Part 75- The Long-Axis Bes Delaminations


Please zoom the header to see the Bes delaminations. 

Photo 2- view looking down on the base. 


Red arrows in photo 2 show symmetrical delamination vectors on all four sides of the body lobe diamond. 

Photo 3- ESA regional map showing Bes, a lesser known region in the southern hemisphere of the comet. 
Bes adjoins Imhotep so it could be argued that it’s part of the comet base but a somewhat curving-away part in comparison with the flatter Imhotep area itself. Bes was often visible in the early NAVCAM photos of Imhotep in 2014. However, it was poorly lit due to being in the southern hemisphere during its winter. 
More detailed photos of the Bes delaminations follow this introduction which includes an overview of the delaminations on all four sides of the body lobe diamond. This description therefore puts the Bes delaminations in perspective as a predictable part of a larger, unfolding stretch scenario. 
The Bes delaminations separated along the expected tensile force vectors set up in a comet that has spun up to a 2- to 3-hour rotation period- just like with the other four diamond sides. This is as opposed to presenting the Bes delaminations as interesting, isolated, random scarps that happen to be parallel for no discernible reason and arranged along a vector that’s in any old direction. They’re arranged, in fact absolutely straitjacketed, in one direction: the long-axis stretch direction. 
The header photos show an overview of the delamination vectors down the four sides of the diamond-shaped base of the body lobe. The vectors are in two pairs, each pair running from one of the two short-axis tips. All four vectors stop at either one of the two flattened-off long-axis tips of the body. So they all run from short-axis tip to long axis tip, are all almost equal in length and are all relatively straight. This is indeed why the body is a stunningly symmetrical diamond shape.
The four sides of the diamond were brought about by the tensile forces of stretch running down the long axis of the body and the two flattened long-axis tips ‘pulling’ at both ends. This led to the four distinctive morphologies along each side of the diamond and these were noticed by the ESA scientists as being different. This is why those four morphologies were delineated as different regions. 
The result is that we have a situation where, on a supposedly randomly aggregated, and randomly eroding cometesimal we have four regions that just so happen to be of equal length and entirely bounded by a long axis tip and a short axis tip in all four cases (each defining one side of the body diamond). Those regions are Bes, Khonsu, Ash and Aten. 
The Khonsu delaminations have been presented already (please see the page in the menu bar). The Khonsu delaminations have also been tweeted (with annotated photos) to several ESA scientists including an OSIRIS author.
The Bes delaminations were brought forward in the blog post queue because they’re needed in order to explain the complex behaviour of the ‘first green slide’ at Imhotep. That’s one of the three green slides that were presented in Part 42 but little explanation was given for how it slid. Part 42 was only an overview of all the Imhotep slides. It showed eight slides in four colour categories. The full explanation for the first green slide will come soon and will be much easier to comprehend once the detailed photos of the Bes delaminations are understood. This is because the Bes delamination vector tugged on the first green slide too. It will be actually be called ‘the first green slide’, for want of a better term because there are two other Imhotep slides designated as green by virtue of their similar sliding behaviour. Also the one designated as first is also the most important of the three. 
The Aten and Ash delaminations remain to be presented. They behaved much the same as Bes and Khonsu through being crust forced to delaminate in order to accomodate the long-axis stretching of the comet’s core. This essentially involved stealing internal cometary matrix from the short axis and donating it to the long axis. As a result, the short axis reduced even more in length while the long axis increased even more in length. The short axis reduction was subsequently reversed somewhat by radial sliding of crust after the head sheared from the body. This is why, for example, the border between Bes and Anhur is long, straight and sharp, like a knife edge. The Cliffs of Aten are radially slid material as well and their remarkably straight edge constitutes most of the Aten diamond side. 
So although the delaminations on the four sides of the body produced the diamond, they may well have produced an ellipsoid had it not been for the further fashioning as a result of radial crust sliding. The radial crust sliding is a separate phenomenon from the core-directed long-axis delaminations even though those delaminating layers were surely sliding, in a more regimented fashion, over each other towards the long-axis tip. Radial slides were simply newly loosened pieces of crust trying to slide to a position that’s further away from the rotation axis while under the influence of the centrifugal force of spin-up. They couldn’t slide radially until loosened. Before loosening, they could only delaminate along the long-axis vector (or rather, the closest local-surface vector to the long-axis vector). And they delaminated only if called upon to do so by the exigencies of the surface crust having to accommodate the long-axis core stretch. Conversely, loosened-crust sliding respects only the rotation axis and therefore slides over the body in the direction which is the shortest distance to get away from the rotation axis. 
Whilst, the moment of head shear was responsible for the Babi and Aswan radial slides, it can’t explain the obvious radial sliding at Imhotep (e.g. blue slides in Part 42 and in fact Bes too but only *after* Bes delaminated on the long axis vector). It seems that there came a point where the Imhotep long-axis delaminations loosened the crust enough to slide radially anyway. 


Photo 4- A simple long-distance representation of the three most obvious delaminations (plus original).

Strictly speaking, there are only two delaminations in photo 4, the second and third lines on the right. The first line is their original seating. But they’re just called the Bes delaminations here for expediency. There are several less obvious delaminations added to the right of these three in later photos. 

Photo 5- same as phot 4 but also showing a red slide track. 
The red slide track in photo 5 is almost dead straight and links the tops of all three delaminations. 

Photo 6- a close up of the first and second delaminations with mini-delaminations shown as well. 
Please refer to the unannotated version to see for yourself as the annotations partially obscure the very detail they’re depicting. 
Many of the mini delaminations in photo 6 actually trace the shape of the upside-down L-shape at the top of the three delaminations. The joined-up ends of the L’s together trace the horizontal (in this view) slide track annotated red in photo 5. The other line of L’s, halfway down, trace the track of another upside-down L-shape that’s also halfway down the second delamination. 
These mini-delaminations are uncannily similar to delaminations at Aker. In Part 51, it was shown that a long, angular feature (annotated mauve in that part) had delaminated either side of the rotation plane at Aker. So it delaminated, north and south because the tensile forces of stretch turn north-south as they round the flattened long-axis tips. Between the main Aker delaminations we see mini-delaminations that are virtually identical to the ones we see here at Bes. The Aker ones are in fact neater and more obvious. However, the Part 51 photos don’t do them justice even though they are visible. I may try and find a suitable OSIRIS close-up of them and add it here in due course. 
Photo 7- same as photo 6 but with the southern perimeter of the first green slide shown. Also, two yellow triangles and their slide track. 
Notice how in photo 7, the first green slide perimeter is contiguous with the first Bes delamination. This is why the Bes delaminations affect the first green slide. The northern first green slide perimeter is just out of sight behind a ridge due to the low profile view. However, the first green slide is one of the the 17 paleo rotation plane signatures and has been presented as such on the Paleo Rotation Plane Adjustment page. It’s called the green triangle on that page. It’s an isosceles triangle, straddling the paleo rotation plane/equator and has the all-important ‘finger’ at its height vertex. The green slide was also presented in Part 42, as mentioned above, but that rendition is somewhat inaccurate, or rather, what’s shown is accurate but it doesn’t show the full perimeter of the layer that slid. In other words, it doesn’t include the full green triangle that constitutes both the first green slide and the paleo plane signature as one and the same triangular chunk of crust. This correction is simply due to studying the comet for a further 9 months since Part 42. 
Photo 8- The header overview reproduced with its  original.
Photo 9- long-distance view including the head lobe. The delaminations aren’t as accurately shown here as in above closer views because of overexposure of the actual features. The first green slide triangle adjoins the first Bes delamination. You may be able to make it out.

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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