Part 54- Atum Crust Slide Away From the Shear Line. 

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

The header photo is reproduced below with its key. The dots are degrading this image in photos 1-3 for some reason. The original is placed below in all cases and has lost none of its clarity. It’s best to ‘fly solo’ anyway once the dots have told you where to look. Photos 5/6 are unaffected. 


The Anubis/Atum crust slide vectors have been worked out incrementally over time. The term Anubis/Atum was really coined for this one very obvious facet of the diamond-shaped body lobe. This was before Khonsu was added as a named region when it emerged from the winter shadows. Hence the existing page in the menu bar regarding stretch in this area still includes “Anubis/Atum” in the title that largely deals with Khonsu. 

This post shows additional crust slide vectors for southern Atum. It’s telling that the crust slide is in the exact opposite direction from the direction of head lobe rise from the shear line. This is consistent with the behaviour along the entire length of the shear line from this point to Seth, Babi, Aker and Anhur (Parts 26, 32, 35, 40 and the Paleo Rotation Plane Adjustment page). Aker’s slide is not posted yet. 

There will be more explanation and additional, adjacent slides added later in this post and/or a later post. Those slide vectors (and stretch/delamination vectors for Khonsu) complement this particular slide very well and as usual show a tendency to follow the tensile force vectors of stretch. The Khonsu delamination is on the “Anubis/Atum” page already. 


Header reproduced


The keys are narrative keys as is often the case but they are shorter in this post. Some colours are divided into paragraphs but are still part of the key. 

Fuchsia lines- these two wavy lines are the main crust slide match. The upper line is the seating and the lower line is the slid crust that was originally clamped at the seating. The arrows below the bottom line are sitting on the slid crust and show its direction of slide. The arrows above the top line don’t sit on slid crust but are placed where the head rim once sat before it sheared from the body. They show the direction of travel of the head as it rose on the stretching neck. 

The upper fuchsia line is therefore contiguous with the shear line where the head lobe rim once sat. This match for the head lobe seating was presented in Part 17. The Part 17 header is reproduced below to clarify this. It’s of course the reason that this particular crust slide started from this upper fuchsia line- it’s the recoil effect, just like all the other crust slides around the shear line (not only on the body but the head too). 

It should be borne in mind that the upper fuchsia line represents the continuation of the shear line. The shear line/head rim match has been traditionally denoted in red for this side of the comet ever since Part 17 so in this photo, the red-dotted shear line meanders down from top-left, turns sharp right and soon joins this upper fuchsia line. From that point on, the shear line and the fuchsia seating line for the crust slide become contiguous, all the way to the right hand side. 

So the head sat above and to the right of this red/fuchsia line, the head rim’s shear line, and the area both below and to the left of it did not have the head lobe sitting on it. But that area did experience crust slides away from the line. This part is dwelling mainly on the downward fuchsia slide in the header, that is, the slide from along the bottom of the depicted head rim seating. The crust slide from the section to the side will also be shown below but not described in detail. 

Red- the traditional shear line as described above. It should be considered as continuing contiguously with the upper fuchsia line, as also described above. It may look a bit weird as a quasi square when the head rim is fairly straight all round. This is for three reasons. Firstly, it’s a close-up. Secondly, the shadow on the right enhances the squareness. Thirdly, this is the most marked step-down in the head rim on the whole head lobe. The red shear line does a sharp left just off frame at the top and runs along the top of the frame just outside it. This will become clearer when the Part 17 header is shown below. 

Fuchsia dot pairs- these larger fuchsia dots show a matching feature of two adjoining dips. They’ve slid in the same manner and the same distance as the nearby main slide. Notice however, that the slide direction is slightly to the left and that there’s a small lateral gap where there are no matches. The gap signifies a lateral rift which is further evidenced by the highly curved lines between the main fuchsia-dotted crust and its seating. The subtle leftward slide vector for the fuchsia-dotted pair is the very beginnings of the influence of the stretch vector directed towards the long axis tip at Apis (see the Anubis/Atum page). Apis is ~1.5km leftward in this view. 

Yellow- three dips that match from the top line (shear line) to the slid crust (their apparent bled shadows left behind just before the slid crust stopped). 

Small red dots- wavy lines that connect the three yellow features.

Photo 2- this shows the other slide away from the left side of the head rim line.

Fuchsia chunk at left with slide arrows the bright green feature- this is actually just the seating area of the crust which was attached to this part of the shear line and that has now slid in the direction of the three arrows to a point that’s somewhat off-frame, not far off. This chunk will be seen in the zoomed-out overview below. The bright green feature is a mini match to the slid chunk which will help you fit it back when you see the same feature on the chunk. Fuchsia is used again for the crust chunk perimeter because it’s the traditional colour for Anubis. Notice that it’s been drawn as being exactly contiguous with the red shear line because it too tore away from the head rim. 

Photo 3- as photo 2 but with some extra annotations. 

Photo 4- the Part 17 header.

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

Red- the head rim at top and the shear line below which match as described fully in Part 17. 

‘H’- This shows the area where the head sat in the above photos and of course the actual corresponding section of head that has now risen on the stretching neck to a point one kilometre above.

Photo 5- the overview. This was done some time ago so the colours are different. It may get updated so that the colours are consistent with those above. 

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

Yellow- slide vectors. 

Red- the shear line plus the slid crust that was fuchsia above (at bottom right). The slid crust perimeter may follow a slightly different line due to much lower res than the header. But it is close. Also the red line for the head rim seating/fuchsia crust seating isn’t as wavy as the fuchsia seating line in the header. This is only partially due to the lower res but also a higher perspective. The curves of the fuchsia seating in the header are partially stamped on the cliff, a fraction below the red line in this view. 

Fuchsia- chunk plus seating. Notice how the long yellow slide line links the chunk described above to its seating which was all that was shown above. This includes the bright green mini match. 

Dark green- the lower line is the southern rim of the green anchor (Part 24) and the upper one is the chunk that was pulled out of the green anchor tray as the neck stretched. The two dark green wavy lines match because the southern end of the chunk sat on he southern rim of the anchor tray. The yellow line is of course the slide track which was probably more like a ‘transportation within the neck matrix’ track. 

The green chunk is actually just a very big chunk sitting within the green ‘tell-tale line’ that links the green anchor to its head lobe match on the head rim. There are four such tell tale lines. They’re long, fine delaminations running up the neck at Anuket. The delaminations were fine shards, pulled from the shear line crust and dragged up the stretching neck within its matrix. The chunk is the biggest lump, not a fine shard. 

As for the green chunk, thrown in casually here because it happens to be part of an old annotation, it’s the site of one of many spectacular finds by Marco Parigi who has investigated the evolving neck area. He’s found several changes there, either side of perihelion 2015. In other words, these are changes over the last two years or less. Here’s his blog post on the cliff collapse at this green anchor chunk:


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

To view a copy of this licence please visit:

All dotted annotations by A. Cooper. 


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