This post has been written with the hope that one or some of the end-of-mission planners might be able to read it. It concerns the morphological evolution of the pits that will be examined by Rosetta as she descends to her final resting place on 67P. That will happen at Ma’at on September 30th 2016 and the moment she lands will be the end of the two-year mission.
The evolution of the pits as laid out below would perhaps point to the consideration of tweaks in the way the data is taken on the way in to land.
The pit evolution scenario described below is according to stretch theory which isn’t accepted by the mainstream. It proposes that 67P was spun up via asymmetrical outgassing which itself isn’t controversial. The controversial part is the suggestion that this spin-up caused the comet to stretch into an ellipsoid, then allow the head lobe to herniate from the body and finally, shear away from the body, rising on a growing neck (the neck we see today).
The following is related as if it’s fact so as to spare the reader endless qualifications and conditional statements. It is, of course, a hypothesis. However, there’s an abundance of evidence supporting it.
The originals aren’t part of the photo numbering system. The main post follows the photos. It’s a summary of the photo explanations including further background explanation and links to other stretch blog posts. If you have any doubts or objections to what is presented in this ‘photos’ section, they should hopefully be resolved in the further explanation lower down. This is a very complex area so it would be a surprise if you got through the photos without any further questions. Hopefully the photos will be compelling enough to make you read on.
The ESA regional maps are at the end of this photo section if you need to get orientated (photos 19 and 20).
In photo 2, the majestic curve of the source for 03 is half hidden behind the head rim so it’s extrapolated with smaller dots. The evidence for outgassing from these three sources is documented in many blog parts, mainly Parts 5 and 7 and 8. There are also numerous head/body mirrored matches for this small area in Parts 1, 2, 5, 7, 8 and many more parts up to 52 and this Part. These matches completely constrain the body outgassing sources to match the 01, 02 and 03 hole positions (when the head was seated on the body). This is in addition to each source exhibiting signs of furious outgassing.
Photo 3- same as photo 2 but with the pits numbered and a new one added, dubbed 01A for convenience, and just a little bit hidden here hence the arrow. The left hand outgassing source (as viewed here from above) fed 01A as well as 01. 01 then delaminated from 01A upwards towards us and to the right. Notice how 01 is facing its body source.
These bumps are just next to the body outgassing sources depicted in photos 2 and 3. The bumps supplied the outgassing sources (see their relationship to the sources in photo 11). The bumps for the 01A/01, 02 and 03 sources are the three on the right. The fourth sitting on the left is beyond the scope of this post. Known as the ‘gull wings’ in this blog, each bump is neatly sited at the join of separated layers: four bumps betraying five layers. The separated layers are long-axis delaminations and the gases emerged from under each join hence their translational symmetry and equidistant separation.
All the bumps are more pronounced in this photo. They are slightly less so in the following photos due to a less favourable angle. However, if they’re pronounced here then they really are very prominent even if apparently less so in other photos.
Photo 5- a long shot of the head and body lobes showing the three relevant bumps and the Ma’at pits they supplied. The pits are the larger blue dots with their perimeters dotted in smaller blue (except 02 shows an extension which matches the body, shown later).
In photo 7, 01A and 01 are dotted light blue. It can be seen that 01A is just the floor of the original pit before it delaminated. Pale orange denotes a massif attached to 01 that slid from its seating with 01. The seating is also pale orange. The 01A floor can be extrapolated from the pale orange massif slide, attached to 01, which means 01 slid too by the same distance and on the same direction vector. So the massif dragged 01 from the extrapolated 01A position to its current position. The extrapolation is also fully constrained by the dark green and mauve annotations. Green are delaminated layers which, when sandwiched back together, follow the pale orange massif slide vector. Sandwiching them back together is reversing the stretch movie, so to speak. Once clamped back together, they form the lower perimeter of 01A when combined with the ridge above the upper green line that was dragged with it (see also photo 8). Mauve is a suspected dyke which supplied 01A/01 when 01 sat on 01A. The gasses forced their way between the two green layers and out into the 01A hole when 01 sat there. This may be why 01A and the area between the green lines (the mauve gas track) looks scoured and not typical of the smooth dust that dominates Ma’at. 01A’s upper perimeter is constrained by the cove delamination (Part 34) and is beyond the scope of this post.
