentioned in Part 5. They detached at the same time that rock C and its seating slid back. They recoiled to the left (looking from the upright duck viewpoint) along a line that’s also radial from the current north pole, creating the upper level crater as they did so. That’s the wider, shallower crater that surrounds the left side of the small crater. That gull wing slide dragged the cove (Part 3) out to the same spot because the cove was still attached to the body at that time. 

This means the gull wings we see today on the body must have originally fitted to rock C. That would be when rock C was sitting on its seating and forming the topmost part of the filled crater volume- and when the gull wings were clamped to the side of the crater. That in turn means that today’s rock C, displaced 300 metres away on Site A, should be an upside-down gull wing shape:

Photo 4- Rock C. 

 
photo 5- the gull wings. 
 

Photo 4 depicts the gull wing shape on rock C in dark green. 

Photo 5 is the head-body match of the gull wings from Part 5. Multiple colours map across the various individual mini matches. Full zoom is recommended.

That dark green perimeter of rock C would have attached to the gull wings. Since rock C is flipped over in relation to its seating, it needs to be flipped back again to make the match. That would flip the upside-down gull wings in the photo to an upright position and facing away from us, which is the correct orientation for the match. At the time of posting Part 15 it wasn’t known that rock C and its seating had slid back with the Site A rim to open up the small crater. Nor was it known that gull wings were clamped to the left side of the small crater. So rock C wasn’t perceived as being an upside-down gull wing. 

One additional point. The sides of the small crater have strong-looking, straight ridges that run vertically, like walls, to the bottom of the crater or horseshoe shape. It seems that these were strong enough to resist the tensile forces of spin-up. But it appears they acted as perfect side walls for the rock C and seating combination to slide along and between. In photo 3, the upper right yellow dot under the ‘e’ in ‘here’ is at the crater rim, abutting one side wall. Lower down, this wall’s vertical face is in shadow. The other side wall is abutting that small square we discussed above and has a dark shadowed side facing towards us as well. That’s the ‘hollow block wall’ that fits to the cove above in Part 18. That’s very straight, looking from above. In upright duck mode, the hollow block wall is on the right of the crater or horseshoe and the other side wall is on the left. 

THE PALEO POLE 

The paleo north pole may still have been slightly below the small crater (towards Ash) at the time of the rock C seating slide, thereby complicating the issue. That’s because it had to be lower down the body than the current north pole when the head lobe was seated on the body lobe. That would be in keeping with the lowered centre of gravity. Subsequent events show that the head was seated during the slide and these events will be laid out in an upcoming post. If the pole was indeed lower than the small crater, the rock C/seating slide should theoretically be the opposite way. However, if the Site A rim acted as one solid chunk as it seems to have done, then rock C and its seating on the ‘wrong’ side of the pole would have been dragged back by the vast amount of mass on the ‘correct’ side of the pole. It would just mean that the shear line opened up very close to the paleo pole but chose to shear at the nearest available weak point. That weak point happened to be a little beyond the pole. Also, the radial force vectors near the pole itself are very weak due to the short radius of rotation. The apparently strong radial force signatures right next to the pole we’ll see in the next post are probably more to do with the bigger masses at bigger radii tugging on crust material at the pole. 

Alternatively, the whole crust in this vicinity might simply have continued to slide south just after the head lobe sheared and was rising apace. The paleo pole would be creeping up fast from its lower position to its upper position while the comet was slowing from a ~2-hour rotation to a ~5-hour rotation. There was still a fair bit of ‘centrifugal’ force on the site A and Ash area during this period even if it was only strong enough to induce a continuation of southward sliding of already loosened crust. It didn’t have to be anything like the centrifugal forces needed for ejection to orbit or escape. And we know from Part 32 that Ash was dragging elements of Site A with it a long way down the side of the comet. 

A NEW ROCK C MATCH TO THE CRATER RIM

Another rock C match that wasn’t presented in Part 15 is the two mini-scallops at the thick end of the rock. They’re dubbed ‘mini-scallops’ because we’ll be referring to the larger scallops in the head cove in the next part and need to differentiate between the two types.

The rock C mini-scallops are presented below in photos 6 and 7 because we’re in the process of showing all the available evidence for rock C kissing the small crater edge. Having done that, we are showing that the seated rock C and the back of the crater it matched to both slid back as one mass of ‘rock’, thus opening up the small crater. Before we look at the photos, here’s the reasoning as to why rock C might have these mini-scallops running up its thick end. 

It would have been quite a spectacular ‘open sesame’ style slide: those well-defined crater side walls stayed in place, like rails, and only the back portion, including rock C, slid back along the flat floor of the crater. Rock C and its seating simply represented the tip of the Site A rim, sliding back in its entirety. The slide was towards Ash just like the three delaminated sink holes on the opposite side of the Site A rim. The slide would have caused that very straight tear across the front rim of the small crater. But at that time, the head lobe would have been pressed against that straight edge with gases spewing up through the fissure between crater and head. Indeed, the head formed that side of the crater at that time. The straight crater rim is the shear line where the head lobe sheared from the body. It’s of course likely that a developing fissure would be responsible for weakening the rock C/seating combination and working it loose from the head lobe. That would allow it to detach and slide back under the influence of centrifugal forces. 

The shear line runs away from both ends of that crater rim and on, in opposite directions right round the comet. They meet up again at the south pole in a similar scalloped area of apparently violent outgassing (Part 30).

This means that the rock C/seating monolith tore from the head lobe at the front rim of the small crater and this was therefore a premature unzipping of the shear line before the sections either side of the crater unzipped. It also means that the rock C mini-scallops were right on the shear line. That explains why there was so much outgassing scouring up past rock C. It was one of the the most prone areas on the comet for catastrophic outgassing. And the reason this section failed before the rest of the shear line either side is due to the radial nature of the tensile force vectors. The spin-up of the comet was causing the crust to start sliding away from the pole under the influence of centrifugal force. And at the pole itself, the forces were all pulling radially around one point- the small crater. 

Photos 6 and 7, rock C mini-scallops and their matches around the back of the small crater. Remember, you have to flip rock C over in your mind’s eye so the gull wings turn to face away from you and the two mini-scallops are sitting further away from you with their gas ejection arrows pointing up, not down. More explanation below.  

   

The crater photo shows the same mini-scallop annotations as the rock C photo but projected into ‘thin air’ above its seating. In other words, they’re following the lines of the mini-scallops as if rock C was sitting there (flipped right-side-up) in its former home. You can see the two (physically present) mini-scallops at the back of the small crater that feed seamlessly into the two mini-scallops of rock C above them.

