Part 53- A Small Rift in Seth


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

Key:

Yellow- the two perimeters of the rift or tear.

Fuchsia- a mini match showing how there was a bit of overlap. There’s a distinctive rectangle that’s repeated on both sides. It’s between the upper section of the fuchsia line and the yellow line above it.

The resolution in this OSIRIS narrow angle camera (NAC) photo seems to get compressed and slightly degraded by the dotting application. All photos have the original underneath them though and that seems unaffected. If in any doubt about the detail, it’s worth looking at the definitive hi-res version on the OSIRIS site which is here:

And here is the landing page for the photo, showing the meta data that’s also useful (the above link is the ‘full resolution’ link on this page):

https://planetgate.mps.mpg.de/Image_of_the_Day/public/OSIRIS_IofD_2016-08-08.html

INTRODUCTION

The recent OSIRIS NAC camera photo in the header shows a small area of Seth, about 300 metres across. It includes part of the 1.6 km x 200-metre rift outlined in Parts 48 and 49. The header for those parts is here, just for context:

Photo 2- Part 48/49 header.


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

This small part of the larger rift is the dusty area at the bottom-left of the header photo for this post. The perimeter of the rift runs diagonally from lower-right to upper-left. The top-right half of the photo is the area beyond the perimeter, which in this blog is called the red triangle. Since the equator runs down the red triangle, to one side, and the paleo equator runs exactly down its middle, we can deduce that the perimeter we see is the southern perimeter of the rift. 

In the middle of the photo there’s a small massif which is the main subject of this part. It borders the dusty area and is therefore part of the perimeter of the rift. It has a curved gouge at its base, much of which is in deep shadow in the header, so it looks like a cave. It has a humped top which hosts another much smaller, shadowed recess. This massif has rifted from the larger massif or ridge to its right and the width of the rift is about 25 metres. This rift of the massif from its perimeter seating is the main reason for this part because it’s a new discovery. However, most of the post is spent putting it context with its surroundings, namely the main 1.6-km rift it’s a part of. For this reason, the small 25-metre rift of the massif is generally called a tear so as not to confuse it with the main rift that’s 200 metres wide. 

The direction of the 25-metre tear (i.e. the tensile force vector doing the tearing) is at around 45° to the main rift perimeter. You might wonder why it isn’t at 90° like the the main rift (see the arrows in part 48, photo 6). Furthermore, you may remember that this perimeter, which is also the perimeter of the red triangle, was supposed to have stretched exactly along its length towards the long-axis tip at Apis. That’s at 90° to the opening rift vector. So why is the tear at 45°? It was most probably responding to the resultant angled force. That’s the vector-summed resultant of the rift-opening vector and the red triangle stretch vector. It has to be at some angle between the two, not necessarily 45°. It looks to be more biased to the red triangle stretch vector meaning that the physical distance moved along the red triangle perimeter by the two parting pieces was greater than the distance the massif was dragged out into the main rift area from the perimeter. It would have been dragged by what is now the opposite perimeter that was tearing away from it as the 200-metre rift started opening up. That initial tearing open of the main rift is the reason the massif has this 25-metre tear between it and the main perimeter. It almost got dragged across the rift to the other side but it resisted the pull vector albeit succumbing temporarily with a small tear. 

Photo 3- the torn massif with matching light blue lines either side of the 25-metre tear. 

Photo 4- with the red perimeter of the main rift. This photo starts to prepare us for the long-distance shots below. 

Red- the 1.6km x 200-metre rift perimeter. It bifurcates just beyond the torn massif because there’s a double match in the long-distance shot further below. 

Mauve- this is just a few dots showing the true perimeter of the other side of the torn massif. They disappear promptly because that perimeter is hidden in this view. This is again in preparation for the long shot which is from above so it shows the other side of the massif in mauve. 

Photo 5- more overlayed additions in preparation for the long shot. 

Orange dot- this is at the bottom of the 25-metre tear. This orange dot is also shown in the long shot as well as another matching orange dot on the other side of the rift, 200 metres away. That twin dot doesn’t show a 25-metre tear match because the matching shape to our massif slid across the main rift without doing the same small 25-metre tear as it broke away from the perimeter. 

Bright green- this is where the next match down the red perimeter was clamped, as per Parts 48 and 49. Since the humped massif and the bright green match below it are small matches along a much longer, matched perimeter of the rift, they would be classed as consecutive mini matches. 

Photo 6- this shows a naive version of the massif’s back perimeter in mauve. The mauve line is shown running over the top of the hump but the perimeter is actually hidden behind the hump, as mentioned above. But the hump itself approximates to the same shape as if it maintains the same profile right round to the back. It’s as if it’s been turned on a lathe. This helps visualise the massif in the long shot. 

Photos 7/8- photo 7 shows the OSIRIS photo with a slightly more naive depiction of the yellow tear i.e. the obvious tear without the subtle overlaps as depicted in the header. This is so as to be able to compare it to the very grainy close up in photo 8, which is a close up of the upcoming long shot. The key is below both photos and the unannotated versions are paired below that. The long shot is a NAVCAM photo. 


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

Mauve- the full perimeter of the torn-away massif including the back side that was out of view in the header (at upper-right).

Bright green- part of the bright green seating described above. It’s a ridge, used as a fiduciary point. 

Medium green- the small recess at the top of the hump. 

Photos 9 and 10- the unannotated versions. 

Photo 11- the first long-distance shot, paired with the original.


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

Mauve dot- this is just one dot for now, on the back of the massif so as not to clutter the photo too early on. 

Red- the 200-metre rift perimeter. This isn’t the whole rift length, just the section we’re concerned with here. The whole rift is shown in Parts 48/49. The bifurcation mentioned above isn’t shown here but is shown below. 

Bright green- the next match down the rift perimeter from the mauve massif match.

Photo 12- more overlaid additions.

Mauve- the whole perimeter of the mauve massif. You’ll need to check the unannotated version because the dots obscure the match. It’s admittedly faint, but since it’s straitjacketed by a wealth of matches either side all the way up and down the 1.6-km-long rift, we can be fairly sure it’s genuine. 

Extra red line- this is the double match along the red perimeter of the rift. 

Pale green- at the top and rather faint. This is a continuation of the red perimeter match. It was shown in red in Parts 48 and 49 but it’s pale green here because it’s less important and not strictly part of the red perimeter. It’s a match that tore from beyond the notional right hand perimeter and ended up draped across the 200-metre rift. 

Royal blue- at bottom. This is an obvious match across the rift. And yet it was inexplicably missed in Parts 48/49 with red dots leapfrogging across it with abandon. This is an example of not being focussed enough when there’s clear information hiding in plain sight. This is why the tenets of stretch are being missed. It seems most people won’t slow down enough to take in the necessary detail that’s there in the photos. In this case, I was the one not giving the picture the fullest attention I could. This blue match is certainly worth pointing out as a new mini match but it’s irrelevant to the tearing massif in this post. 

Photo 13- with another overlay.

Yellow- the tear. This is rather crude, given the width of the tear. It certainly doesn’t show the subtle curves that match on either side.

PHOTO CREDITS

FOR NAVCAM:

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 A. Cooper. 

FOR OSIRIS:

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

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