In photo 8, the right hand arrow depicts the orange massif/blue 01 slide vector in reverse, that is, if you reversed the stretch movie. So it’s pointing from where the pale orange massif is today to where it used to be. When the massif slid up and back, it dragged its 01 hole with it from the original 01A floor. The middle arrow shows the end of the upper green delamination being seated to the corresponding end of its lower twin, again in reverse. The green dotted line has now been extended further up into a zig zag. That zig zag can be seen to have concertinaed upwards in an extended version of the two green lines described above. This zig zag is due to the cove delamination in Part 34. The left hand arrow is pointing downwards, showing that the tip of the upper zig zag point sat on the corresponding tip of the lower zig zag point. And the upper two lines of the zig zag sandwich onto themselves like the lower two described above. Therefore, the whole zig zag collapses down when you reverse the stretch movie. The two sandwiched zig zags used to be clamped to their body match. This body clamping therefore constrains the body gas sources either side of the sandwiched tip to supply the holes either side of the sandwiched tip on the head (i.e. source 01A/01 feeding both 01A and 01 and source 02 feeding 02). The zig zag delamination of course implies that the entire layer hosting Ma’at 01, 02 and 03 delaminated upwards from the lower (head rim) layer too. The zig zag is, after all, the end-on cross-section of those two layers. These two layers indeed exhibit mini-matches along from their zig zag points as well as to their expected body seating (see photos further down).
You can see that the right hand bump supplied both 01A and 01 which delaminated upwards from 01A as described above. The 02 source actually delaminated from the 01A/01 source. There’s lots of evidence for this in Parts 37-39: the opening up of the so-called shallow crater, as well as the ‘gull wing slide’ and the ‘India shape slide’ in those parts absolutely constrain the 02 source to delaminate that distance along that same slide vector from the 01A/01 source. The 03 source then delaminated in turn from the 02 source. Only then did the pits that the 02 and 03 sources were supplying, delaminate upwards with the zig zag described above. Those were of course, the Ma’at 02 and 03 pits. That’s how three sources supplied four holes (or supplied three holes and the original hole base, 01A, that they delaminated from). Of course, the gas supply happened only when the head and its pits sat right down on the bumps. It’s now 1000 metres above the bumps so most of the red lines, across the shadowed expanse of the neck, are just notional links. The red lines kissing the bump tips is also notional because the exact gas sources are just to the right of the bumps (in this view). This is because the gases were exiting to the right of the bumps i.e. out from between the delaminated layers in the reverse direction to that in which they delaminated. The exact sources are shown in the next photo.
This large amount of outgassing was along the shear line where the head rim was herniating upwards under the tensile forces of stretch and about to shear away. That’s what caused the zig zag: upward delaminating layers. The main source of gas was along the shear line (the Babi/Hapi rim) and it found its way out between the long axis delaminations hence the bumps being like mini-volcanos that are sited both on the shear line and the long-axis delamination interfaces. The difference between long-axis delaminations and upward head herniation delaminations is laid out after this photo section.
Photo 11- this is the same as photo 10 but with the exact source positions added next to the bumps or mini-volcanos. The sources are actually just out of sight because the gasses ran up the side of the Babi cliff that drops into Hapi. So we’re seeing the very tops of the sources where the bottoms of the holes or pits were originally clamped.
Photo 12- this is the same as the above two but it has a small addition. The beige dots curve up the volcano bump of the 03 source and continue up that curved half-bell shape on the head. The head rim bell shape nests perfectly over the 03 source. The 03 source looks like a scoured-out cave under the volcano bump. The bell shape on the head rim is a chimney leading to 03 and it was supplied from the cave albeit in a much more concertinaed-down configuration. The current chimney length is due to head lobe herniation which stretched the chimney. This is possibly responsible for the pockmark holes dotted up the chimney side that may be collateral gas escape routes.
In photo 13, all four bumps are annotated in dark green. They’re pairs of green dots because the first set at the top is the first set from which the other four delaminated. That’s the classic set of so-called gull wings so there’s one dot for each gull wing. The other three sets retain vestigial double bumps in sympathy. The fourth set, almost in shadow is of course irrelevant here. Yellow denotes key fiduciary points that match from head to body. You can now see the bell-shaped chimney from above (albeit in shadow but it is there) and see how it clamps over the 03 source. The full head rim to body shear line match is shown in photo 17 and the chimney is fully visible.