The red line on rock C, photo 6, follows the top perimeter of the 90° gouge that runs down the side of the rock. That gouge was briefly mentioned, above. The gouge itself is running down the other side of the rock, out of sight, in photo 6. The top perimeter is almost out of sight as well but nevertheless visible in high profile. The corresponding red lines on the seating aren’t in thin air like the blue lines. This is because if they are at the far, top side of the rock in photo 6, they must be at the near, bottom side in photo 7. That means they’re a conventional mirrored match, kissing each other. The match forms the base of a square chimney-shaped void that runs up the side of rock C (the gouge). That void, though out of sight in photo 6, is discussed, with photos, in Part 15. The chimney is a vertically sliced diagonal half of a chimney in the gouged rock but the square it fits to (in photo 7) suggests there was mass to the left, in that view, that completed the other two walls of the chimney. Further evidence of this is that the square base of the supposed chimney has two lines running down the back rim of the small crater from it. These appear to be related to the chimney because they’re the same width and parallel. So, just like the blue-dotted mini-scallops, the chimney had its own flattened conduit up the back of the small crater rim. The conduit would have been active when rock C was slid forward into the crater volume and pressed against the head lobe at the shear line. 

That completes the matching of rock C to the back rim of the crater. The matches for its perimeter seating above the rim are dealt with in Part 15. 

Although we can’t be sure yet, it does look as if there was a chimney with mass to one side and along the crater rim completing the third and fourth sides. If the rim was pressed against the head lobe when in the crater, that would create one more side. And the side of the cove on the head may well have formed the fourth side. We’ll see below that mini-scallops on the cove might have fitted to the gouged side of rock C when it was at the back of the crater. Even if the cove wasn’t sufficiently overlapped to do that, it still kissed the corner of the chimney base so we are discussing exquisitely small adjustments here. 

All the matching rocks and scallops and flattened conduits would originally have been right on the shear line at the sharp, straight lip of the small crater. They would have had the head lobe pressed against them causing the conduits to be flat, lower down, and scalloped, up high near the exit (i.e. fluted due to explosive gas escape with the sudden pressure drop). The two light blue-dotted scallops, and the red chimney which is a scallop of a sort, start at the base of rock C and that’s presumably why rock C became loosened at that point. 

Since the original gull wings from Part 5 will be seen to match to the side of the small crater (Part 34) then the rock C gull wings had to be inside the crater we see today in order to match to them. In other words, the dark green gull wing line depicted on rock C, above, had to kiss the small crater edge as well. That means rock C had to be sitting right in the crater when the gull wings were attached i.e. filling up the crater volume completely (along with its seating). 

The seated base of rock C represented the point at which the pressure drop caused a last burst of extra explosive gas and slurry escape (circa 40-50 metres depth). That caused the fluting within the rock C mini-scallops- they were scoured out. Eventually, after much outgassing and loosening, rock C and its seating slid back towards Ash and away from the shear line, thus opening the small crater. 

THE ROCK C MINI-SCALLOPS CONTINUED ROUND THE CRATER FROM THE HEAD COVE MINI-SCALLOPS. 

The edge point of the chimney was matched to the cove tip, 1 kilometre above it in Part 3 with red dots. Now we can join (not match) the actual mini-scallops of the cove to the mini-scallops of rock C. The scallops that run round the perimeter of the cove continued across the end of rock C when they were both clamped side by side and formed the top perimeter of the small crater rim.

Photos 8 and 9, below, show the cove mini-scallops and the rock C mini-scallops. They are the same photo. The first is a skeletal annotation showing the cove mini-scallops and rock C crater rim features. The second inserts context around them. 

As mentioned above, any overlapped match of the cove tip mini-scallop to align with the chimney is somewhat tentative. The main point here is that the cove tip did seat to the crater rim next to rock C and both cove and rock exhibit the same characteristic mini-scallops. These would have been running vertically up the crater side, both up the cove (which would have formed one side of the crater) and up the back side of the crater, including rock C when seated. Just to be clear, we’re not matching the cove mini-scallops to the rock C mini-scallops in the sense of marrying them in a conventional mirrored match. We’re simply showing that the rock C mini-scallops continue on round the crater rim from the cove mini-scallops when the cove was seated. And that they were similar in character. The full key is below. 

Photos 8 and 9- the rock C mini-scallops continued on round from the cove mini-scallops and are similar in character. (See also photo 6 for rock C close up). 

   

Light blue (full zoom needed)- on the left end of the head lobe cove, this depicts four ribs delineating three mini-scallops. On the body, it’s just two very small light blue dots marking the centres of the rock C feeder mini-scallops. They are not the ‘thin air’ matches. They’re physically there in the crater rim side and directly below the rock C ‘thin air’ matches. They’re the two ‘feeder’ mini-scallops for rock C. They’re more obvious in photo 7.

Terracotta and yellow- these mark the shear line and cove. As with the header photo, the yellow line is simply the section of the shear line that matches the cove on the head to the crater and gull wings on the body.

Red- on the body, this is the base of the hypothesised chimney that is thought to have had a square cross section. Only two sides of the base are marked because those are the perimeter of rock C and therefore depict the gouge that runs up the side of rock C. The gouge represents half the chimney, sliced diagonally down the middle. The other half would be made complete if we could find the other two sides or chimney walls that would sit on the two undotted sides of the square base. One wall would be the head lobe when rock C was shunted against it. The other may be that thin scallop at the very tip of the head cove. That might seem rather tentative but that cove tip has always been matched to the front corner of the square chimney base. If we shunt the match one chimney width away from us (in this photo) towards Ash, then that thin scallop on the tip of the cove becomes the missing side of the chimney. And of course, it’s the correct width. So that scallop is dotted red as well, along its base, in recognition of this possible chimney match. 

Orange- rock C seating perimeter and approximate position of the present-day rock C. The seating perimeter includes the red, 90° gouge of the supposed chimney. The tip of the rock C seating is sharply bent up. On the actual rock it’s bent down because the rock flipped over.

ROCK C LOOSENING SCENARIO

The fact that the pressure drop and explosive scouring of the the rock C mini-scallops started at the base of rock C probably isn’t a coincidence. That demarcation line may have been the very reason rock C was detached at that particular depth. The base of the scouring betrays the threshold of the explosive pressure drop. The base of the explosive pressure drop is where the rising gases and slurry might find their way in between fracture planes with less mass and therefore weight above them than lower down. That would explain all the flat-bottomed square trays in the rock C seating. They have pooled slurry in them. 

Photo 10- the flat, square trays in the rock C seating. 

 

Slurry was mentioned above because there are signs of slurry deposits all round this small area of violent tearing and sliding (Parts 7 and 8). In addition, the small crater has a mirror-flat floor, perpendicular to the gravity vector. It may have a thin coating of dust but it’s almost certainly the hardened slurry underneath that caused the flatness. It’s just like pouring thick oil paint into a tray and seeing it find its own level. The upper tier crater extension running across to the gull wings is almost mirror-flat too. 

