67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 23

MISSING SLAB E- ANUBIS
(This is the second section in a sub series building evidence for the head lobe stretching prior to shearing from the body). 

 

Key- the perimeter of the area where the Anubis missing slab once sat. It includes the Atum region as well. The bottom perimeter is in shadow. 

INTRODUCTION

The Anubis missing slab has been mentioned a few times before and it deserves a post of its own. It should perhaps be called the Anubis/Atum slab because the rough terrain of its signature extends over the Atum region too. However, all the photographic evidence for the slab perimeter matches is along the top of Anubis so the focus has been on that region thus far. Also ‘Anubis’ was coined when these perimeter matches were first coming into view across the terminator from their winter obscurity. Atum wasn’t getting as much attention in terms of released NAVCAM pictures as it emerged too. So the ‘Anubis missing slab’ is the name that’s stuck, often shortened here to ‘the Anubis slab’.

The morphology of the crater, or tray, left behind by the Anubis slab is intimately related to the gradual building up of evidence for head lobe stretch prior to shearing from the body. This is the second section of the sub series of posts presenting that evidence. As with the slab A extension in Part 22, the Anubis slab is interesting in its own right but for the purposes of the sub series, and the head lobe stretch evidence, the upper perimeter is what’s important. There will be more discussion about that at the end of this post. The following is largely culled from the second half of Part 17 along with substantial additions and some minor corrections due to a better understanding of the head-body matches in this area. It was included in Part 17 because the Anubis slab signature was revealed by the 3D nature of the matches in that post. 

THE TRIANGULAR PROTRUSIONS

This post also contains a brief recap of the triangular protrusions which will be elaborated on at length later in the sub series. The part 17 header photo is reproduced below with the triangular protrusions annotated. There’s the main one on the head rim and there are two more, directly below the main one. They’re sticking out of the neck and similarly triangular in shape. There are a few more stunted ones below that. The other colours in the photo relate to the Anubis missing slab. 

PHOTO 2 

 

Red- main head lobe to body lobe match as described in Part 17. This was discussed at length in that post, including discussion on how it refutes contact binary theory and ‘single eroded body’ theory. None of that has been copied over here. The match speaks for itself. 

Yellow- tips of the three most obvious triangular protrusions. The more stunted ones extend below these three (not annotated due to risk of obscuring them).

Bright green- body protrusions (see below).

Orange- probable body ‘protrusion’ that has completely drooped over flat.

Dark green- two dots, one on the head lobe and one on the body that matched when the head was seated on the body. The particular significance of this specific point is discussed below.

Mauve- a 3-dimensional depth match. This sits just in front of both red lines. It will be reproduced in photo 3 and discussed further in the light of the arguments presented below. 

Viewed together, the triangular head and neck protrusions look as if they used to be pressed together like the layers in a wafer or perhaps a compressed concertina. When the neck stretched, they were pulled apart but in line with each other just like the folds of the opening concertina.
It would be tempting to match the triangular head protrusions to that obvious right-hand protrusion on the body, marked with bright green dots. They would have been seated near to this point when compressed together but somewhat behind it, not right on it. The exact match point will be shown in a dedicated sub series post on these last few matches round the shear line. 

THE ANUBIS MISSING SLAB SIGNATURE

The bright green body protrusion and those to the left of it mark the boundary of Anubis. They also bear the hallmarks of being the matches to the edge of the long-departed Anubis slab (see Part 9 for the mechanism of departure for slabs A and B, which would apply here too). This would explain the wholly different morphology of the Anubis region and the different morphology is certainly the reason for it being delineated by ESA as a separate region and named ‘Anubis’.

The height of these bright green body protrusions (about 50 metres) would correspond to the depth of the slab. It’s where the slab would have torn away from the body and so these protrusions are now drooping over under the force of gravity, just like large portions of the Slab A crater rim are currently drooping outwards where missing slab A tore away. The orange, dotted line marks one probable protrusion that has drooped over completely and is now lying flat against the surface. Similar drooping overhangs are noted in Thomas et al (January 2015) and are put down to the influence of gravity overcoming the tensile resistance of the cometary material. Indeed, they use this as a means of estimating the tensile resistance. The edge of the Anubis missing slab would probably have taken on the imprint of these body protrusions.

This indicates that there was a lot of upheaval along this top perimeter of Anubis. The body protrusions appear to have resisted detachment along with the slab because they are the resilient rims of craters. They’re also sited just beyond the sudden, 90° turn in the body surface topography between Anubis and the Seth region, above, on the back of the body. 