Photo 15- this is the same as photo 2 but with additional matches between the first two layers of the head lobe that delaminated with the zig zag in photo 8. It also shows matches between the head rim and body including triple matches for both layers to the body (in yellow).
Yellow nearest to us (lower right) is the Ma’at 02 pit’s perimeter extension that was marked in light blue in photo 5. This has a mauve feature adjoining it. The same yellow and mauve lines are seen on the head rim layer below the upper layer and from which the upper layer with the pits delaminated. This is a bled match (features repeated through layers). It’s not very apparent on the head rim layer in this photo (see original). But it is there in many photos. It’s most robust for the mauve feature and for the yellow line up to half way which is why its upper portion has smaller yellow dots. They depict a gentle trough rather than a defined line. The upper-left long spidery triangle is on the body and matches both head layer yellow lines including that extra short line on the head rim. Notice how the body yellow match kisses its light blue source semicircle in the same manner as the yellow extension meets 02 on the head. All the yellow lines are angled the same way.
The larger bright green dot on the body is the 02 source bump or gull wing set and the small green dots show the extent of the bump. The bump nested into the niche shown in bright green on the head rim. There’s a rope-like ridge running down the body from the 02 source bump. It turns and runs towards top-right in this view and casts a sharp shadow along its length. This is the rest of the delaminated layer of which the 02 source bump is a part. In part 38 this is confirmed by noticing that this line matches to the sharper ridge leading to the upper left yellow lines (the ‘trident shape’, not quite so obvious here). These are mini-delaminations of a thicker onion layer. They’re perhaps 15 metres thick. The others are visible here but beyond the scope of this post.
Photo 16- this is the same as photo 15 but includes the head rim to body shear line match in various colours. This match is traditionally done in terracotta but with yellow for the cove match. In addition here, we have the bright green 02 source bump which would normally be terracotta and also dark green going up and down over both gull wings for the first set (bump for 01A/01 source). The dark green head match is a cheat- it’s the upper line of the first zig zag, not the lower line on the true head rim. But they’re perfectly in line from this above view. The cove and its seating is yellow. The 01A/01 source is blue as before but since it was squeezing up at shear line inside the cove on its seating, it’s usually yellow. The head match for the 01A/01 source is 01A itself and that’s hidden behind the pale orange massif attached to 01 (visible here but not dotted pale orange).
Photo 17- this is the same as 15 and 16 with two more additions. It shows the chimney for Ma’at 03 in beige dots (tracing its centreline) and the continuation of the beige line down the 03 source bump on the body. You can now see how the 03 chimney’s curved base nested over the curved base of the bump on the body. The three beige dots on the body run upwards towards us from the base of the bump (a mini volcano, like the other bumps, through being uplifted). The three dots run up to the true rim of Babi overlooking Hapi. This is a spectacular, curved overhang over Hapi. The area under the three beige dots is deeply undercut into a cave which we can’t see here. That’s more evidence for this being a gas source for 03. And of course the smaller blue dots extend, as in photo 2, to beyond where the head rim obscures the majestic, overhanging curve. That curve neatly matches (is concentric with) the curved base of its volcano as well as the curve of its chimney base, now 1000 metres directly above.
Still with photo 17, the apparent offset of the head lobe rim to its body match here is almost entirely due to Rosetta’s viewpoint parallax but technically speaking there’s a fraction of offset due to head tip. Head tip also contributes to the head terracotta/bright green line being 4% shorter due to foreshortening. However some of that 4% may be due to the fact that the dark green/terracotta corner on the head rim was frilled upwards and backwards which is why its two yellow lines don’t progress to a joined-together point like their body match. The frill needs ironing out so that it extends out to match the green/terracotta corner on the body. Careful analysis of the mauve match shows that the second layer pinned the back of the frill down on the body while the outgassing from under the first bump (the main gull wings) frilled up the edge on that corner. Even Ma’at 01’s perimeter did some of the pinning because it’s part of the zig zag. There much about the frill in Parts 5 and 7. It extends along the head rim further than is visible here.