AN ADDITIONAL MATCH TO PROVE THE ROCK C SLIDE

Since we now know that the three sink holes on the other side of Site A delaminated with a multiple slide-back of terraced layers, it would be reasonable to look for signs of the same behaviour on the rock C side. That means looking for delaminated, slid-back layers behind the rock C seating and towards Ash. If they could be matched to their former seating, all the better. 

In Part 14, rocks A and B, currently out on site A, were matched to a seating location on the crater rim that is contiguous with the rock C seating. That rock A,B seating has an identical shape just behind it, towards Ash, in the same direction as the rock C/seating slide. So that shape was originally part of the rock A,B formation and slid off the top of rocks A and B at the same time that rock C and its seating slid back to form the crater. The distance of the rock A,B match slide is the same distance as the rock C/seating slide.

Photo 11- the rock A,B match slide. This is a screenshot of the Part 14 post, rather than just the photo on its own. That’s because it contains the first line of the key showing a naive recognition of the match without realising it had slid back.  

 

Terracotta- the shear line. 

Pale blue- rocks A and B out on Site A to the right, and their seating to the left. 

Dark blue- the rotation plane corridor along which they drifted from their seating. 

Pale green- (not simply a similar shape!) the rock A,B match that slid back from its original position. The slide was a delamination event just like the multiple delaminations that caused the numerous terraced layers around the three sink holes. This rock A,B match was originally seated directly on top of rocks A and B. Since it’s a single delamination identification and the three sink holes sport multiple delaminations, it would be reasonable to suppose that all it’s surroundings have also delaminated from a position nearer the shear line. That suggests there are multiple delamination matches yet to be identified around this match.

PHOTO CREDITS:

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

To view a copy of this licence please visit:

http://creativecommons.org/licenses/by-sa/3.0/igo/

All dotted annotations by Scute1133.

67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 32

THE LARGE SINK HOLE DELAMINATED INTO THE THREE SINK HOLES WE SEE TODAY.  

ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA/SGS/PSA&ESDC/Scute1133

Photo 2- the ESA comet regions map to help with locating the regions referred to below. 

 
BACKGROUND

Part 31 presented the lattice of stretch vectors in the so-called slab A extension and the red triangle. The stretching of 67P was due to the ‘centrifugal’ force brought about by the comet spinning up to somewhere around a two- to 3-hour rotation period. The spin-up would have occurred via asymmetrical outgassing. Alternatively a close pass at Jupiter some way under the 220,000 km Roche limit would supply the stretching force via differential g accelerations instead of spin-up. 

Part 31 stated, “there are other areas nearby that show similar stretch vector signatures that are orientated at a slightly different angle from this lattice.”

If we trek across Ash from the red triangle and round the perimeter of the slab A extension, we cross through the lattice and end up in an area behind the three sink holes. Here, we find an area with lines that resemble the lattice but they are fainter, broken and further apart. Also, their aggregate direction seems to be at a slightly different angle from the lattice orientation around the red triangle. It all looks a bit woolly. 

Photo 3- the smudged lattice lines in Ash (larger dots). 

 
But let’s look at those lines in detail.

Photo 4 – the Ash matches behind the three sink holes. Includes unannotated version.

   

Photos 4 and 6 have narrative keys so the end of the key is denoted by the symbol ‘/////’. 

Fuchsia- the fuchsia circle is the large sink hole at one end of the flat area of Site A. The two horseshoe arcs below it depict the other two sink holes set in line behind it and towards the back of Site A. They are smaller, shallower and joined to the main one. The three together form a trench with bulbous sides. 

Long terracotta line- the shear line for orientation purposes. The terracotta L-shapes in Ash are stretch matches (see below). 

Yellow next to shear line- the beginning of the Site A ‘crater’ perimeter. The rest is left out so as not to clutter the photo. 

Orange- missing slab B (Babi-Part 9).

Bright green- on the right running away from the shear line- this is the right hand perimeter of the slab A extension. It’s contiguous with one long side of the red triangle. Bright green is also used for the triad of matching bright green dots (see below) because when nested they sit almost at the opposite end of the slab A extension.

All other coloured dots, which are all below Site A and sitting in the Ash region, depict specific features that are repeated on the three recoiled layers. 

Red arrows- these depict the directions in which the matches flare out across Ash and therefore betray the the direction of the stretching forces acting on them. 

/////

We can see the matches flaring out wider as they extend down Ash, away from the Site A crater rim and sink holes. If we replay the stretch movie backwards, the bottom layer of matches moves up Ash, contracting slightly along its length (horizontally in this view) as it does so. It scoops up the second line as it passes it and then the two nested lines move further up Ash. Again, they contract across their length as they approach the third line of matches and nest with them. This time, the horizontal contraction is more marked and means that the red, blue and dark green matches get lost in the squeeze, leaving just the outside two to join together: the terracotta L-shape and the bright green triad. The focus of the contraction is the third sink hole which is the second one from the main, large sink hole. This means that:

1) The stretch vector lattice does extend further across Ash and all the way to site A. 

2) The whole of Ash is one giant recoil area. That at last explains why the back rim of Site A continues on in a perfect arc along the back rim of the slab A extension- all the way to the red triangle (see photo 5, below). Both areas were subjected to the same stretching and recoil event. Ash is simply an onion layer that slid back under the influence of the stretch vector after decoupling from its counterpart a long way further up the body and somewhere on site A (and the slab A extension). That beautifully smooth arc betrays the subtly changing orientation of the stretch vectors across Site A, the slab A extension and Ash. This may be the reason that Ash looks a bit like a crumpled blanket. It didn’t lose material and in fact consists of excess, flaccid folds as a result of material that slid back. For regular readers who can stitch together all the references to the Slab A extension morphology since Part 22, this has now almost fully explained its morphology: the scalped skin split in two. Half is plastered against Anuket and the other half recoiled back to this curved line and is now part of Ash. The tear was about midway across. It was acknowledged as not being fully understood back in Part 22 and said to be a work in progress. It was stated that it must have been subjected to the same process as site A but what that process was remained a mystery. The answer is recoil and in retrospect, it looks rather obvious. All those references regarding the demise of the slab A extension will be collated into one post fairly soon, along with some extra evidence.

3) The three sink holes are orientated in line with the average direction of these newly discovered stretch vectors that flare out down Ash. Since all the matches converge on the third sink hole, it means that this sink hole and the second one behind it had to have at least been under tension along this vector. Since the vector is in line with the alignment of the holes, it’s reasonable to suggest that the holes delaminated along that line, from one big hole into three holes. Indeed, all delaminated strata either side of the sink holes is delaminated in this same stretch direction (see photo 6, lower down).

