67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 36



Among other things, this post slowly stumbles towards the original location of the delaminated sink holes, somewhere inside the left hand side of the bottom scallop. That’s pretty close anyway (to within around 100 metres) but the location became more crystallised even while writing. At the end, I suddenly realised where the exact location was. Instead of tidying it up, I’ve left it as is. So there are some very small errors in the body of the text regarding this issue and those are corrected in the last section that identifies the exact original hole location. Leaving in the slightly erroneous path taken sheds light on the reasoning to arrive at the correct location. 


The cove on the head lobe with the three scallops and holes is a bit of a chameleon. It appears to change shape and character when viewed from different angles and under different lighting. The bottom scallop was partially nailed down in Part 35 but we could do with some more views of that scallop and the other two above it. So before we carry on with a more in-depth analysis in future parts, it would be as well to post a few more photos from different angles so we can see what the cove actually looks like.

In different photos, the scallops and holes seem to move or disappear altogether. This is entirely due to the viewing angle and lighting. They remain in the same places all the time. There are four annotated photos below, which view the cove from different angles. There’s also a fifth and sixth further on down, both of which are the Part 35 header photo reproduced with different annotations.

In the photos, the four yellow lines denote the ribs between the scallops including the top of the top scallop and the bottom of the bottom scallop, which is the head lobe rim. The four lines enclose the three scallops. The three light blue dots are the three holes that delaminated from one hole on the body. That bottom hole was probably more like a fissure, pressed against the body before the head sheared (see Part 35). 

As stated in Part 34, all three scallops and holes were concertinaed down on top of each other when the head lobe was still attached to the body. This will be elaborated on in Part 37. There’s more analysis of these four photos further on down. It might be worth glancing at them, reading on and then going back to them. Each one is presented along with its unannotated version.

It’s probably best to look at the dotted lines and holes and then cross-reference to the unannotated versions so that you can start to identify the subtle features that delineate the ribs and hole locations. That includes ridges, dips and lines that are next to them, acting as nearby markers. That makes it easier to pin them down in other photos.

Photo 2   
Photo 3

Photo 4

Photo 5 

Photo 5 key:

Three larger light blue dots- the three delaminated holes.

Small light blue- the apparent perimeter of the bottom scallop hole, which is a rather flatter hole. This is more like simple scouring at the bottom of the hole and the ‘perimeter’ is really the line swept by the upper set of gull wings that delaminated from the lower set. There’s a longer, narrative key for photo 5 further below that explains this in more detail. 

The top rib of the top scallop probably extends further round on either side because there are two obvious ridges, one either side of it. However, any possible extensions haven’t been annotated because they only vaguely match the curve below them whereas the central portion matches better. When you look at all three scallops you can see that the top rim did somehow seat down on the one below because it’s the same length and roughly the same height above the next rim or rib down as all the others are from each other. There are probably yet to be identified mini matches along those two flanking ridges at the top. This top rib was also on the cusp of other cross-cutting movements that smudge the curved signature anyway. Those movements will get an airing in a future post. 

The view from below in photo 5 seems to show the top hole as being too close to the middle one and also shows what looks to be the ‘correct’ top hole nestled under the ridge, further up. However, the one under the ridge isn’t a hole but a shadow. If you trace all the spidery lines leading from the actual top hole, they are replicated in the other photos where it’s obvious as the top hole of the three. This apparent anomaly is due to the undulations of the ridden-up or delaminated layers being exaggerated by foreshortening. That makes the top hole look as if it’s much lower down and almost kissing the middle hole. 

There is an isolated fourth hole somewhat further over to the left too. That’s not part of the scallop delamination but it’s almost certainly the result of a horizontal delamination along the shear line. This horizontal delamination will be dealt with soon. So this fourth hole may have delaminated horizontally (then up one layer) from the same fissure as the main three. Or even from the horseshoe crater just next to the fissure. 

The OSIRIS papers have the fourth hole as being one of three obviously round holes, the other two being our middle and upper scallop holes. That leaves the bottom scallop hole, which is admittedly more of a scouring and ripping apart at the bottom of the original hole. That’s not been identified as a hole by OSIRIS for understandable reasons. But it was at the bottom of our delaminated hole and that’s why we are calling it the bottom member of the three holes as well as being their original location. 

