Part 66- The Final Approach Ma’at 02 mosaic 

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


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

INTRODUCTION

This post is concerned with the viewing perspective of one of the last photos taken by Rosetta as she approached the comet on her controlled crash trajectory. This occurred on the 30th September 2016 at about 10:20 UTC and the photo was of the pit called Ma’at 02, which was the focus of Parts 62 to 64. The mosaic in the header is in effect a single photo of the area around Ma’at 02 and in this sense it’s is a bit confusing because the constituents are overlapped. It’s even confusing once it’s been stitched together because we’re looking at Ma’at 02 ‘upside-down’ in relation to the usual views we have of this pit. It’s something of an illusion and will be explained below. 
Ma’at 02 is also known as Deir El-Medina. That’s its recent new name but its still referred to as Ma’at 02 for clarity and brevity on this blog.

The upside-down illusion regarding Ma’at 02 will be crucial in understanding an upcoming post which is to do with two similar photos of Ma’at 02 that were used in a scientific paper. 

For readers wondering what happened to the rest of the Ma’at pit delamination series, this will be resumed in due course with at least two more parts to add to the three parts mentioned above, 62-64. They will be presented with a reminder that all five are linked as a series. 

PHOTOS

Photo 1- the mosaic (header reproduced).


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

The mosaic of Ma’at 02 is essentially a radially exploded photo. The pit is in the middle and every photo to the left, right, up and down overlaps with the last one towards the pit at the centre as you progress to the edge of the frame in four directions. Put another way, if you cut out all the photos and then concertinaed them together carefully so there were no overlaps, you’d see a single, faithful image of the pit and its surrounding terrain (see photo 2).

Photo 2 (2nd header, reproduced)- this is a stitching together of the constituents of the mosaic as described above. H/T to Gerald, a Rosetta blog commenter, for doing this so neatly. Gerald did just the stitching. All later annotations on this stitched version using coloured dots are mine, and of course the usual ESA/OSIRIS credit applies for the photo mosaic itself. 


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

It might seem as if that’s that and we can move on to other things. After all, if we toggle between the stitched view and the classic overhead view of Ma’at 01, 02 and 03 that was presented in Parts 62-4, the two seem to look as if they’re from a similar perspective, one viewpoint tipped up just a bit with respect to the other:

Photos 3 and 4- toggling between the stitched and classic views. Ma’at 01, 02 and 03 are dotted blue and 02 is in the middle. 


Photo 3 credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA/GERALD/A.COOPER

Photo 4: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA/A.COOPER

However, looking more carefully, we can see that the stitched viewpoint is actually upside-down when compared with the usual ‘upright’ views we get of Ma’at 02. 

These classic views are shown in photos 5 to 7. They’re classic in the sense that the duck-shaped comet is upright i.e. in ‘upright duck’ mode with the head lobe above the body lobe. 

Photo 5- this is a NAVCAM photo taken from above the head lobe.
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER
Ma’at 02 is marked with a single light blue dot in photo 5. This photo shows the head rim as being brighter than the body which helps differentiate the two. The differentiation is less clear in photo 6, which is almost the same view but more detailed because it’s an OSIRIS photo. 

Photo 6- another one from above the head lobe. The toggling view in photo 4 is a close up of this photo. Ma’at 02 is light blue again. 
Copyright: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA/A.COOPER

Photo 7- the classic side view. 
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

Photo 8- this is the photo 7 view with the two viewing perspectives from photos 3 and 4 superimposed.
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

As you can see, the two views are wildly off with each other, over 90° in fact, and certainly not similar viewpoints. We haven’t gone ‘upside-down’ yet so it might appear a bit confusing until you get to photo 10, which comes soon. 

Red is the classic overhead viewing direction or vector (the viewpoint in photo 3) and yellow is the stitched view (photo 4). Arrows show the direction of viewing. 

Since we’re viewing both vectors from almost overhead, it’s not showing the vectors’ angles with the surface (~40°) so much as their angle to the latitude and longitude lines of the comet if those lines were superimposed. The angle with the local average surface is known as the altitude angle and the angle with the lat/long lines is known as the azimuth angle. So photo 4 shows primarily the azimuth angles. But since we’re off to one side slightly (to the left) we can see under the two lines just a bit which betrays a little of the altitude angle. Photo 9 shows the altitude angles very well. 

Photo 9- this is a side view which shows the altitude angles of both viewpoints. Yellow is the viewing vector for the stitch. Red is the viewing vector for the classic top-down view. 
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

But it doesn’t quite end there. Photo 10 gives the true viewing orientation as we look at Ma’at 02 along the yellow stitch vector (and the classic red view for comparison). 

Photo 10- The viewer’s position is upside-down. 
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0/A.COOPER

This means that what looks like a similar viewpoint in photos three and four is only apparently similar and in fact 100 degrees off. 

Understanding the capacity for this Ma’at 02 perspective phenomenon to trip us up will be crucial to the next part. It’s going to be instrumental to showing that evidence for recent morphological changes, presented in a scientific paper, is just a mirage.

MORE PHOTOS SHOWING THE MA’AT 02 UPSIDE-DOWN ILLUSION (photo credits as above). 

Photos 11 and 12- photo 11 (top) is the stitched version rotated 180° to the classic upright duck orientation. It now appears very close to the viewpoint of the classic side view (photos 7 and 16, below) but a little lower because you can see under the ledge that’s somewhat below Ma’at 02. Photo 12 is the original upside-down stitch, included for toggling.
Photos 13 and 14- this is just the pit, Ma’at 02. Photo 13 (top) is the original stitch, unrotated and photo 14 is the classic top-down view from photo 4. They look uncannily similar despite being viewed from completely different angles. 

Photos 15 and 16- photo 15 is the stitch, rotated, and photo 16 is the classic photo 7 view.

This pair shows that the views are now almost the same just by rotating the stitch to the familiar ‘upright duck’ view. This is the equivalent of inviting our upside-down lady in photo 10 to stop hanging upside down and view Ma’at 02 down exactly the same viewing vector but sitting ‘upright’ like the rest of us. 

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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