4) The stretch vector change betrayed by the Ash recoil curve is radial, meaning the vectors are focussed (nearly) on one point, right next to the north pole. That’s a huge clue for stretching via the centrifugal force of spin-up.

Photo 5- the Ash recoil showing the neat curve where the Ash onion layer recoiled to. 

   

Yellow- portion of Site A (the missing slab A crater) up to where its back rim merges with the slab A extension back rim. 

Bright green- the slab A extension back rim that continues on from where it merges with the Site A back rim. 

Photo 6- the delaminated layers next to the three sink holes. 

   

ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA/SGS/PSA&ESDC/Scute1133

Fuchsia- the three sink holes. The main one is nearest to us and the delaminated ones are shown as horseshoe arcs beyond it. Looking at the floor level of the second hole, it’s on the same level as the large, flat expanse of Site A to the right as well as the smaller expanse to the left (at the bottom of the dotted terraces). This is a strong clue that the side walls of the main sink hole slid back along this fracture plane thus revealing the floor of the second sink hole which was previously sitting under the slid-back strata. It is therefore not a sink hole at all but the sliced top of the main sink hole, sitting on a newly exposed flat expanse. The same process would apply to the third sink hole, the only difference being that the revealed floor of that hole was another stratum or sub stratum further up from the second hole. Despite not being sink holes, after all, we’ll continue to call all three “sink holes” for the time being because they are called that by everyone who is interested in 67P. Even the main hole will eventually be shown not to be a sink hole- at least not in any conventional definition of the term whereby a cavity slowly forms and the roof collapses. 

Red arrows- the upper pair show the direction of travel of the fanning-out matches, thus betraying the stretch vector that pulled them along those two  paths. They point upwards because we’re looking from the opposite direction to photo 4 where they were pointing downwards. The single, lower arrow is pointing at the large sink hole. More importantly, it’s pointing in the direction along which the line of three sink holes is arranged. And this direction is in the average direction of the other two arrows. Hence the three sink holes were under a tensile stress force in this direction while everything around them was actually moving back down the comet under that same tensile force (proven by the matches). It’s therefore reasonable to suggest that the holes were also delaminating in that direction. 

Bright green, blue, dark green and terracotta- these are the same features as in photo 4 but viewed from the exact opposite direction and from lower down. So they are converging towards us in a foreshortened perspective. The yellow and red dots are left out because they’re whited out here. Also the ‘lower’ dark green dip in the other photo is invisible here. The ‘lowest’ terracotta feature (highest here) is almost unrecognisable due to foreshortening so it’s left unannotated for fear of obliterating it. It continues beyond the second terracotta match in a zig zag. 

Light orange- this and the first terracotta L-shape match that touches it were depicted as one terracotta L-shape in photo 4. That’s because it was fuzzier and in shadow in that photo. Here, it’s divided into the initial seating area, which is the pale orange dots, and the first terracotta match that slid back from it. You can see that the first terracotta match is a right angle with a thick finger of material. If you reverse the stretch movie, the finger slides towards us and clicks into place over the finger depicted by the pale orange dots. Its right angled part then clicks into place by curving round the back of the third hole but it may have just gone straight across the back of the bright green dots. 

Pale green- strata that delaminated in the same direction as the average tensile force (stretch) vector. That would be the same direction as the delaminating holes. There are terraces of multiple matches fanning out on either side of the holes. 

/////

Photo 6 basically shows everything in the vicinity of the sink holes getting yanked back, away from our viewpoint towards and across Ash. All this material would have originally been nested together with the three holes themselves also nested together. 

THE LARGE, ISOLATED CRATER IN ASH MAY BE RELATED TO THE SINK HOLE  

 
Photo 7- the crater in Ash. It has a light blue dot in its centre. Its twin in the ‘flared matches’ second tier is beyond it, also dotted light blue. Photo 4 also gives a good view of it. In that photo it’s got the dark blue matches either side.

There’s a match in photo 4 that wasn’t annotated. It would have cluttered up the image too much. That strangely isolated crater in the middle of Ash is sitting right in the middle of the matches. It’s the only large, circular crater on the comet with a completely intact rim. It’s also absolutely constrained to rise up Ash with the matches around it. And when we look at photo 4 again we can see that there’s a big circle right above it, in the correct direction of movement. It’s not just sited anywhere further up and in the right direction but it’s shadowing its L-shaped terracotta match on the other side of the flared set. In other words, the layer it delaminated from is the same as the the one from which its partner L-shape delaminated from before they both slid and flared another level down. The same principle should work with the next layer up. The L-shape has already been matched to the side of the third sink hole. If the crater behaved as it seems it did, sliding with the L-shape from the second to the third level, then it must surely have slid with the L-shape from the first to the second level. That means it was crammed right against the L-shape at ‘level 1’ and that in turn suggests it was sitting right on top of the third sink hole (presumably when it was an incipient sink hole). It would seem remarkable for a crater to move that far and stay intact. But the matches already constrain it to move from its circular, level 2 twin to its current position so if it had to move from there it’s not so implausible for it to have moved the whole way. And since we are saying that the three sink holes delaminated and that crater in Ash has now been traced to the third hole, it’s just as conceivable that it originally sat over the main sink hole before it delaminated into three. 

As a check, one can look at the unannotated version of photo 5. If you concentrate on that smooth curve forming the back rim of the slab A extension, that betrays the stretch vector or tensile force vector because that’s the curve along which it found its equilibrium after springing back. The tensile stretch force would be at 90° to the curve. If you draw a line between the crater and the main sink hole, whether it’s straight or via its slightly kinked matched path, it crosses the curve at 90°. If you replayed the stretch movie in reverse, the crater would always be headed for the large sink hole.

PHOTO CREDITS FOR NAVCAM PHOTOS:

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

To view a copy of this licence please visit:

http://creativecommons.org/licenses/by-sa/3.0/igo/

All dotted annotations by Scute1133.

PHOTO CREDITS FOR OSIRIS PHOTOS:

-Original image provided as .IMG file in the archive delivery from : ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

-Original image processed by ESA/Rosetta/SGS/PSA&ESDC to create image for Archive Image Browser

All dotted annotations by scute1133.

67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 31

THE LATTICE OF STRETCH LINES ON 67P   
 
For those readers who are familiar with the so-called red triangle, here’s another version showing which lines in the above lattice correspond to the red triangle. It also includes the four coloured body matches/anchors that match to the head rim (Part 24). 

 
Here’s the shape model with the same lines annotated as well as the paleo rotation plane: 

 
Red- lattice.

Brown- Paleo rotation plane (Part 26).

Yellow- missing Anubis slab (Part 23). The lattice would presumably have spread symmetrically across the missing surface to the right.