The left hand extent of the bottom yellow line appears to protrude out further than the other three. That suggests that the second rib (the bottom rib of the second scallop) sat down onto the first one with its end a little way in from the end of the first one. That is indeed the case. This is more of an annotation choice than a physical anomaly: the bottom rim includes both its scallop and its scoured-out hole base (which is rather whited out hence being dotted around its perimeter). But the upper scallops are annotated separately from their holes. That’s because the two upper holes are very distinct as holes sitting right next to their slightly shorter scallops. However the hole-plus-scallop length of the two upper formations is about the same as the bottom one. 

The confounding issue that puts the bottom hole inside the bottom scallop and upper holes outside their scallops is the delaminated gull wings. Those run from the bottom yellow curve tip on the bottom rim, up at 45° to the middle hole next to the second curve or rib. This is the third set of gull wings that delaminated upwards from the two sets below it. One of those two lower sets was on the head rim, the other, on the body. The head rim gull wing set corresponds to the first five yellow dots of the bottom line but there’s also a curved extension from that fifth yellow dot to the fifth small blue dot up from the bottom. That curve is whited out here (it’s very clear in photo 6, below). The classic gull wing set on the head rim is dotted in small green as well as yellow. That set fits to the body without the curved extension and to the third gull wing set above, with the extension. You can see the dip in the middle, making them gull-shaped. The 45° set is also dotted green and they originally sat sandwiched to the rim set, including the curved extension. That means the top green dot of the ’45° slope’ used to sit on the fifth small blue dot (see the narrative key for photo 5 for a close up of this exact spot and the visible curve extension running up to it). This in turn means that if you reverse the stretch, the second yellow line tags along with the top green dot and also ends up a fair way inside the curve of the bottom yellow line. That makes the middle blue-dotted hole sit directly over the bottom hole and inside the bottom yellow curve as we’d expect. That also means that yes, the end of the second rib curve would indeed stop short of the bottom rim/rib curve end if reseated.

Of course, the scallops got stretched about a bit as they herniated away from the body (remember this has to have occurred before head lobe shear and full-blown stretching of the neck). You can see a small tendency for the scallops and holes to be directed towards the comet’s long extremity as well as upwards from the body. That means the top scallop and hole are slightly biased towards the Hatmehit/Bastet border, which is at the long axis extremity. That induces a slight curve to the left along the cove length. 


This is the longer version, explaining aspects of that photo in more detail. 

The bottom blue hole has its perimeter dotted light blue because it’s whited out here. That’s because it’s squarer and shallower. It was formed by the third set of gull wings delaminating from the second set and rising above the second set during head lobe herniation. The second set of gull wings is on the head rim and matches to the first set on the body below them at the shear line (Part 5). The second and third sets delaminated due to the tensile force of stretch. Then, after head shear, they both remained on the head lobe side of the shear line while the first set remained on the body with two slurry piles oozing out from under them. The slurry piles are what shaped the set of three into gull wings. The top, third pair no longer look gull wing-shaped due to stretching upwards but they do preserve a small kink at the requisite middle point. That point is the same distance along from the left hand wing tip as the deeper kink in the second set, which is the rim set. 

The header photo in Part 35 shows a very good close up view of the delamination of the two sets of gull wings on the head and also the outgassing dyke that probably contributed to the weakening between these two layers. Here’s the header for Part 35, reproduced to illustrate this. The key for photo 5 continues after that but with heavy reliance on the Part 35 header as well. 

Photo 6- Part 35 header reproduced. Green is the delaminated gull wings, pale orange is a slid lump, mauve is four gas dykes (more on these dykes in Part 8). Orange is a mini delamination, dealt with below.     
Photo 5 (and 6) key continued: The area swept by the sliding up of the upper set of gull wings is characterised by scouring and that scouring is right next to the trumpet-shaped dyke outlet (left hand mauve line in photo 6). The fact that the dyke is trumpet-shaped at its end suggests the gases were emerging from a fairly thin dyke (which was also part of the thin fissure at the shear line) and expanding under the reduced pressure when they reached the crevice between the gull wings. Then the gases scoured their way between the two sets of gull wings as they were starting to delaminate, thereby loosening them further. So this bottom ‘hole’ of the delaminated three is really just the very bottom of the original hole. As such, it has no depth, just scouring, and the two holes in the upper two scallops formed the depth of the single original hole when they were seated, one above the other, on this spot. This flat, scoured area is more in keeping with the theory that it was pressed hard up against the body or at least, that the trumpet-shaped dyke directly feeding it was pressed hard against the body. There’s some corroboration of this on the body. Seeing as the dyke appears to have been sliced longitudinally, one might expect a mirror image of the trumpet to be found tight against the gull wings on the body. There is a suggestion of such a shape there but it’s a double-curve. If the rest of the sliced dyke exists on the body, it’s under a bed of dust. And the dust-cover discrepancy between any head and body dyke matches is due to the gravity vector being directed straight down the Hathor cliff towards Hapi. That’s why Hapi is full of dust and Hathor completely free of it, except on ‘horizontal’ ledges. So the Hathor dykes, or longitudinally sliced dykes, are as clear as day whereas their purported matches are invisible under the Hapi dust. A final comment on dykes and their uncannily neat longitudinal slicing- they probably got sliced longitudinally in the head shear precisely because they themselves caused the weakening along that exact plane. It would be like drilling adjacent holes along one plane through a block of wood. If you then pulled the two sides of the block it would tend to shear along the weakened plane of the drill holes. The two halves would sport parallel, longitudinally sliced drill holes as straight, shallow trenches- just like those on Hathor.

