67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 40

THE 800-METRE RADIAL LANDSLIDE AT BABI 
   

Key

4 Fuchsia dots- these denote each of four cuboid lumps that slid across Babi from the gull wings.

Small fuchsia- perimeter of the front faces of the cuboids.

Red- slide direction which is consistent with the centrifugal force vector. It emanates from near the north pole. 

Yellow- many bunched-up mini onion layers are to be found between these yellow lines. They look like shards of thin slate that have been stacked in a sloping pile, each layer peeping out from the one above. They were once spread out over Babi towards the gull wings at the shear line and formed what was ostensibly one main onion layer, the top layer of cometary crust (‘level 1′ in Part 39). They contribute to the bunched-up bulk behind the two middle cuboids’ faces. Each yellow line rises up quite a steep slope of material, which is part of the reason for their being at an angle to the red lines. These are real lines (see unannotated version). They appear to be linked to each cuboid vertex and each set of gull wings (via the red lines which are also real lines in the unannotated version).

Green- the five sets of delaminated gull wings.

Dark blue- the north pole.

Brown- the paleo pole adjustment (Part 37).

Orange- the perimeter of the Aten depression. The bottom edges of the four fuchsia cuboids join in one remarkably straight line and this line completes the perimeter of Aten. 

/////

The ESA regions map is at the end of this post (photo 10). All references to up, down, left, right are in the ‘upright duck’ view with the head lobe above the body lobe, unless otherwise stated. Longer photo keys are concluded with ‘/////’.

INTRODUCTION

This part builds on the material presented in Parts 37 and 38. It may be difficult to see how this sliding of the Babi crust layer happened without reading those parts. However, the essence of the arguments laid out in those posts is as follows. 

The gull wings delaminated along the long axis stretch vector, which is in line with the Hapi border and the Hapi border is the shear line where the head lobe sheared from the body lobe. The delamination was therefore towards Aker at the comet’s long axis extremity. This is the main stretch vector as dominated by the comet’s core and evidenced by the fact that the body is nearly a perfect diamond shape. You can click the second video in this Rosetta blog link to see the diamond shape as viewed from below Imhotep:

http://blogs.esa.int/rosetta/2015/09/29/an-update-on-comet-67pc-gs-water-ice-cycle/

The stretched long axis of the diamond had to involve the core. Core material was stolen from the short axis and given to the long axis during stretch. The crust at Babi had to yield and succumb to that long axis direction of stretch. It was too brittle to stretch so it delaminated in that direction. You could call that a preliminary landslide but it’s in the long axis direction along the Hapi shear line which is itself directed along the long axis. And it was probably more of a prising apart of layers than a slide. The landslide in this post involves the same section of Babi crust but now that it was much more loosened by the initial long axis stretch, it was able to slide radially. That radial slide was in sympathy with the centrifugal force of the fast (circa 2-hour) comet rotation. 

The centrifugal force wasn’t enough for this crust near the north pole to escape but the next best thing was for it to slide to a higher radius. That radius was at a point where it could conserve angular momentum and the slide would be in a line directly away from the north pole. It would explain why all four of the cuboid lumps ended up with their bottom edges in a straight line overhanging Aten. That was the desired radius from the rotation axis for AM conservation.

The initial delamination along the long axis was in banded layers that were delaminating like the blades of a Venetian blind. Those delaminated layers ended up as four bands across Babi running lengthwise from Hapi to Aten. They delaminated in the direction of Aker at the comet’s long axis extremity. Those four bands correspond roughly to the five red lines in the header (five lines needed to enclose four bands). However the red lines are really the slide vector and the actual bands were at the angle which is now preserved in the yellow lines. The gull wings were simply slightly more recognisable features at the ends of each delaminated band, spread along the shear line. They are more recognisable due to being pushed into a double lump (gull wing) by slurry emerging at the shear line prior to delaminating into 5 sets. The slurry emergence was described in Part 7.

Notice that the left hand red line doesn’t emanate from a gull wing set and, by the same token, the right hand red line emanates from the second set not the first. This means that instead of it being a perfectly tidy scenario of five gull wing sets enclosing four delaminated layers and their eventual cuboids, we have four sets (2,3,4 and 5) enclosing three of the delaminated layers/cuboids and a fourth layer/cuboid on the outside of the fifth gull wing set. So that left hand layer/cuboid was pulled or ‘delaminated out’ between the fifth gull wing set and Aker. There’s some evidence that there’s a sixth set of vestigial gull wings at Aker anyway but that’s not certain. It’s besides the point though because you don’t need gull wings to prove a delamination. The left hand cuboid, being of the same character as the first three shows that this last section between set 5 and Aker did indeed delaminate. Also the surface of Babi has the same characteristic look all the way to Aker, suggesting the same delaminating process was at play across the whole swathe of Babi. 

