PhilStooke

PhilStooke, 6 days ago to random

China's Chang'e 2 spacecraft mapped the Moon in support of later landings including a 7 m/pixel global photomosaic. Later it was redirected to fly past Toutatis. This is a composite of several images taken by a small monitoring camera. There are a few craters but as you can see most of the surface is undulating but not obviously cratered. The image is courtesy CNSA who luckily have adopted basically the same image use policy as NASA.

PhilStooke, 6 days ago to maps

Another version of the map with radius contours (numbers in kilometres). The outline of the map is the shape's convex hull so it doesn't show the deep valley which divides the asteroid into two lobes. Of course, what we really need is a flyby mission with a camera. Luckily there was one later. #maps

PhilStooke, 8 days ago to maps

Here is a 'finder chart' (a term borrowed from astronomy. Don't tell anyone) for the Chang'e 6 landing site. #maps

PhilStooke, 9 days ago to maps

Departing from the current theme today: it appears the Chang'e 6 landing has been successful, so here is an updated lunar sites map:

https://www.dropbox.com/scl/fi/tebyydtb4cqyv1ubr6dxp/moon-site-map.png?rlkey=cqdpr8hf2ubsdobldlmeedu22&dl=0

(53 MB download, PNG file)

#maps

PhilStooke, 11 days ago to maps

And this map shows the radius in kilometers as it varies over the nucleus. Read the paper here:

https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1991A%26A...248..656S&defaultprint=YES&filetype=.pdf

(let me know if the link doesn't work).

Unfortunately for us, it's all hogwash! This paper:

Belton, M.J. et al., 1991. The spin state and homogeneity of Comet Halley's nucleus. Icarus, 93(2), pp.183-193. https://doi.org/10.1016/0019-1035(91)90207-A

gives a different rotation state, so the images show different parts of the nucleus than we expected, and Halley has long axis rotation. #maps

PhilStooke, 12 days ago to maps

The shape model of the nucleus of Comet Halley was made by digitally manipulating a gridded ellipsoid of about the size of Halley (16 by 8 by 8 km) until its shape matched every image in the data set. There are no images suitable for stereoscopic viewing to add to the shape. This map shows the locations of limbs (edge of sunlit disk, dark lines) in the images and terminators (sunrise/sunset lines, gray areas). Uncertainties are quite large. #maps

PhilStooke, 13 days ago to maps

That let Abergel calculate the viewing direction for each image. I used that to estimate a shape represented by this set of images. Numbers define individual Vega images. Giotto basically zoomed in on a single view. The camera's mirror didn't survive to view the departing view. These grids can then be overlaid on images to try to locate features. There aren't many features to locate! #maps

PhilStooke, 16 days ago to random

I reprojected each image to fit the grids to a cylindrical map projection. Then I did the same reprojection with an identical but ungridded image. Fitting them together gave me this initial map.

PhilStooke, 18 days ago to random

This shows the shape model as a map grid wrapped around images. The surprise here is that the rotation axis coincides with the long axis of the shape. This is not stable but several elongated objects seem to have this sort of rotation combined with rapid precession which makes them appear to wobble chaotically - but it's not really chaotic. Halley's comet may be doing this as well. How will this look in a map? All will be revealed.

PhilStooke, 21 days ago to random

Here is a map of Comet Borrelly, The top image is a cylindrical projection, showing only the northern hemisphere illuminated. The two lower views are projected onto an ellipsoid roughly matching the shape of Borrelly. What other comets could we look at here?

PhilStooke, 22 days ago to random

And from that study and an LPSC poster in 2009 I was able to sketch a lat-long grid on the image. It's rough and the data are not really good enough to do any better. But it is a start. If I have an image with a grid I can warp it so the grid lines fit a map projection. So that's where this is leading.

PhilStooke, 25 days ago to random

Follow some of story of the map here:

http://www.unmannedspaceflight.com/index.php?showtopic=4254&st=0

And for the full size map in all its glory, go here:

https://sbnarchive.psi.edu/pds3/multi_mission/MULTI_SA_MULTI_6_STOOKEMAPS_V3_0/document/00_map_guide.html#eros

And here is a reduced image of my LPSC 2008 poster.

PhilStooke, 26 days ago to random

The images and the shape give us a photomosaic. I also made a shaded relief interpretation of the data, shown here. This was used by USGS as their index image for crater names at:

https://asc-planetarynames-data.s3.us-west-2.amazonaws.com/mathilde_comp.pdf

PhilStooke, 29 days ago to random

Putting all the individual projections together, we get a cylindrical projection map. The extreme elongation makes this very distorted.

PhilStooke, 29 days ago to random

And another - we did this for every image. Then each one was reprojected separately.

PhilStooke, 29 days ago to random

Here is an image of asteroid 243 Ida with a lat-long grid added. The shape model was provided by Peter Thomas. My friend Maxim Nyrtsov was visiting and helped digitize the grid intersections and reproject them to intersections on a rectangular grid to make a photomosaic.

PhilStooke, 30 days ago to random

And leaping ahead, a test map sheet, the only one I made in this format. Next we will look at how we get here.