67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 45



The header shows the main orange slide component. The top line is the original seating line of the crust that slid. The bottom line is the perimeter of the slid crust itself. It’s about 450 metres away from its original seating. The crust is an ‘onion layer’ as described in Part 29. Part 42 explains how the slide could have occurred due to comet spin-up. The unannotated version of the header is counted as being part of the header for numbering purposes as is the convention in this blog. 

The second image is a gif of the two lines, superimposed over each other to show how similar they are. 

Incidentally, the other completely separate orange component (see Part 42) is currently sitting below and to the right of this main component as it’s viewed in the header. The other separate component is therefore out of frame and will be presented in due course. It’s dealt with separately because, though travelling in a notionally similar way to the main component, it behaved slightly differently.

Photo 3- the larger OSIRIS view that the header was taken from (this is rotated 90° clockwise from the original).


Photo 3 shows very nearly the whole depression at top-right. The main line of roundish features runs across the middle of the depression and another less obvious line runs up at 45° to the right from the middle of the main line. It also shows most of the feature dubbed Henrik’s pancake at the top, just left of centre. The pancake is only notionally circular and it fits to the depression (it’s part of the blue slide in Part 42).

Photo 4- The orange slide for this part is on the right. It’s only rough and shown simply for locating the position of the slide on the base of the comet.


The left hand line in photo 4 is the seating for the slide (i.e. the top line in the header for this part) and the right hand line is the actual slid crust (the bottom line in the header). The light blue line demarcates the perimeter of the depression. The bright green dot is the lowest part of the depression and of the base of the comet.


Orange- the slid crust (bottom line) and its original seating (top line). The orange slide was about 450 metres so that’s the distance between the two lines as measured along the slide vector. The slide vector happens to be exactly vertical in this view. This means that you can scroll the picture sideways (on suitable devices) so that the side of the screen partially occludes the left or right hand side of the photo. As you track along, left or right, you can see the same portion of each line disappearing in lock step, each bump and dip on the upper line disappearing at the same time as the corresponding bump or dip on the lower line. 


Photos 5 and 6


Photos 5 and 6 show the orange slide and its seating with very small dots. The photos in later parts devoted to the orange slide will have bigger dots, like the header, so that patterns can be seen at a glance. Photos 5 and 6 are more for tracing your way along the two orange lines and seeing the finer matches. 

The yellow lines in photo 6 are really part of the orange slide but they’ve been dotted yellow because they are a) delaminations that were deposited along the slide and b) are intimately related to the large, half-embedded boulder and its seating against the roundish features. The seating of the boulder’s tip is the topmost, upturned, curved V-shape. The boulder tip is also marked yellow. The lines either side of the boulder and in front of it are the delaminations. The boulder itself could also be considered a delamination. Three dots denote three bright boulders that may also have been deposited in a line along the slide vector during the slide. Notice that the boulder seating V shape is beyond the orange seating line. That’s because the boulder sat beyond the crust, and the crust broke in a curve around the middle of the boulder. That curve is the one that’s being traced in the orange lines for the main crust and its seating. This relationship between boulder and crust will get more of an airing in later parts. 

In photos 5 and 6, the matches are very faithful from the left round as far as the roundish feature, that is, the one that’s actually polygonal with a very well defined edge on both the slide and the seating. The polygonal feature is just below and to the right of the finger-like protrusion which happens to be the uppermost tip of both lines in this view. The perimeter of the polygonal feature is so thin, dark and well defined that it constitutes a match to 5 metres or less resolution, across a 450-metre gap. That one small match is the most accurate lynch pin one could hope for from which to move either side and find more matches. Moving to the left (up to the finger tip, then left) the matches were easy to find and very faithful. 

Moving to the right of the polygonal feature, the matches aren’t so obvious. However, the large boulder’s seating helps greatly (yellow in photo 6). The large boulder is really part of the orange slide but it gets yellow dots so as to tease out its complex behaviour. 

In fact, once the very fine and obvious matching has been done from the left extremity of the line, round to the polygonal feature, and the boulder also chimes in with its own match halfway along the line, these factors constrain the rest of the slid crust’s seating to run along the line shown beyond and to the right of the polygon. As you can see, it follows the roundish features as one might expect. 


The matching orange lines show that the crust slid from its seating in the depression. However, there’s a lot more to the slide than appears at first glance. It sheds light on the nature of the depression it slid from, including the roundish features. This will be dealt with in subsequent parts on the orange slide. 




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