Green- the silhouette of Apis on the horizon is the straight line just above the green line. Apis is bisected by the paleo rotation plane. It straddled the paleo plane because it constituted the flattened tip of the symmetrically stretched diamond shape.

There are possibly several additional lines crossing the red lines we see above, which would make it a more defined  diamond lattice. These lines are less obvious and are left out of the header annotation so that just the most obvious ones are shown. They are easier to see in the shape model version but are still left out. 

If you can visualise the diamond lattice with the additional lines, you can see that each individual diamond cell is longer in one dimension i.e. across one diagonal. Those long diagonals are all aligned parallel to the paleo rotation plane as you’d expect if the comet had stretched along the paleo plane line. Each mini diamond has roughly the same stretch proportions as the stretched body lobe diamond, which is interesting. That wouldn’t be something that’s easy to predict but it makes sense in retrospect. 

The lattice area depicted is the area of greatest stretch, especially the red triangle that straddles the paleo rotation plane (Part 26). The triangle is long and thin due to being stretched out almost to the tip of the stretched diamond shape. However, there are other areas nearby that show similar stretch vector signatures that are orientated at a slightly different angle from this lattice. They appear to follow subtly different tensile force vectors. They will be posted presently. 

The reasoning for the red triangle arising as a result of tensile force vectors (or stretch vectors) has been documented in the sub series (Parts 22-28) especially in Part 26. This process will be revisited soon in order to firm up the evidence for the lattice in this header photo being due to stretch.

PHOTO CREDITS

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

To view a copy of this licence please visit:

http://creativecommons.org/licenses/by-sa/3.0/igo/

All dotted annotations by scute1133.

67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 30

THE SOUTH POLE HEAD-TO-BODY MATCHES  

Upper red line- the head lobe rim shear line.

Lower red line- the body lobe shear line.

From the first picture in the new OSIRIS archive, released today, 11th December 2015.

UPDATE (14th December):

SOUTH POLE RIDDEN-UP LAYERS- KEY BELOW 

   
The shear line itself is, I think, very accurate for this distance. The intermediate pale orange layers can’t be 100% exact but I think they’re pretty close due to cross-checking lots of features. Those check features are either annotated here or less important and left unannotated. The less important ones are still useful as landmarks and pointers. 

Key:

Red- these are the two outermost long lines and they are the main shear lines on both head and body. Notice how the two lines appear to mirror very subtle kinks such as a bump on the left arm of the V and two sharp divots on the right arm. 

Pale orange- intermediate ridden-up layers. 

Orange- back perimeter of the deepest discernible layer. Its front perimeter sat against the bottom of the shear line. Orange also depicts the concertinaed-out ‘V’ on the body. This might be just one layer that’s been stretched and developed crevasses rather than several delaminated and ridden-up layers as is the case on the head. 

Light blue- shear line dyke outlets. They’ve delaminated as the successive ridden-up layers carried them up with them. The blue dots on the true bottom head rim (as opposed to the red shear line above it) are half guessed but nevertheless using the orange line and yellow dots plus visible ‘teeth’. These blue dots fit to the base of the shear line on the body and are much closer together like their counterparts on the body. The lines of blue dots on the upper layers have stretched out with the recoiling of the layers or flared/fluted as the gases escaped up the long crevice at the shear line. The base of the shear line at this point is at least a couple of hundred metres deep. You can see the steep, shadowed cliff. 

Green- outlets or sink holes.

Yellow- additional matches just inside or outside the shear line. 

UPDATE WITH ADDITIONAL MATCHES

   
Pink is an isolated line which was suggested by Ramcomet as the seating for the yellow match. My choice is the upper line due to the topology of the nesting and mini matches around and within the body yellow line (careful scrutiny needed here for what would otherwise appear to be a facile match). 

Copyright ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 29

THE ONION LAYERS THAT RODE UP ON THE HEAD AND THE RAISON D’ÊTRE FOR SERQET.  

Key
Red- ridden-up layers.

Blue- matching holes that were nested on the head rim. 

BACKGROUND 

In Part 28 the final pieces of evidence for the head lobe stretching before it sheared were presented. These were the Hatmehit V’s, the stepped feature along the sliced rim of Hatmehit and finally, the onion layers which were said to have ridden up over each other during head herniation and stretch. No annotated photos were presented to support the riding up of the onion layers. The first batch of those photos will be presented in this post. There are too many for one post. It will take several, posted sporadically between other items.

Prior to the head shear, the concentric onion layers of the head didn’t just fold forward into upright folios, as described in Part 27, they actually rode up over each other. This is because the tensile stress due to comet spin-up was pulling them eastwards towards Bastet while the two lowest layers at the head rim were still pinned to the body (the so-called vertical wall stratum and Serqet rim stratum, described in Part 26). The folding of the layers into V’s relieved some of that ‘centrifugal’ tensile stress but it wasn’t enough, hence the next option, which was for them to ride up over each other.

The riding up of the onion layers would, in notional terms, be similar to a Venetian blind, except that it would be curved around the curving head lobe. That’s not a bad mechanistic analogy to bear in mind but perhaps it’s a broken Venetian blind with some layers angling up a bit more than others, some fused and a few torn in half, riding upwards but sideways a bit as well. However, when you see it in the round, the general idea of layers riding up over each other like a blind is unmistakable.

Photo 2- regional map of the comet for orientation. 

 

FOUR RIDDEN-UP HOLES AT MA’AT/ MAFTET

The riding up of head onion layers is most evident in the form of four holes near the Ma’at/ Maftet border. The holes repeat on four successive layers.

Photo 3 shows the head lobe, including ridden-up layers with matching holes. Photo pairs with unannotated versions are numbered as one photo in this post. The NAVCAM took this picture at 90° to our usual ‘upright duck’ orientation, hence the vertical wall is facing upwards instead of to the left. It’s the obvious white area at top-centre and the head rim stratum flares out a little higher. Rotation direction is right side downwards. 

Photo 3- four holes.  

   

Light blue dots- holes that repeat on four successive ridden-up onion layers.

Two red dots- location of ridden-up features in the next photo.

Green, orange, yellow- these are the usual coloured head rim matches (Part 24) that match to similarly shaped areas below on the body. The dots are in fact just the most obvious sections of each matching area. They all join into a 1-kilometre-long matching line. The mauve match is almost completely obscured by the yellow one so it’s not shown here. 

Terracotta- the sliced facet (Part 20) which defines the southern top edge of the head lobe. 