As for the gap between the first two gull wing sets which don’t have an accompanying cuboid, that’s because it appears not to have been a delamination (layers sliding like the card deck) but a straight tear and rifting apart. 

Once these delaminated crustal layers were loosened by that long axis slide towards Aker, they slid radially along the direction of the red lines. 

The cuboid faces slid from their former positions between the sets of gull wings. Each section slid along and between the red lines, preserving something of its original form. And each section scooped up its own delaminated band as it slid across Babi. Or rather than scooping, it slid across the top of the mini layers (‘shards of slate’) within that band and by the time they all reached Aten they were bunched together in a cuboid that was about three times the thickness of the original layer. That’s because the cuboid areas are roughly a third of the area of the delaminated ‘Venetian’ bands. What are now the faces of the cuboids overhanging Aten used to be between the gull wings and they stayed on top all the way along the slide. In fact the faces eventually overtook the layers below them which are today spread back across Babi in a slope behind the faces. The yellow lines run down that slope and stop at the bottom. 

Each yellow line preserves a vestigial signature of the original gull wing delamination (see unannotated versions of the header and of photos 7 and 8). That signature is in the form of larger chunks stepping up slightly more markedly than the thinner shards and doing so in a line from top to bottom of the slope. That causes a visible line running up the slope of shards to each cuboid vertex. The line is probably not just a signature the original gull wing signature but a signature of the edge of the entire ‘Venetian’ band. The bands delaminated along the long axis towards Aker. Only then did they slide out to Aten and bunch up along their length in the process. They bunched up into the sloping shards which were now a third of the length of the original band. Therefore the Venetian layer edges also bunched up to a third of their original length but still managed to remain as a step (the yellow lines) because they were of course stepped when originally delaminated as bands across Babi towards Aker. 

The slope of shards that’s bounded by the yellow lines consists of very fine mini delaminations of what was ostensibly a single top onion layer. That would be the ‘level 1’ onion layer as described in Part 39. The mini delaminations, being so numerous, might have facilitated the slide just like the analogy of the card deck sliding across the croupier’s table. They’re more evident in photo 8.

Photo 2- side view 

   

In photo 2, the left hand red line is omitted. Also, the dark blue and brown dots for the north pole are hovering just above their actual positions in Hapi behind the rim of the shear line. All other colours are as for the header photo.

Photo 3- underside view. 

   

Photo 3 is a four-frame composite NAVCAM image. The top left frame shows the left hand three cuboid faces and the beginning of the fourth, right hand one (you can see its dot chopped in half). The top right frame shows the whole of that right hand cuboid face and a bit of the next one to its left. Aten is outlined in orange on all four frames so as to build up an impression of its extent. 

You can see from this photo that the four cuboid lumps are very distinct, protruding much further out over the Aten depression than the rest of the Aten perimeter. This is because they all slid to a radius above the rotation axis that allowed them to conserve angular momentum. That radius was irrespective of the Aten perimeter. They overshot the perimeter and that is why they look alien to the rest of Aten. 

An OSIRIS photo shows the base of the cuboids inside the Aten depression to have an obvious crack running along the bottom. This lends weight to the idea that they were dumped there and aren’t really integral or native to the Aten perimeter. This side of the four cuboids that drops down into Aten is known as the ‘cliffs of Aten’ which is a recognition of their spectacularly tall and blocky morphology. 

THE ATEN DEPRESSION AND THE CUSP BETWEEN SLIDE AND ESCAPE.

OSIRIS scientists have puzzled over how the Aten depression came about, specifically how it could have lost its 0.1km cubed of material via sublimation alone. Explosive ejection of material has even been suggested (via pressurised pockets of gas). In other words, they wonder why it’s so deep. One reason it appears so deep is that one side has been built up by the four cuboid lumps that slid from Babi to above the original Aten rim. They should really be called the cliffs of Babi. The base of the cliffs is where the genuine, original Aten depression starts. 

And the original, shallower Aten ‘depression’ is of course very likely the crater left by a missing slab. That’s because it extends along exactly one side of the stretched diamond and is diametrically opposite the Anubis slab that also takes up exactly one side of the diamond. 

Why else would two diamond sides exhibit elongated craters that take up the exact length of a side? It’s consistent with the tangential, sliding departure of the slabs and not consistent with random sublimation- even when, rotation, obliquity and solar irradiance is invoked. Slabs sliding away from any one of the four sides will simply make that side more distinct. But no daily or seasonal irradiance pattern can explain the huge loss of material from exactly two diamond sides (Aten and Anubis) while leaving the diamond side between them completely intact and free of material loss (Ash).

