67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 28






Basically, you were right all along, for the head lobe at least. It’s like an onion albeit one whose layers have ridden up over each other in the stretch. It’s the only way you can reconcile the sliced head photo with that classic ‘flat slab’ photo from the other side. Another way of looking at it is that it’s nested cones that have ridden up. This means that Hatmehit isn’t a missing slab but a missing cone.”

(Excerpt from an email from me to Marco Parigi, inventor of stretch theory, 11th May 2015). 


This part will introduce the last three elements of the sub series. Those are the Hatmehit V shapes, the sliced facet strata and the superficial ‘riding-up’ of the head lobe strata due to their onion-layer structure.

Marco and I had been labouring under a false premise that the comet was composed of straight, even layers of strata. This was based on deferring to expert opinion and against our own judgement that it was composed of onion layers. It was the realisation that the head lobe did have an onion-layer structure, after all, that prompted me to reanalyse the head in even closer detail. Hatmehit had to exhibit evidence of the onion-type structure. This led me to trace the sliced facet strata lines up to the Hatmehit rim, over a curious stepped feature and into the crater itself. There, I found that the same lines could be traced to the Hatmehit V’s, which are almost indiscernible, spidery lines in the NAVCAM photos. 

Before we continue with the stepped feature and the Hatmehit V’s, here’s the usual regional map photo of 67P to help with navigating around. Also, the one showing newly named regions on the south pole. 

Photos 3/4- the regions.  


The new regions on the south pole were in winter darkness till May 2015 and named around August. The sub series deals with all these areas but doesn’t name them as regions because names had already been coined in the absence of region names. These are the ‘sliced facet’ on the head lobe and the head lobe hinge (both in Part 20). The hinge is divided into two gouges. Those are the head lobe gouge and the body lobe gouge. These are named thus because they are morphologically distinct with explanatory mechanisms for those morphologies. 

The region of Wosret comprises the sliced facet (where the name is printed) and the head lobe gouge (bottom-right shadow). Anhur comprises the body lobe gouge at right as well as a pan-handle extension to the top-left. That extension is where the head lobe tipped southward temporarily before hinging properly at the forward gouges. The southward tip is more conjectural than other observations made in this blog. 


Photo 5- the stepped feature on the Hatmehit rim with the fracture planes shown linking to the steps (the fracture planes, yellow, are in shadow but visible in other photos- this shows the actual steps, red, in the best resolution). 

First of all, I traced the sliced facet strata to the Hatmehit rim where it was apparent that they caused the stepped feature that runs all along the straight side of the crater. The straightness of the rim at this point, in contrast to the rest of the curving crater, is due to the head lobe slice itself (Part 20). It’s the top of the slice and, if you recall, it’s not really a slice but a successive cracking of strata up the side of the head, probably due to uneven tipping of the head onto its south pole rim on shearing. The fact that the force on the rim was upwards explains the ruggedness of the stepped feature. It’s frayed in a manner of speaking. Another reason it’s frayed is because the Hatmehit slab was torn away from it, indeed, possibly kicked away by the strata cracking their way up the side.

The stepped feature is formed that way because of the frayed, sliced facet fracture planes emerging at the top of the comet. They poke up in successive steps.

This meant that the sliced facet fracture lines turned the sharp corner at the Hatmehit rim and traced lines along the inside 90° turns in the steps. So we could now jump into the Hatmehit crater and see them coming across the steps from the other side. They then drop down from the step sides (which are somewhat protruding upwards in a wide ridge) and into the main crater. Inside the crater, they form the Hatmehit V’s.



Photos 6/7- Hatmehit V’s including unannotated version for an uncluttered view. 

Tracing the fracture lines from the steps down into the Hatmehit crater, I realised they were linked to extremely fine lines in the dust that formed the spidery V-shapes. They were stacked across Hatmehit in a chevron pattern whose centreline ran close and fairly parallel to the rotation plane. 

I assumed the spidery V’s to be outgassing signatures in the dust, betraying the concentric layers below. Except they weren’t concentric layers, more like upright, folded folios. The V’s were assumed to be the torn-off tops of the folios. The Hatmehit missing slab was the part that was torn away and this implies that it was probably a stubby pyramid or cone shape of stacked V’s. It would therefore have been the pointed end of the stretching comet, and not a single-stratum slab.