Light orange- this broken line shows the exposed ends of onion layers that were broken off as collateral damage in the main head lobe slice (Part 20). They are hypothesised to have been pushed upwards, being on the top of the head but too near the edge of the slice to escape some damage. Although we’re calling them onion layers, they flaked away like puff pastry layers. They have left lower onion layers exposed, which are below the broken, light orange line. These exposed lower layers show up as a slightly rougher, more crumbled region than the non-flaked (but ridden-up) layers above the light orange line. That’s why this small area has been noticed as being different and therefore been designated as a separate region called Maftet. However, the reason for its different appearance (the probable head lobe slice) has not been identified by the Rosetta mission. Maftet may extend as far as the four blue dots because there’s some roughness up to that point too but Maftet is hard to see on the ESA regional map.

RIDDEN-UP LAYERS AT MA’AT

Photo 4- ridden-up layers at Ma’at. This is a close-up from the above photo but it focuses on a section of Ma’at on the border with Serqet. This photo is centred on the two features dotted red in that photo and has been swivelled 90° to ‘upright duck’ configuration. 

   

Mauve- this is the very tip of the mauve head rim match peeping out from beyond the yellow match. Together, they form the tips of the pillars of the recently named Alexander Gate.

Dark green- perimeter of two matching features belonging to adjacent onion layers that have ridden up; and dark green is also used for the outline of the green head rim match itself, at the bottom on the rim line. The first and second ridden-up layers were nested over the head rim match before the stretch event.

Red- part of a curved, finger-like feature, which is an extension at the bottom of the first ridden-up onion layer. It’s picked out because it has a well-defined dark perimeter, which will be seen to be significant for the body match described further down. 

Yellow- this is a quasi-rectangular area. It has the same width as the finger-like protrusion on the layer below it. It looks as if the two yellow dots at the bottom of this rectangle would have fitted somewhere close to the top of the red protrusion below, most likely at the green dot on the sharp turn into the finger. Indeed, in photo 11, further down we’ll be able to see the curved end of the matching finger-like protrusion below the yellow rectangle. This is all but whited out in this view but this photo was better for showing the general outline of the nesting layers.

Light blue- a triad of three small, scalloped dips. Notice there is a third set of them far above the two matched layers, denoting what is a third but smudged, matching onion layer. We know it’s there because the four holes in the previous photo dictate that there are at least four related layers. So we’ve found three of them matched a little way over, two of them very well matched. The fourth is the green head rim match itself.  All four would have been nested against the Anubis slab a thousand metres below on the body. They were sitting right inside the rocky tray of the green body anchor, nested with the green head rim match at the bottom. The tray is the same shape as all these nesting features in this photo including the green head rim match:

Photo 5- the green body match, also called the green anchor tray. 

   

The green head rim match is slightly smaller than its two matching layers that rode up above it. That’s because it sat at the bottom, inside the tray and its two companions were nested on top. They sat over the sidewalls. That ‘red’ protrusion above on the head probably sat in the dark, rounded dip along the front of the tray. The dip is favourably positioned and shaped to accommodate it. You can also see it is edged with the same dark-edged, rounded perimeter as is exhibited on the red finger tip on the head. Photo 11, later on shows the upper protrusion of the two ridden-up layers to be scalloped as well as rounded, which lends support to this dip accommodating it. See also the ‘advanced’ annotation of the green anchor tray at the bottom of this post.

Photo 6- a view of the dark green head and body matches together in the same photo. It’s inserted here just as a check that the green head and body matches are indeed the same size and shape and one above the other.  

 
Below is another photo of ridden-up layers showing different matches and extra annotations to the matches above. It’s one photo, presented with five different annotations so as not to clutter it up with dots. The first one is unannotated as a dot-free reference photo, making six altogether. The second one just shows the paleo rotation plane for orientation purposes. The other four show the ridden-up layers. 

Photo 7- (first of set of six), unannotated 
 
Photo 8- Paleo rotation plane   
Brown- Paleo rotation plane (Part 26)

Dark blue- key parts of the current rotation plane. The rest is left out so as to be able to focus on the paleo plane, which will become more and more important in upcoming posts. That’s because the paleo plane held sway during the riding up of the head layers and the current rotation plane wasn’t in any way involved at that time. The current plane is taken from the shape model equator on the ESA Rosetta blog. The paleo plane is judged from the 10 symmetrical stretch signatures (Part 26) running from Apis to Bastet and on down to the head lobe hinge at Anhur. Seeing as the stretch signatures in the photos are so symmetrical and at higher resolution than the shape model, the paleo plane is easier to judge than the current plane. They’re both accurate to about 100-150 metres, which translates to about 2-3 dot widths for the paleo plane due to the viewing angle and about 3-4 dot widths for the current plane.

Photo 9- onion layers.  
Red- onion layers that have ridden up over each other.

Light blue dots- four holes that have ridden up with their four layers and were once nested together. Note that these are not the same four holes as in photo 3. They are a second batch, sited further along towards Serqet and were as good as completely whited out in photo 3. Here, they are thrown into relief by different lighting. The other four holes are in shadow to the bottom-right. These holes correspond, for the most part, to the same layers as the other four. They are just further over and slightly more angled away from the paleo rotation plane due to being forced over. We’ll see why they were forced over further down. 

Photo 10- tracking the movement of the second batch of four holes.  
Large light blue- the same four holes as in the photo above.

Small light blue- these define lines of travel up the head lobe for the four holes. They are actual, visible lines perhaps more visible in the unannotated version. They link the outside edges of each hole. The reason for the extra line in the middle is that some of the holes seem to have a double-lobed shape, the apex of which is also linked by one long line. The lines look like scrape marks but could be anything. For the most part, the two outermost ones follow the perimeter of a long depression that appears to have extended down from the originally nested four holes. The depression is the same width as the holes. So if they rode up, the depression rode up with them too. It would have gone from being one depression to four concertinaed-out depressions, which together now form a long, shallow trench. 

The double-lobed holes and the line down the middle seem to suggest a slight sideways component to the sliding of strata. That would be a vector in the direction of Ma’at (in shadow, bottom right) while the bulk of the sliding was up the head lobe. Combing the two vectors betrays the direction of slide on this side of the rotation plane which is essentially in line with the rotation plane but biased slightly to the right of it. We’ll see in a future post that the layers riding up to the left of the rotation plane were biased slightly to the left in mirror fashion. This mirrored behaviour is entirely consistent with the head lobe layers folding into V-shapes under the tensile force of centrifugal spin-up (Part 27). The V’s had their apexes centred on the paleo rotation plane (Parts 26 and 27). The riding-up layers would exhibit this slight sideways sliding tendency as they were pulled forward, up the head, but were forced out sideways slightly, along the arms of the V’s. We can see this behaviour very clearly in photo 9, above. The red-dotted onion layer rims have not only ridden up but also spread towards the right of the frame, away from the rotation plane. 