The loss of the Aten slab may well have instigated the Babi landslide by leaving the delaminated layers unrestrained along their Aten edges. The Aten border is likely a signature of a threshold. It’s the cusp between a radius of rotation that induced a tangential escape velocity and a radius that would only allow radial slide. Anything above that radius would escape (tensile adhesion failure permitting). Anything that was sliding radially outwards from below that radius of rotation couldn’t slide beyond that cusp. The four cuboids therefore stopped at the Aten border and beyond the border, the Aten slab escaped. This is simplistic though because the radius of rotation varies along the Aten border. However, it becomes workable when bulk sections of crust, or massifs, such as the four cuboids are sliding about while clamped together. They would be sharing the above average and below average components of the tangential velocities. The same applies to the Aten and Anubis slabs.

The escape/slide cusp would also explain why all the mini delaminations in the four bands bunched up in such a well-behaved manner at the Aten border after their radial slide: those that were already at the Aten border didn’t need to slide further out because they were in equilibrium. Those layers a little way towards the gull wings (lower radius of rotation) needed just a small adjustment so they slid out and over the outermost layers to sit directly on top of them at the border too. Those layers that were at a still lower radius slid to the same Aten border cusp and ended up on top of the growing pile. Finally, the faces of the cuboids, originally sited between the gull wings slid the furthest but to the same Aten cusp. Adding in some discrepancies in friction between layers due to the lessening weight of upper layers and you have the overshooting of the faces and sloping yellow lines of deeper layers trailing behind them. There was probably some yanking too of the material at a lower radius between the gull wings by the material at a higher radius (see the ‘pie-shaped crust effect’ sub-heading in Part 34).

MORE VIEWS OF THE CUBOID SLIDE

Photo 4- this is photo 3 with extra head annotations.  

 

Extra annotations on the head lobe in photo 4:

Yellow- the cove (Part 35) which constitutes part of the head rim shear line.

Terracotta- the rest of the head rim shear line that’s visible.

Dark green- the sites on the head rim underside where the third, fourth and fifth sets of gull wings on the body kissed. The third set is on the right, fifth on the left. The third set is the classic set that matches head cove to body. That is, the third set on the head was matched to the identically shaped third set on the body. This was done both in plan view and side view (Part 5).

Light blue- these are four subtle ridges on the head that correspond to the left hand three cuboids. In other words, those three cuboids used to be joined to these four lines (four lines enclose three interstices). So each cuboid was attached to each head interstice when it was still a delaminated ‘Venetian’ band spread across Babi. And of course, that would have been when the head was seated on the body. 

Since the cuboid faces are said to be the topmost layer that stayed on top all the way through the slide from the gull wings to Aten, it follows that the faces we see today, teetering over Aten, used to be attached to the head interstices. That is consistent with the fact that both the cuboid faces and the head lobe surface between the interstices are the same lighter colour.

/////

The right hand cuboid appears to be related to a now-eradicated signature in the cove. That’s because its slide track is to the right of the third or classic gull wing set which defines the left tip of the cove. 

The four subtle head ridges are more pronounced under certain lighting. Their extent up the head corresponds to the cove delamination height (the fourth yellow curve in photo 6, below). There’s a sloping line that’s common to the top of the third and topmost cove scallop and to the top ends of these subtle, light blue ridges. That line is a head lobe crust recoil behaving in mirror fashion to all the radial body crust recoils we’ve seen from Parts 32 to 40. The recoil line is responsible for the cove delamination itself (Part 35). It will get an airing in due course. 

Photo 5- another view of the slid cuboids. It has the same key as for photos above.  

   

Photo 5 shows that the middle two cuboids don’t have uniform straight faces as they appear to have in other photos. They are kinked with the upper portion facing somewhat upwards in this view. Their two respective dots have been placed on these two slightly angled sub-facets. The lower facet counterparts on each of these two middle cuboids seem to be the same ‘height’ as the two smaller, flanking cuboids. That’s because all four seem to share a common ridge that runs across the tops of the flanking ones but halfway through the middle two. But this isn’t at all apparent in other photos. 

Photo 6- this is the same as photo 5 but with extra head lobe annotations.  

 

The head lobe dot colours are as for photo 4 but with a small difference. The cove shows all three cove scallops (four ribs enclosing three scallops). 

Photo 7- the overshoots (light pinky orange). 

   

Red- just the outside two slide vectors are shown.