There’s also a suggestion of a collateral hole, supplied by the beige 03 chimney. It’s nested up under the second head layer and in line with the chimney and Ma’at 03. This suggests Ma’at 03 delaminated upwards from this larger hole so that both were once one hole, clamped over the 03 source. That would be like 01 sitting on 01A and both being clamped over their respective source.
The red lines are now running more faithfully from their true sources on the body to their respective pits on the head. Before, they were running notionally from the green-dotted bumps. The long lines across the shadow are largely dispensed with in this version. There are still short lines running up from the body sources but they’re just the rough distance of gas travel from the sources to the holes when they were seated on the body and herniating upwards. The 03 source line has three dots running down its volcano bump. They depict the gas flow, hidden on the other side and flowing out of the undercut cave. The 02 and 01A/01 sources aren’t undercut.
Photo 18 also shows the 03 gas path through the chimney more faithfully and a short offshoot to the intermediate hole tucked under the second layer rim. It also shows a tentative position for an intermediate hole along the 02 gas path. This is only because both the 01 and 03 paths have intermediate holes. Seeing as this comet is almost obsessively symmetrical when delaminating the suggested hole is annotated just as a suggestion. It’s not readily apparent as a hole but may make itself apparent as a narrow collateral dyke. There’s already a tiny collateral dyke within the yellow match line just below the suggested position and that tiny dyke has the 02 path running right under it.
Finally, the dimple just above the head rim, midway between the 02 and 03 paths is the position of the bright green dot that fits over the 02 bump in photo 15. The 02 bump is dark green here, in keeping with the others as that’s their usual colour.
This Part should be regarded as a twin to Part 52. Reading that part will give more background as would Parts 38-41. However, this part can still be read and understood in isolation. As is often stated here on the stretch blog, the process by which stretch theory explains the delamination of the pits known as Ma’at 01, 02 and 03 is described below as if it’s fact so as to spare the reader endless qualifications and conditional statements. Of course, it’s a hypothesis but after two years of scrutinising this small area (hundreds of photos for very many hours) I’m sure the evidence is highly compelling. It’s so extensive that only a small amount of that evidence can be presented in this post with the rest left to links to other posts.
The Rosetta mission is going to land the Rosetta orbiter on 67P/C-G on 30th September 2016. At that instant, all transmissions will stop and the mission will end.
On the way in to land, Rosetta will analyse the pits at Ma’at on the head lobe near the head rim. They’re named Ma’at 01, Ma’at 02 and Ma’at 03 although Ma’at 02 has recently been renamed ‘Deir El-Medina’. Rosetta is slated to land between 02 and 03. I’ll generally refer to the three pits as 01, 02, and 03 for brevity here with occasional reference to their longer names.
I’m posting this because I think the largely accepted view that the pits are probably sinkholes might affect the decisions on how to take the data on the way in to land. For instance, it might affect the decisions regarding attitude orientation (where Rosetta is pointing) and which instruments are switched on for taking data. At the time of posting this, there are intense discussions as to which instruments can be allowed to operate and to what extent because of acute power and telemetry constraints. This Rosetta blog post published recently outlines the constraints:
Of course, the mission scientists will be attempting to point the instruments into the pits so you might think the pointing issue is academic. But the pits have delaminated from each other. The knowledge of their delamination might prompt the pinpointing of certain specific areas, perhaps at the stratum of the delamination in successive pits. Or extra scrutiny of the boulders in Ma’at 02, knowing some might’ve fallen from the sides of Ma’at 03 as it delaminated.
THE FOURTH PIT AT MA’AT
There’s also a fourth pit on the head, next to the other three, that hasn’t been identified as such because doesn’t look like pit. It’s the most most important of the four because it’s the original one the other three delaminated from and today it’s just the old, scoured-looking floor with no walls. It’s lying right under the landing flight path (I believe) and data will probably be taken from above it. But surely it would be a good thing to know in advance that it’s not the comparatively boring flat expanse it seems to be, but key to everything Rosetta is analysing in the last moments of her 2-year mission.