Some eagle-eyed readers may have spotted that the red match line on the head lobe is actually following a ridge with a constant depth (around 50 metres) like a rebated rim and yet it appears to match just a one-dimensional red line on the body that starts just to the right of the dark green dot. 

One would expect it to match to a corresponding 50-metre-wide shelf on the body, not a line. However, a large part of that rebated rim was attached to the edge of the Anubis slab. So the actual slab edge itself is the shelf we’re looking for but that’s now departed. This explains why the two-dimensional surface of the rebate underside can only find a one-dimensional line to follow on the body. The section of head rim rebate that was attached to the slab edge is the section running to the right of the dark green dot in photo 2. The section of head rim to the left of the dark green dot was attached directly to the body as it rounds the bend behind the (bright) green protrusion. This part of the body is, of course, the section to the left of the dark green dot because that matches the dark green dot on the head lobe rim above. 

The matching dark green dots are, by definition, on the shear line. When seated together, they marked a unique, three-way join between head lobe, undisturbed body lobe and the Anubis slab. (The undisturbed part of the body is the long, red triangle of untrammelled craters mentioned in Part 22). This three-way junction is highly significant for the sub series evidence leading up to proof of the head stretching before it sheared. The junction and the red triangle are reproduced further below in photo 4.

The presence of the junction marks the dividing line between the seating of the right hand portion of head rim rebate to the Anubis slab and the seating of the left hand portion straight down onto the body. This makes sense because the left hand section includes the triangular protrusion that’s integral to the head rebate and its seating position has already been noted above as being on the body. 

The angle of the head rebate is correct for it to have been married to the edge of the Anubis missing slab. If we focus on the section to the right of the dark green dot, it’s angled inwards at 90° to the surface of the head lobe and, for that matter, to the surface of Anubis on the body as well, if the head lobe was reseated. The edge of the slab, when originally clamped to the body, would have been at this angle too if the bright green body protrusions are anything to go by. In other words, this section of rebated head rim is just another version of the body protrusions and when the head was seated on the body, the rebate would have continued straight on from its body protrusion counterparts. Together, they would have formed the vertical edge of the tray that contained the Anubis slab. 

The intimate fitting of rim to slab is all the more credible because of the flagging up of a paradox and its solution: the left hand section of head rim rebate that bends round to the yellow-dotted triangle and seats to the body does so in the ‘horizontal’ with respect to the body lobe. But we just said the head rim rebate was forming the ‘vertical’ edge of the Anubis tray and suddenly the same rim achieves a horizontal match to the body only 100 metres or so further on. This paradox can be resolved by the fact that the body turns that sharp 90° at the top perimeter of Anubis. Thus the affinity of the 50-metre head rim rebate in a complex 3D relationship with the top and side of the body is what betrays the signature of the missing Anubis slab. It fits firmly down on the top where the yellow-dotted triangular protrusion was seated down but would overhang all the way along Anubis to the right of the dark green dot. The overhang is the match to the edge of the missing Anubis slab. 

The width of both the rebated head rim and all the body protrusions is the same, about 50 metres. These are two different sets of features that point strongly to the missing Anubis slab being 50 metres thick. So the expected 50-metre-wide shelf on the body that’s supposed to match the head rebate was indeed there. It was the edge the now-departed Anubis slab.

That one-dimensional red line in the header photo, constituting the body match, would therefore correspond to the bottom of the edge of the Anubis slab just before it lifted off. It also means that the red line on the head lobe should really be matched to the top edge of the missing slab and not the red body line. But the slab is long gone so the body line was used as a proxy for convenience. The true match to the red body line is in fact the inner edge of the rebated head rim, that is, the line in the shadows that’s running parallel to the outer edge of the rebate. This shadowed, inner edge is annotated in the next photo. It’s a testament to the faithfulness of the matches that the outer edge of the rebate could be used as a proxy for the inner edge and yet still match to the body line so dramatically. In reality, if you seated the head back down onto the body, the red dotted line on the head in photo 2 would be hovering 50 metres above the body’s dotted line, twisting and turning along the entire length of that faithful match. Together, they would define both the perimeter line and the thickness of the Anubis slab.

Put another way, the head rim rebate to the right of the dark green dot gives it away: its flat underside, as we see it today, is itself the imprint of the edge of the Anubis slab.

The following photo with a rather alarming array of colours is included as an attempt to explain the above. It’s taken from a slightly different angle from that in photo 2 and shows up the head lobe’s rebated rim more favourably. It doesn’t extend to the extremities of the Anubis slab but it does depict the crucial area of horizontal-to-vertical matches described above.