The stepped ridge and Hatmehit V’s will be elaborated on in a future post, with more photos. In the meantime, it should be stressed that some of the V arms near the steps look like rock trails- rocks rolling from the steps down into the dust. This is not the case for two reasons. Firstly, most or all the V lines can be traced from the Hatmehit dust, up to and right across the steps- the fracture lines mentioned above. Secondly, the V arms that look like rock trails have corresponding northern arms of the same spidery character. These are at the correct corresponding mirrored angle in relation to the paleo rotation plane that runs right through the middle of all the V apexes. 


It was the discovery of the Hatmehit V’s that led to a review of the head lobe and whether there were more V shapes extending down Ma’at. Of course, there were and that led to a domino-effect of related features snapping into place down the head lobe, through Serqet, down the neck and across the body. All the way to the curious, rectangular lump of crust named Apis. The centre of Apis is at the exact opposite end of the long axis from the centre of the first Hatmehit V. 

All these features and their single causal mechanism- stretch- were then described in the sub series from Parts 22 to 28, this current Part. They were described in reverse order to their discovery. That’s because the observations running from top to bottom of the comet led to understanding the sub-mechanisms causing those features. It was easier to describe them running from the body, up the neck, up the head lobe and now, across Hatmehit. The reason for that is that the anchor for the V-shapes on the head (the ‘vertical wall’) was originally seated on the body. The evidence for its existence as an anchor (the red triangle, slab A extension and Anubis slab) are also on the body. So the sub series started with the slab A extension on the body. 


 Photo 8- onion layer configuration. Rotation direction is head lobe towards the right. The paleo rotation plane runs through the centre of the V’s.  

Yellow- sliced facet strata lines.

Red- (a) the Hatmehit V’s are the first four from right to left); (b) the more curved head lobe V’s are the rest of the V’s, to the left of the Hatmehit V’s. 

Fuchsia- An incidental aside, this tiny dot to the left of the righthandmost yellow dot is the OSIRIS location for Philae. The CONSERT location is in the small shadow between it and the yellow dot below.

The Hatmehit V’s can be traced to the sliced facet strata and on round the corner of the slice to the other more curved V-shapes (Part 27). Those more curved V’s run round the main head lobe. All three together, Hatmehit V’s, sliced strata, curved V’s, betray the onion layers. 

In the photo above, several Hatmehit V’s are defining the same stratum layer as their counterpart on the curved head lobe. It means you could lift off each layer like so many stacked ridge tiles- some curved, some V-shaped or a gradation between the two. They are generally facing forwards slightly rather than straight downwards. This stack of tiles or onion layers riding up over each other in the stretch are the last piece of the head lobe puzzle. This means that the two lefthandmost V’s were once contiguous. What is now the upper one (right hand one of the two in this photo) rode up over the layer below it exposing that lower layer. That exposed layer is the region called Nut. Then the next layer rode up over the one that had exposed Nut, and so on all the way to Hatmehit and beyond, up to the tip of the presumed cone. The same riding up happened below Nut as well, involving three layers between the Nut perimeter and the head rim.

There will be a separate post on the riding up of the layers, complete with matches between layers. For now, suffice to say that at least the first three layers above the head lobe rim were once stacked over each other along a broad strip. 

It should be noted that in the photo above there are two red lines on the main head lobe curve that don’t form V’s and are not in other photos in this post. This is an illustration of the fact that tracing these lines is an ongoing project. The one at the bottom of the head that disappears below the layer above, has been yanked up further by the sympathetic movement around the vertical wall. It appears to have slid two layers’ worth of slide. That’s because layers around the sides and above the wall apparently moved longer distances to compensate for non movement of the wall. This particular layer had to slide twice as far at that end and the ‘normal’ distance near the sliced facet. The other short, marooned line is in fact incorporated into the V below it in another photo in this post. In that photo, the line below this one in question is the marooned one. This reflects the small uncertainties in ascertaining what constitutes an onion layer rim in some places. 
Also, the Hatmehit V’s in the above photo aren’t exact because of white-out but based on their existence in other pictures. They are also fewer in number than in the close-up pictures above (photos 5/6) so it’s more schematic and uncluttered so as to highlight the internal onion layer structure. Tracing all the lines is a work in progress but in principle this annotation does depict the onion layer configuration as ascertained from many other photos. 