THE LONG-AXIS DELAMINATION PROCESS
The long-axis delaminations at Babi/Hapi are presented in more detail in Part 38:
There’s additional information on the long-axis delaminations in Part 52:
Part 52 was linked in a comment I made on the “Celebrating Two Years at the Comet” post in the hope that a low flyby of the Babi slide would provide data on the jet there that’s related to the 02 source and therefore to Ma’at 02 itself. The Babi slide itself (Part 40) is beyond the scope of this post but puts it in perspective.
According to stretch theory, pits 01, 02 and 03 came about as a result of onion layers delaminating along the Babi/Hapi rim under the influence of long-axis stretching of the comet. 67P stretched into a quasi ellipsoid and continued stretching even more along the long axis of that ellipsoid. This eventually caused the diamond shape we see today that defines the body and, partially so, the head lobe. The long-axis delaminations along Babi (and Seth) were therefore trying to accommodate the stretch. Long-axis stretch is why Hapi and Sobek are longer than Bastet and Anuket, resulting in a neck with an elongated cross-section that’s aligned with the long axis of the comet. The cross-section and its long-axis alignment can be seen in Hirabayashi, M., et al 2015 extended data figure 2:
The tensile force vectors operating during the stretching process would have been brought about by spin-up via asymmetrical outgassing.
The long-axis stretch and delamination process happened when the head lobe was still attached to the body, prior to shearing. The shear line runs along the Babi/Hapi rim where the delaminations are most apparent.
Since the layers were delaminating along Babi, any particular feature on the original layer that delaminated would be reproduced in the successive delaminations. This would include the pits/holes and the uplifted mini-volcanos supplying them. There are also other features such as a an obvious trident shape. This is why the mini-volcanos in photo 4 are so similar and near to being equidistant:
Since the tensile force vector for the long-axis delaminations was in line with today’s Babi/Hapi rim and the head was still attached, it meant that the delamination layer fronts would be expected to be at 90° to that vector, or at least notionally so, all other factors being equal. However, this is notwithstanding the initial layering configuration prior to delamination and indeed this appears to make the Babi delaminations angled forward towards Bastet somewhat. This may be a primordial arrangement but it might instead be due to the pinning of layers at the proto-Anuket region, causing the V-shaped configuration we see on the head today and, rather disguised, on the body too (see Part 27, ‘Signature 3’).
However, notionally speaking, the delaminated layer fronts were ‘draped’ across the long axis tensile stress vector. Since the head was still seated on the body during long-axis stretch, these draped layers ran from proto-head to the body, across the future head lobe shear line at the Hapi rim.
THE REASON FOR HATHOR BEING FAN-SHAPED
The head lobe shear line itself runs in the long axis plane or to be more exact, in a plane that is parallel to the long-axis plane. The shear line is also the line along which the proto-head started herniating. So it was a weak spot. The head chose to herniate along, and eventually shear away from this particular line because it was literally a shear line: a sharp tensile strain gradient occurred across it causing differential strain forces. Whilst the long-axis tensile forces were the same across this line (no gradient) the differing tensile force resistance (strain resistance) of the matrix either side of the line resulted in the strain gradient. This caused shear along the Hapi border with both Babi and Seth and it’s indeed the very reason for all three regions exhibiting different morphologies. Furthermore, it’s the reason for Seth and Babi being rough mirror images of each other fanning out from the straight portion of the Hapi rim. That straight portion was where the shear force was most potent, causing the most defined head shear. At Bastet and Anuket the shear turns into a yanking-up which is why the neck looks similar at both ends (Bastet: Part 21 and Anuket: Parts 24,25).
On one side of the shear line there were the more susceptible Babi delaminations; on the other, the proto-Hathor cliff, still clamped face-down on Hapi, was delaminating more subtly: it delaminated into narrower layers (the strong striations we see today) and did so in a fan shape. This is why both Hathor and Wosret are fan-shaped.
The greater resistance to strain of the Hathor cliff matrix when seated on Hapi was presumably due to the matrix being colder and more brittle. This property would become more pronounced with the depth of Hathor under the seated head and lead to increasing strain resistance towards the central area. This translates to less stretch at depth and would be an elegant explanation for the fan shapes at Hathor and Wosret: less stretch at the bottom of the fans and more stretch at the top couldn’t help but form a fan shape.