PHOTO 3 

 

Red- shows the inner and outer rims of the head rebate and their corresponding paths when the head was seated on the body. The bottom body line is the same as it is in photo 2 and corresponds to the inner head rim line, the one in the shadows. This line traces the bottom edge of the Anubis slab. The upper body line corresponds to the outer edge of the head rim and is therefore floating in ‘mid air’ and faithfully following the line of its lower counterpart. It traces the upper edge of the missing Anubis slab. The red lines on the body aren’t extended to the left of the dark green dot to show the ‘horizontal’ part of the the head rim seating.

Dark green- when these two dots were seated together, they marked the three-way junction between head, undisturbed body and the Anubis slab. The portion of head rim rebate to the right of the junction used to be married to the edge of the now missing Anubis slab. The portion of head rim rebate to the left of the junction sat straight down ‘horizontally’ onto the body behind the right hand, bright green protrusion.

Single mauve dot- the head rim match that corresponds to the mauve body match depicted in the Part 22 photos. Both matches are seen in one photo below (photo 4).

Yellow dot- between and behind the first two body protrusions. This denotes the seating position of the triangular head protrusions when concertinaed together. It should be a tiny fraction higher on the body- the exact spot wasn’t yet located at the time of publishing Part 17. However, because the ‘horizontal’ part of the body at this point is so foreshortened it would be just one dot-width higher. 

Small mauve dots- this is an important 3D match that runs at 45° to the notionally vertical slab edge. That is, it ran at 45° through the slab-body join. That’s why it’s cited as a 3D match, it’s at an angle to the main matches. It starts inside the Anubis tray and ends up grazing up the outside of the head lobe past the rim extremity. The body portion resisted being detached along with the Anubis slab. This 45° degree trait along with the very fact it resisted detachment will be presented as evidence for head lobe stretch prior to shearing in due course. It’s of note that it kisses the three-way junction point on the shear line. 

CONCLUSION

Slab E, the Anubis missing slab, is the third slab after slabs A and B to have been attached to the shear line. For this reason, it’s tempting to say that it underwent the exact same departure process as those other two slabs. However, it was closer to y-axis (long axis) extremity. This means it was subjected to a greater ‘centrifugal’ force. Since it seems slabs C and D (Parts 12 and 13) were ejected purely via centrifugal forces at the extremities, it would be reasonable to suggest that the Anubis slab was subjected to a little bit of both processes. Perhaps this is why, if it does include Atum, it is such a large slab. It’s probably second only to Imhotep in size. This may explain the distinct lump in the middle of the residual tray. If all these 50-metre thick slabs were readily detachable because they represented sintered, volatile-free, spent crust, the lump in the middle would be the curvature of the body core that sat under the loose crust (and is now slowly turning into spent crust itself). This phenomenon of the slabs all being around 50 metres thick and possibly being spent crust will eventually get its own post. 

TAKE HOME MESSAGE FOR THE SUB SERIES

Regarding the evidence for head lobe stretch prior to shearing, the take home message for this post is the very straight line along the top perimeter of Anubis and the fact that it lines up with the three-way junction. Also, the 45°, 3D match that resisted detachment with the Anubis slab should be filed away for retrieval, as it were. 

Photo 4 shows a summary of the sub series theme so far. We have the straight line at the top of Anubis (fuchsia) leading up to the three-way junction (dark green), as described above. There’s also the very straight perimeter of the slab A extension (bright green) leading up to the mauve body match, as described in Part 22. The mauve head lobe match to this body match can now be seen in the same photo. The dark green dot on the head lobe is of course the head match that seated down onto the dark green body dot to form the three-way junction. Both of the straight lines form much of the two long sides of the red triangle of undisturbed body area introduced in Part 22 (marked ‘T’ with the rest of its perimeter denoted in red dots).

The straightness of these two perimeter lines has significance as is the observation that they are almost exactly the same length and join to the mauve and dark green dots. 
The fact that the mauve match and dark green match sit at either end of the base of the undisturbed triangle must also be kept in mind. All these pieces of evidence will be reiterated later and and brought together with other evidence where appropriate but highlighting the points as accumulated take home messages at the end of each post should help to prime the memory for when that happens. 

Photo 4 

 

Fuchsia- Anubis slab perimeter.

Bright green- slab A extension.

Red- rest of the undisturbed triangle perimeter. The triangle is marked ‘T’.

Yellow- slab A.

Two dark green dots- the head and body matches that constitute the three-way junction.

Mauve- head-body match at the other end of the base of the red triangle. This shouldn’t be confused with the mauve-dotted 3D match kissing the three-way junction. Both these features have been annotated in mauve for months and many posts, prior to being brought together in this post. It seems best to stick with precedent and point out the possible confusion. Apologies for not exploiting the full colour palette.

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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