Pinky orange- these are overhangs. In Part 39 (and above) it was suggested that if the delaminated layers that had spread across Babi then slid radially, a signature of that radial slide would be that the topmost layers might overshoot the rest of the sliding layers beneath them. This can be seen in photo 7 with each overhang pointing out along the slide vector from the north pole. The description of this phenomenon in Part 39 used the stack of cards analogy. The stack is first spread across the ‘table’ along the comet’s long axis but since there are a lot of cards (mini layers) they are still quite bunched up despite the long spread. That leaves the spread stack open to further delamination in another direction. The whole stack then slides out radially and the topmost cards slide that much further (delamination in the radial direction resulting in overshoot for the very top cards). The pinky orange protrusions didn’t just carry on and on sliding because they were travelling upwards in the gravity field to their preferred equilibrium point. They were behaving just like the cuboids they’re sitting on, stopping at the Aten ‘escape cusp’ but overshooting the rim slightly due to less weight and commensurately less friction. 

/////

Photo 8- a similar view to photo 7 (this is the previous NAVCAM photo taken on that orbit). This is presented simply as an overview of all we’ve covered here but with a slightly different viewing angle and different lighting. 

   

Photo 8 shows the mini delaminations between the yellow lines in more detail. It also shows how the two outside cuboids slid further and symmetrically from their initial positions and yet still managed to stop along the same straight line as the middle two cuboids. This is potentially the signature of all four cuboids reaching AM equilibrium at this radius from the rotation axis- or rather, these radii because they all started and finished along a line of slightly different radii. 

CONCLUSION

This part concludes the major radial crust-sliding vectors across Seth and Babi around the north pole. They encompass an angle of about 120°.

Photo 9- the radial vectors at Babi and Seth.  

 

Large brown- the paleo pole adjustment.

Brown dotted line- the paleo y axis (sitting below the paleo long axis- see Part 39).

There will be other posts on radial vectors, for example, looking at the Site A delaminations in the same detail as in this post. But the general direction of the Site A radial slide vector has already been established with the two vectors at either end (sink hole delamination and monolithic slide) and the Ash recoil behind it. 

Photo 10- ESA regions map. 

 

UPDATE 13th February 2016

Photo 11 shows the yellow lines sloping up the delaminated pile that constitutes the bulk of material sitting behind the two middle cuboids.  

   

The cuboids’ faces are out of sight, over the horizon at the far end of the yellow lines. However, the first cuboid (fuchsia dot) that slid from between sets 2 and 3 of the gull wings is very visible as is the red ridge that denotes its slide vector. 

The visible gull wings (green) are the classic set (set 3) in the foreground and the left ‘wing’ of set 4 behind that. Set four is really just a double hump and not very visible even as the single, left hand half of the hump in this view. But it’s obvious as a hump in photo 2.

The yellow lines show the distinctive change in the delaminated layers. Each line denotes a step-down as we move across the delaminated debris field (or step-up if moving the opposite way). Each step-down corresponds to a cuboid vertex at the far end of the yellow lines and a gull wing set in the foreground (three step-downs enclosing the middle two cuboids). 

The gull wing sets don’t attach directly to the yellow lines but do so via the red slide vector lines in the header photo. Those red lines aren’t shown here because they’re too foreshortened to be ascertained. 

Even the exact path of the yellow lines is open to some interpretation due to foreshortening but they are undeniably there as evidenced by the unannotated version and the header photo (unannotated version as well). 

The fact that the yellow lines are related to the cuboids at one end and gull wings at the other shows that they retain the stepped down signature of the delaminated bands from which they are derived. That’s because each band once extended lengthwise from Hapi to Aten and the four bands delaminated like Venetian slats towards Aten. On sliding radially, the bands were scooped up along their length into the bulky pile we see here behind the cuboid faces. Each individual band (Venetian slat) was originally stepped up from the delaminated band below it and that’s why today’s bulky pile retains the stepped-up signature along its length, as depicted by the yellow lines. 

Photos 12/13 are very similar. Photo 13 is actually photo 11, reproduced. Photo 12 is a very subtly different view and is slightly clearer. It’s a shame it’s cut off on the right hand side but if you toggle between the two you can see that the stacked up pile behind the two middle cuboids is all there. Photo 12 shows up both the mini delaminations and the step-ups on the slope better than photo 11/13. However, photo 11/13 shows the step-ups along the top of the slope in better relief. 

photos 12/13

   

UDATE 8th April 2016

OSIRIS VIEW OF THE BABI CUBOIDS: 

   
Yellow- visible slide tracks

Red- Part 1 matches

UPDATE 20th May 2016

This update concerns the 4th cuboid matches and slide.

Matches with slide track (red). Note the track is different from the April update above:

Without slide track:

Original:

Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA/A.COOPER

(A further update was cut from here due to realisation that the dots were badly placed and the photo wasn’t therefore very useful).

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.

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One thought on “67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 40

  1. Pingback: Part 73- The 4.5-Kilometre-Long Rift From The Northern Long-Axis Tensile Force Line | 67P/Churyumov-Gerasimenko- A Single Body That's Been Stretched

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