Photo 11- vertical wall matches and more green anchor matches.   
Light blue- matching lines at the top and bottom of the vertical wall. The curve at the bottom isn’t very obvious here but is more so in other, more top-down photos. These will be shown in a future post because this curve, plus its ridge extension curving down to the orange match fits to the back of the fracture plane (Part 26) in Hapi, 1000 metres below. 

Dark green- everything in dark green relates to features that have ridden up from the green match on the head rim. As stated above, all these similarly shaped layers were nested in the rocky, green anchor tray on the body before the head sheared. The green head rim match is delineated in small green dots at the bottom and is in partial shadow. 

Large dark green- this dot is the centre of the head rim section of the green match and is the classic position for all single green dots when they depict the green match from a distance in other posts.

Medium-size dark green- these three dots depict an important match. It used to be attached to the end of one arm of the green anchor tray on the body and is now visible in its delaminated form, a bit like an exploded diagram of the original lump. Each central green dot is surrounded by very small dots to depict the perimeter of each component. The lump broke off and rose with the head. Before the shear, when the layers were riding up, it rode up with them, leaving a small residual lump at the anchor. This is angled away from us slightly in this photo hence its narrow appearance. It appears that the main part of the lump was deposited at the base of the vertical wall because that’s where its ridden-up layer decided to stop. The layer at the top of the wall exhibits the hollow from which that lump broke out. If you replayed the movie backwards, the vertical wall would be seen to slide down and out of view behind the rim stratum that has the lower blue curve. The top curve and bottom curve would nest together just before it disappeared behind the rim stratum. The wall would not only slide downwards but sideways towards us while the rim, too, eased towards us in sympathy with it (because the rim stretched away from us with the wall base just before head lift-off). 

In reversing down at this angle, the hollow at the top would scoop up the main lump (middle green dot) on its way down. Then the two together would slide down a further stratum level to nest over the green head rim match. They would come to rest, slotted over the small residual lump sitting where it always had been, at the anchor. However, both lumps and the hollow travelled up with the head after shear. That means there was nothing of this broken-off end of the anchor left on the body. 

Note the scalloped nature of the red finger next to the main lump in the middle. This finger matches the one already mentioned above in photo 4 and that one is seen here too, just above the shadowed head rim match. The scallop for the upper finger was mentioned above as making it a strong candidate for sitting in the dip that is sited in front of the the green anchor tray rim (photo 5). That’s the only physical place it could fit when these layers were nested in the tray. So, with the scalloped upper finger nesting over the curved, black-edged bottom finger, they must have sat in the only scalloped, curved, black-edged location they possibly could have- the dip at the front of the tray.

Photo 12- the ‘bright green ridge’ extension matches.  
Bright green- these three matches are annotated in bright green because they’re a continuation of the very straight ‘bright green’ ridge that extends along one perimeter of the slab A extension on the body (Part 22). That ridge was described as extending up the first rim stratum above the mauve head rim match in Part 26 and you can just about see it here, a white strip extending down from the lowest of these three matches. It’s the white strip on the horizon. Although it’s only just visible here, it has a square cross section just like its rectangular, recoiled counterpart on the body (red triangle recoil, signature 6, Part 26). Its top end is annotated bright green and appears torn. 

The second match is at the top of the vertical wall. Its tear that matches the ridge isn’t visible here because it’s facing down at the ridge end it tore from. If you slid the vertical wall down behind the first rim stratum, as described above, the two would join. This second match does, however, present to us the tear that married to the third match above it. It’s a long tear, directly facing us. 

The third match is at the other side of the Nut depression. We’ve already discussed how the Nut depression isn’t an eroded section of Serqet (as the OSIRIS regions paper suggests), but the revealed top of the wall due to the stratum above sliding up the head. So the third match belongs to the slid stratum above the wall. It was formerly joined to the top of the wall, just like the first match below it, but in this case it was joined to that long tear on the side we see. There’s a spidery ridge line along which it slid and, if you were to reverse the slide, you would see it slide along that middle, wall-top match and click into place. This third match is clearer in top-down photos and will be revisited in more detail in future. Its tear is of course facing away from us so it doesn’t look very interesting here. 

THE VERTICAL WALL PUSHED THROUGH THE LAYER ABOVE.

Since the lower, rim stratum match in photo 12 joins to the top of the vertical wall and the upper, Nut match joins to the same lump on the top, we come to the inescapable conclusion that the head rim stratum and the layer above Nut were once joined together as one stratum with the wall out of sight. The wall layer was buried one layer down beneath this single upper layer. There is also evidence for this on the body, 1000 metres below. It means that the wall tore its way through between the two layers and tipped upwards under the tension of stretch so as to become more vertical when viewed in upright duck mode. It had a greater tendency to do this than any other ridden-up stratum because it had its two ends ripped away at Anubis and Ma’at (when the wall and Ma’at were on the body). 

The mechanism for this surgical excision of the wall from its respective layer is quite simple and based on the clear stretch signatures presented in Parts 22-28. It will be explained in an upcoming post. 

The tipping-up of the wall also explains its wide, smooth expanse. Possibly even riven-looking. It’s because it was formerly the upper facet of an onion layer stratum that was buried in what was formerly the single-body comet. 

We can now go back and see how the vertical wall pushed right through the onion layer above it. Photo 13 is photo 3 reproduced with different annotations and shows the vertical wall side-on. 

Photo 13- the vertical wall pushing through the onion layer above it. This happened when still attached to the body while the head lobe was herniating under the tensile stress of stretch. So we are seeing the result, set in the head lobe after shear and will now reverse the process in our minds’ eye.  
Bright green- the same matches as those shown in photo 11. Notice how neatly symmetrical they are in their separation when seen here in profile on the horizon. They’re spread along a line almost parallel to the paleo rotation plane (photo 8), as one would expect if they separated from one central lump under the tensile force of spin-up. 

Light green- one of these lines runs along the bottom of the vertical wall which is the same as saying it runs along the top of the rim stratum. The other one runs along the back of Nut, which is defined by the onion layer that moved aside to make way for the wall pushing through. When that layer meets the rim layer back at the top of the wall, those two layers become one single layer. 

The two light green lines form a very symmetrical shape with the top rim of the wall running right down the centre. The top rim of the wall is of course the join line where the two sections of the single onion layer will zip back together. The three bright green matches are perfectly silhouetted here, which helps to visualise the process. 

If you played the movie in reverse and pressed the vertical wall back to where it used to be, under the surface, you would see the two outer, bright green dots move towards each other and merge with the central dot. That means the Nut layer and the rim layer would close together over the wall, meeting at its top rim, with all three bright green matches nesting together in the middle. 