This gradation of strain resistance with depth would also account for the apparent directing of the long axis tensile forces around the proto head lobe and the consequential sudden strain gradient at the Hapi rim where the fan-shape strain mechanism gave way to full-blown layer delamination across Babi. That would explain the location of the shear line and by extrapolation, the shape the head rim traces. Thus, the symmetrical shape of the head when you look down on it is explained (yet again, aligned with the long axis).
Moreover, the nodule sitting centrally at the base of the Hathor cliff could represent the threshold at which no stretch at all was possible (100% strain resistance). It would be like trying to stretch and deform an avocado. The flesh would stretch and deform around the unyielding stone and the brittle skin would crack. If made of several layers, the skin would delaminate as well or instead. The Hathor cliff matrix would then represent an intermediate phase of reluctant, partial stretch as would happen if the avocado stone had a thick, semi-ductile shell. For 67P, this translates to less stretch at depth with the tensile forces being directed around whatever doesn’t want to stretch or wants to stretch less.
If 67P was a perfect ellipsoid the tensile forces wouldn’t have a proto-head to get forced around and work free via shearing along Hapi and Sobek. However as soon as any proto head lump started to herniate under stretch, it could be visualised as an avocado with two stones or a peanut-shaped stone. The tensile forces would start to be directed around the girdle of the peanut, this causing shear at the surface in line with the girdle i.e. at the shear line/head rim line we see today.
This is the first mention of the Hathor fan-shape explanation on this blog as well as the fact of the shear line being an actual shear line where shear forces acted either side of it. These will of course get their own posts. They’ve been brought forward here because of their relevance to the long-axis delaminations.
The Ma’at pits were caused by outgassing, yes, but in a shorter, sharper catastrophic episode than through gentle sublimation. They never had roofs that fell in after a cavity had gently eroded away underneath. They acted just like volcano calderas and even had their uplifted mini-volcanos that supplied them with the fast-sublimating gasses emerging at the shear line during head lobe herniation. These are clearly visible on the body today, aligned 1000 metres below 01, 02 and 03. When the head was still attached, the already-delaminated pits sat on (or rather, just next to) the mini-volcanos.
Whilst the Ma’at 02 pit probably did sit on or very near its bump at the time of being supplied, the bump delaminated a little further from the outgassing source signature we see today. So it continued delaminating longways after 02 delaminated upwards. This is evidence that a small amount of long-axis delamination continued even as the two ‘zig zag’ layers were delaminating upwards under the influence of head lobe herniation.
This slight continuation of long-axis delamination after head herniation commenced is perhaps corroborated by the 03 path. 03’s outgassing source (the undercut cave) hugs its volcano very faithfully but, together, they are slightly further displaced along the body from today’s 03 pit on the head. The 03 source has the strongest 3D match to 03 itself: a bell-shaped chimney, starting at the third volcano which is seen to curve up across the first layer of the head lobe to meet 03.
So the gas source for 02 is slightly displaced from its volcano. The other two sources are hugging theirs, just to one side. This is consistent with the gases at the shear line finding their way out firstly from the shear line itself but also from under the draped ‘lasagne layer’ in the reverse direction of delamination as you’d expect.
THE EVIDENCE FOR THE VOLCANOS OUTGASSING
The mini-volcanos are what are known as the ‘gull-wings’ in this blog because the first set that was matched from body to head looked like a pair of gull wings. That was in Part 5, December 2014. The other three sets of gull wings delaminated from it, along the long axis, so they partially preserve the gull wing shape. It wasn’t known in 2014 that they had delaminated but there was much evidence of former outgassing from in front of all three sets that was noted at the time. I noted the outgassing evidence from in front of sets one and two, suggesting it was the reason for the uplift. Rosetta blog commenter, Robin Sherman, often referred to the possible ejection of material from the cave under the third set because it looked scoured-out somehow. Part 5 talks of the first set being uplifted, hence their gull wing shape. Parts 7 and 8 discuss the path the gasses took from the soon-to-be Hapi that was still trapped under the head lobe. That discussion incorporated the second set of gull wings. Hence, all three sets were identified as experiencing catastrophic outgassing and therefore being uplifted. And of course, it has to be remembered that this entire section of body had already been matched to the head rim underside anyway. That was done in Parts 1 and 2. But still, it wasn’t realised that the gull wings or volcanos were delaminated from each other. That came in Part 38:
You can click through to Parts 39-41 from Part 38 for the recommended extra background reading.