In photo 5 there’s an extra orange shape. This denotes a mini delamination that would have been sandwiched between the second rib (bottom of the middle scallop) and the lowest rib which is the lowest yellow line on the head rim, with the sharp turns on its right side. You can see how either side of the orange shape matches to the yellow curves: above it to the left and below it to the right. When everything was sandwiched together at the head rim, these three sections sat side-by-side more than being sandwiched on top of each other. That’s because they are laterally displaced as well as vertically displaced. This explains why the rim curve seems much longer and more convoluted on that right hand side. Once seated, the second curve or rib is slightly ‘pushed’ over to the left by the delaminated orange shape. So the second curve starts further to the left than the bottom one, explaining the length discrepancy. 

There are small chronological issues regarding the first and second yellow lines or ribs. The Part 35 header suggests the second rib (bottom of the middle scallop) was closed up, and possibly closed over rock C when rock C was sitting in the horseshoe. Perhaps it widened to the width of the horseshoe in sympathy with rock C’s slide-back and then rose. We now know the second curve was fully closed up at some point and yet today it mirrors the bottom curve faithfully on that side. There has to be a reason for that and the above widening-then-rising scenario is a tentative stab at the mechanism. 

That very straight section on the bottom yellow curve, just after the sharp turn, is the section that was matched to the similarly straight ‘hollow block wall’ in Part 18. The hollow block wall is the straight ridge sloping up the right hand side of the horseshoe crater on the body.


Photo 7- the original location of the second hole (and presumably the third hole on top of it). This is really the scoured base or bottom hole of the three delaminated holes.  
Light blue- the second hole (upper left) and its original seating at the site of the first ‘hole’ which is really just a scoured base.

Green- the upper line is the current position of the delaminated gull wings. The lower line is the location they would have been at while still attached to the head rim set of gull wings but just after delaminating from their seating on the curved extension. That allowed passage of gases from the dyke, through the fluted end of the dyke and between the two delaminating gull wing layers. 

Mauve- path of gases from the dyke, through its fluted exit, between the separating gull wing layers and ending in the middle of the hole base.

Pale orange- the lump that slid with the hole (upper left) as well as its recessed former seating next to the scoured hole base.

So the hole wasn’t exactly on top of the gull wing delamination but just above it. Above, it was stated as being sited on the area within the blue-dotted line which was the entire area left behind by the gull wing delamination. But it was sited just above that area because it was formed by gases escaping from between the gull wing layers before they’d actually separated. It looks as if the gases from the interior found their way out of the fluted dyke and between the two gull wing layers even as they started delaminating. The gases then travelled between the two gull wing sets and escaped at their open ends. On emerging from the tight channel between the two sets, the gases probably underwent sudden decompression and were able to push their way up to the surface, thus creating a single ‘sink’ hole. That hole then slid to the upper blue location under the tensile force of stretch. When it arrived at this second location, it then delaminated a second time, allowing the third hole to slide up with its third scallop. 

This means the first ‘hole’ in the bottom scallop was really just the scoured bottom surface of the hole, which then slid away in its entirety. That’s why there’s no actual hole there today but there is this scoured base signature at the end of the gull wings. The area under the gull wing delamination is also scoured but that was the feeder and not the exact location of the hole. That extra area of scouring was why it was misidentified as the actual hole base, above in this post.


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

To view a copy of this licence please visit:


All dotted annotations by Scute1133.


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