The foremost or right hand V is the Hatmehit hinge, where the Hatmehit missing slab is hypothesised to have hinged up (Part 12). It’s defined by the cliff at the eastern end of Hatmehit. The fifth V from the right is the opposite (western) perimeter of the Hatmehit crater. 


The head didn’t always exist in its present shape when seated on the body. It partially herniated from the body. The herniation presumably occurred during the latter stages of stretch but before the head finally sheared and rose atop the stretching neck. The original, notionally flatter body onion layers were pulled upwards and forwards into the curved, V-shapes. 

There must have already been some significant degree of present-day head shape in the form of a proto-lump that facilitated the process. That’s because the onion layers were bent upwards by perhaps 30°-40°, not 90°, which would imply full herniation. 

Regardless of its topologically V-shaped constituents, the newly herniated head was essentially rounded and bell-shaped. 

That describes the herniation as the comet core layers attempted to push their way through the original crust of the single body to form the head lobe. It was rather like an incipient lava lamp plume. The stretch before shearing and especially the herniation suggest that the core was not brittle but ductile, via whatever means. Mechanisms for a ductile, stretching comet instead of a brittle fracturing comet were laid out in Parts 10 and 11 in January 2015. These cited existing peer-reviewed literature on comets being lightly sintered ice pebble piles. Around that time the 3-metre ‘goosebumps’ were discovered on 67P and scientists were saying the distribution curve could go all the way down to the marble sizes that had already been modelled. 

Looking at the ‘upright duck’, the foremost and topmost V’s at Hatmehit were subjected to the most ‘centrifugal’ force and folded into the most acute V shapes- the Hatmehit V’s. The most rearward V’s were subjected to less centrifugal force, remained almost circular and stayed pinned to the body at Serqet. All these V’s being described are onion layers. So the V’s, or onion layers in between the pinned rim and Hatmehit rode up over each other in the prograde stretch direction i.e. up towards Hatmehit. 

This sequence of events caused the present-day skewed-forward bell shape of the head lobe: vertical at Bastet; drawn smoothly forward in successive tiers down the slope of Ma’at; and finishing with a stretched, curved ‘bell rim’ around its rearward rim: 

Photo 9- the skewed bell shape. 

Yellow- Bastet, the pulled-forward front of the bell.

Brown- the smooth slope of successive tiers.

Red- the flared-out bell rim. 

The riding-up of the intermediate onion layers causing the smooth slope of Ma’at isn’t conjecture. There are clear matches from layer to layer, found on at least three layers so far, four if you include their common seating on the body. These matches show that the layers once overlaid each other. They have already been researched and annotated in detail and will be put in a future post. 


The Hatmehit V’s are no different from the main head lobe V’s as described in Part 27. It’s just that they were torn off across Hatmehit (the Hatmehit missing slab, or cone, did the tearing) and then covered with dust. As mentioned above, their existence, along with the sloping sliced facet strata and the curved head lobe strata, reveal the existence of the onion layers. One should be able to trace a single line from a V shape, out of Hatmehit via the step feature on the rim, down the sliced facet, round the curved part of the head, back to Hatmehit and join up with the same V. It’s probably not quite possible to complete that tracing in practice due to dust and shadowing in photos but one can manage it for about three-quarters of the way with some lines. As mentioned above, this will be looked at more carefully in a future post. 


An alternative way of looking at the south pole header picture is if you wrap about 20 coats or capes round the back of a chair. They’d form a stack of concentric layers. They would be quite tightly folded curves round the chair in the middle, getting bigger and fatter as they progressed out to the outer layers. The chair would be hidden under something resembling a semispherical dome but with quite a flat, vertical front. That’s because the coats wouldn’t go right round the chair, their ends would all flap forwards. They would be folded into V-shapes (looking from above) going from tight, nearer to our Hatmehit V’s, to fat, curved V’s for the outer coats. 

This is actually the case on the comet- the onion layers don’t go all the way round the ‘chair’ in a real cone or half-onion. They’re folded around it with their two ends, (the buttons and button holes) facing forwards at Bastet and curving round and downwards towards the body at Ma’at. Once fully curved round, they face down to Babi 1000 metres below. The same thing happens at the south pole but the signature is almost completely smudged by the head lobe slice. Presumably, all these strata would have mirrored those we see at Ma’at, above Babi. 