The long-axis delaminations and how they match to the head layers is explained in much more detail in Parts 38-41. Regular readers may notice that the numbering scheme for gull wings above is different from in Part 38. The numbering above is for clarity regarding the matching of mini-volcanos to Ma’at holes in this post.
THE TWO-WAY DELAMINATION (LONG AXIS VS HEAD HERNIATION)
Yellow- true strata. The body components look wiggly due to being flaccid after recoiling backwards along their length.
Red on the head- quasi strata. These are the head lobe herniation ‘strata’ which are really just passive chunks of matrix that yielded to head lobe herniation. They just happened to yield to that upward tensile stress at a ~50-metre depth, tore from the shear line and recoiled up the head lobe. In so doing they hid the real strata within them (see below). The two upper red lines are the layers that recoiled. The third bottom one is the head rim. The top red line is the one at which the true head lobe strata (yellow) appear to stop dead. In fact, the head strata carry on within and across the red quasi strata but are almost hidden except in the head cove. Red and yellow can be seen cross-cutting in the cove. The uppermost red line hasn’t been discussed so far in this part because it was the very top head herniation layer and it slid up past the Ma’at holes (Ma’at 02 is dotted blue, just below this line). The layers above the first (rim) line and second line are the two that we’ve been discussing and which have the zig zag at their ends. The uppermost line appears to have been set back from the shear line when on the body which is why there’s a blue dot on the body. That’s the Ma’at 02 body delamination. So the head took the bottom two layers of the Ma’at pits that sat on their Ma’at sources. And the body kept the very top layer. That blue dot on the body (or rather its surrounding walls) sat on top of where Ma’at 02 is today.
Red on the body- these are quasi-strata as well. The same principle applies as for the lines for the red quasi strata on the head but the signature of the layers is less obvious. The red lines on the body were originally joined to the lines on the head: bottom body to top red; top body to bottom head; and middle to middle.
Blue- top blue is Ma’at 02; middle is the 02 source; bottom, on the body, is the jet that originally sat on top of Ma’at 02. Its adjacent red line wrapped round it and clamped to the red line above Ma’at 02 when they were sitting on their common 02 source at the shear line.
The two-way delamination explains the paradoxical, different-angled ‘strata’ in this location at eastern Ma’at. They delaminated in two directions: along the long-axis stretch vector and along the upwards head herniation vector. They’re at a notional 90° angle to each other as mentioned above. That’s the best way to visualise it close-up. From a distance it’s a bit more nuanced.
The two-way delamination is the reason the strata appear to cross-cut inside the head lobe ‘cove’ above the border between Seth and Babi. And it’s why head strata appear to stop dead in their tracks at a straight line running all the way from western Ma’at, through the cove, and on round to Bastet in the east. That impressive line is the upper layer of the head herniation delaminations. These delaminations could be viewed as sliding or even recoiling upwards after having torn at the shear line due to the herniating head pulling on them.
Together, they form that impressive green zig zag at their ends (photo 8). The zig zag betrays the delamination. But these two upward herniation layers are not real strata. They’re just layers of passive comet matrix which were torn at the shear line by head lobe herniation and recoiled (Part 41). They just happened to fail at that particular ~50-metre thickness, one after the other, as the herniation progressed. But the most important thing to remember is that both upward-recoiled layers contain all four true strata that originally delaminated along the long axis before tearing right across their width at the shear line and recoiling upwards. Those are the true strata and they supplied all the material for the two upward-recoiling layers which appear in photo 22 as quasi-strata. The quasi strata almost completely hide the true, long-axis-delaminated strata. The true strata became almost totally hidden due to tearing across their widths, succumbing to the quasi strata’s 50-metre-thickness requirement and becoming flaccid as they recoiled up the head and along their length.
But these hidden, true strata are traced in Part 41. And most crucial of all for this post, the true strata are the long-axis-delaminated layers that contain the delaminated holes, Ma’at 01, Ma’at 02 and Ma’at 03.
I hope the mission scientists can take this into consideration in their deliberations on how to take the pit data as Rosetta descends to the surface on 30th September 2016.
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
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All dotted annotations by A. Cooper.
Copyright: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA/A.COOPER