The two outer, sliding layers would become the one onion layer they always were when on the body. That single layer used to sit above and parallel to the wall when the wall wasn’t tipped up ‘vertically’. “Sit above” in this case means in the conventional strata sense i.e. with the wall stratum merged back with its respective onion layer, sitting deeper into the comet and the zipped-up layer sitting flat on top of it. It doesn’t mean ‘above’ as in ‘higher up the head lobe’ as we’ve been using the terminology for the ridden-up onion layers. Both layers, the wall and the zipped layer above it, sat flat on the body before shear (although there may well have been a proto-lump).

Today’s impressive-looking wall was therefore once just a buried section of an ordinary onion layer. 

During the ‘reverse replay’ the two outer layers would perform their meeting back up in a perfectly symmetrical, equidistant slide. The two outer, bright green matches close either side of the central match as we view it here, one clamping in front, towards us (the Nut component) and one behind, away from us (the rim/ridge component). This, along with the fact that the long Nut match is sitting wholly within its respective layer section means that the two sections of the layer zip very tightly back together in the middle, along the top rim of the wall. 

Photo 14- the vertical wall pushing through the layer above it now explains the ridden-up layers in photo 4.  
Red- these three layers are (a) the two ridden-up layers from photo 4 that were carefully outlined along with the red finger and three blue scallops and (b) the smudged third layer that wasn’t outlined in that photo but had its matching three scallops annotated. Now that we can step back and see the vertical wall pushing through, we can see that these three layers were delaminating around the edge of the split so as to accommodate the wall coming through. 

Regarding the main section of wall pushing through, there are just two sections of one single layer which unzipped above it and slid back spectacularly to where we see them today. But these three red-dotted layers at the side can now be seen to be extra delaminations concertinaing out across the smaller gap at the end of the split: one is from above the rim stratum section, i.e. from above the green head rim match; one is from below the Nut section; and one (the middle one) was sandwiched between the two. All three were nested at the rim over the green rim match and the full nest of four layers originally sat in the anchor tray on the body, as described above. 

ADVANCED ANNOTATION OF THE GREEN ANCHOR TRAY. 

Photo 15, below, is another view of the green anchor tray to complement photo 5. I’ve realised that those readers like Marco Parigi and Ramcomet who are very familiar with the matches, shear line and stretch mechanisms are capable of taking on much more information. So we’re going to start seeing more advanced annotations that are set aside or at the end of posts. They won’t be necessary for those readers new to stretch. The other photos in the post will be sufficient but careful scrutiny of the advanced pictures, and their unannotated versions will probably accelerate one’s understanding of stretch theory. 

Photo 15 has a lot more information than photo 5, including mini matches, along with narrative matches for the ones that would be obliterated by dotting. You’ll be referred to photo 4 a few times for comparison and to photo 5, both of which are reproduced here first:

Photo 4 reproduced.  
Photo 5 reproduced.  
Photo 15- the green anchor tray with the head layers shown nested on it. 

   
I believe most of the annotations in the tray are very close to where they sat but they can’t possibly be exact to more than about 20 metres due to the matches themselves stretching. The tray is about 350 metres across.

Large dark green- the classic annotated position of the green body match/anchor tray. Notice how it’s set back from the outer green line which is now reckoned to be where one or both of the layers on the head sat.The large green dot in photo 4 would sit exactly on top of this large dot. 

Very small dark green (full zoom needed)- this line runs through the large green dot because it depicts the perimeter of where the head rim green match used to sit. Not to be confused with the four lime green dots that run parallel to and inside the nearside (see below).

Medium dark green- this is the perimeter of the upper layer(s) that slid up on the head. It’s set to the outside perimeter of the tray. For much of its path it follows an actual line.

Red- this is most probably the seating of the red end of the finger protrusion in photo 4, as also shown in photo 5. (Red is also used for the continuation of the shear line towards us because it’s been the traditional colour used for this section since Part 17, March 2015).

Yellow- the classic head lobe shear line going off into the distance.

Orange- the orange body match.

Light blue- these three holes seem to correspond to the three scallops in the ridden-up layers in photo 4. But in retrospect, the upper one is probably too far over. They are also visible in photo 5 where they are out of the shadow and show the same elongation as those on the head. Those three in photo 5 are more bunched together. There is an extra, faint one on the head on one layer which may correspond to this ‘misplaced’ higher one here. However, we’re right at the limit of resolution, not due to pixel size but due to the fact that these matches aren’t mirrored matches like the classic head rim to shear line matches. They’re bleeding through layers, like others we’ve seen before and so they change shape as they do so. 

Lime green- these four holes are more like bi-lobed grooves running out to the small-green dotted perimeter. These four grooves would form mirrored teeth and dips along the corresponding perimeter on the head rim match. You can see three of them in photo 5 (unannotated version is best). They’re not dotted due to risk of being obliterated because they’re small.

Red- the continuation of the shear line as depicted in red in Part 17 but getting firmed up here due to seeing more close-ups of the corresponding head rim shape (including photo 4). Remember that if you are comparing the exact head rim line to the classic shear line on the body you follow the very small dark green dots inside the tray round to join the red line. The outer green line shows the line of the ridden-up layers and in that respect it doesn’t show the true shear line that broke away last of all. Satisfyingly, both green lines merge at the start of the red line. 

There’s a rope-like or root-like feature inside the tray. It’s very obvious in photo 5 but here it’s in shadow except for the very nearest tip peeping from the shadow (second and third lime green dots up). You can just about see it in the shadow here but if you go to photo 5, fix the shape in your mind and compare it to the head rim match, you can see it on the head rim, photo 4, slightly more squared than it is in the tray (another bleed through match). It involves careful scrutiny of how the end nearer the orange match bends round to follow the perimeter of the green match on that side. It does so both on the head and inside the tray on the body. It also does a dog-leg towards the other side of the head rim match just like it does in the tray. 

CONCLUSION

The sub series on head lobe stretch before shearing ran from Parts 22 to 28 but this Part furnished the photos for the onion layers riding up. So, with this post, the series that was started last May with the express intention proving the existence of onion layers riding up over each other, has concluded. Except this is just the start. This fact of riding-up layers opens up an Aladdin’s cave of mechanisms leading to an explanation for the morphology of every region and many sub-regions on the comet. Or rather, since this blog has already explained the large-scale morphology for every region except Ash, we’ll be moving on to explaining the differing morphologies within each region- as well as explaining why Ash looks so different from the rest of the regions. Every explanation is related directly or indirectly to the stretching of 67P.

FUTURE POSTS

There are many more ridden-up head layers that match. These will be posted between other items. Just the layers described in this post throw up all sorts of implications for what was going on in the body lobe when the layers were still attached there. This will probably be addressed before more layer matches are posted. 

PHOTO CREDITS

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

To view a copy of this licence please visit:

http://creativecommons.org/licenses/by-sa/3.0/igo/

All dotted annotations by scute1133.