Incidentally, it may sound confusing talking about Ma’at at this end of the head lobe, considering the fact that we were talking about it when describing the other end too. That was the ‘smooth slope’ of ridden-up layers down the Ma’at slope between Hatmehit and Serqet. Ma’at just happens to be a very big region, curving 180° round the north side of the head.

Photo 10- onion layers at Bastet, Ma’at and south pole. 

Red- strata facing the viewer. These are the ‘coat buttons’ on one side of the centreline and ‘button holes’ on the other. There are eight lines to right of the centreline, denoting 7 strata and three to the left of centre denoting two strata. The rest of what you see on the left side is the sliced facet of the south pole. If we were to stick the sliced portion back on, it would presumably exhibit a mirror image of strata to those we see on the right, an extra five or thereabouts. 

Just as a check that the rest of what you see on the left is the sliced facet, here’s a link to Brian May’s site, which shows a stereo 3D view of the photo above (along with another photo from a very close viewpoint).

Photo 11- same as above but with additional annotations. 

Four larger red dots along the top rim- these correspond to the Hatmehit hinge V, the last V on the head. It’s actually just behind this point but you can still see the sympathetic V shape in the curve of the Bastet/Hatmehit rim. You can also see how this tip of the long axis appears to be starting to taper to a cone shape. If there was a cone then it has now departed in the form of the Hatmehit ‘slab’ or ‘cone’.

Brown- paleo rotation plane. As you might expect, it’s the dividing line of symmetry in what is an impressive mirror image of strata lines forming V shapes. This time, they’re at roughly 90° to the V’s across Hatmehit yet, paradoxically, they are formed by the same strata. You could say the V’s across Hatmehit are the bent-round coat collars albeit large collars, and these V’s are the buttons on one side and holes on the other, draping out sideways as they drop down. 

Blue- part of today’s rotation plane. 

Photo 12- the same strata lines as those on the right of the centreline in the above photos but viewed from the side, above Babi. 

This view is at almost exactly 90° to the two above so the paleo line is running roughly down the left hand silhouette of the comet.

Now, if you tipped our chair forwards a long way or even stuck it on a pole and spun it up in zero gravity, the coats would ride up over each other with the ‘centrifugal’ force. That would be the successive tiers down the Ma’at slope towards Serqet. The only thing remaining to complete the analogy is that someone came along with a machete and sliced vertically through one side of the coats, revealing their sloped strata configuration within, along the south pole. 


It’s beyond the scope of this post to discuss in detail exactly how the strata facing us in the first two Bastet photos above came to be curved round and upwards to focus on the Hatmehit hinge. But you just might’ve guessed already. They tore away from the body and stretched upwards. The stretch vector is as clear as day in those photos: the nearer to the long axis extremity, the greater the centrifugal force and the greater the consequent curving up towards the tip of the long axis. That point is the Hatmehit hinge and everything in the first photo is focussed right on its central V apex. That exact point is the long-axis extremity of the paleo rotation plane. This could hardly be more clear as a stretch signature. 

Although we’ll still call the head lobe half an onion, we can just bear in mind the coats-on-chair structure. Also, on the comet, the ‘chair’ appears to be tipped forward quite a bit, judging by how sloped the strata are on the sliced facet. The buttons, or button holes, are facing more down towards the body than towards Bastet (or were before they were sliced off on that side). 

However, as mentioned above, the strata curve round and up at Maat/Bastet after having faced downwards along the Hathor cliff. So we can only assume that, with the stunning symmetry displayed so far by this comet (due to stretching) the same was the case for the sliced strata on the south side before the slice.

There’s a hint of this in the first Bastet photo. It’s those two surviving layers of forward-facing stratum on the left of the centreline which is the paleo rotation line. And of course, the only reason the strata face downwards along Hathor and to an extent at Babi is because of the head herniation pushing the originally flatter onion strata up into curved V shapes. They used to be parallel to the missing slabs, A and B, on the body because those are the slabs they tore from. This applies to at least the top three layers on the head above Babi (two matched already, one to come) implying that slab B, Babi, was at least three strata layers thick. The two already matched are those in Part 6, published nearly a year ago. 


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

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All dotted annotations by scute1133.