PhilStooke

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.

PhilStooke, 1 month ago to random

This somewhat less attractive set of map sheets makes up the southern side of Gaspra. The globe effect would be better if the maps were divided into more sections (gores) but this works surprisingly well. I have globes like this of Phobos and Deimos plus the northern side of Gaspra. But it really is tricky to do!

I have been involved with this for 40 years but I realize maps like these are rarely seen by others, so I'm putting them out there.

Next: time to move on to Ida.

PhilStooke, 1 month ago to random

An unanticipated bonus from these Gaspra maps is that the map sheets fit together to make a globe. Not exactly perfect but pretty darn good. I join them and print them in the format shown here. Cut them out carefully, leaving a strip of paper on one side of each gap. Then with surgical precision - it's not easy - they can be joined. This set of 7 sheets makes the northern hemisphere of Gaspra, which I have done (as Arne Saknussem might say). Same for Phobos and Deimos on yesterday's link.

PhilStooke, 1 month ago to random

And sheet 2. My Gaspra maps and many others are in NASA's Small Bodies Node of the PDS, here:

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

I only just noticed that some of their links are broken, always to the ones with labelled grids. I think this is because of an update which changes the way some coordinates are defined.

Spoiler alert - that page will lead to lots of maps of other bodies which I will be posting about later. So do not look past Gaspra! I know I can trust you because you are on the Internet.

PhilStooke, 1 month ago to random

For Phobos and Deimos I divided the global maps into 14 map sheets which were each 60 degrees across. I did the same for Gaspra and a few sheets for Mathilde, plus an experimental sheet for Ida, before I moved on to other things. This image shows the global layout of the Gaspra map sheets. On a sphere the six sheets on either side of the equator would be identical in shape, but the elongated shape of Gaspra expands those sheets at either end.

PhilStooke, 1 month ago to random

Second, the photomosaic is projected onto a grid oriented to maximize viewing of the highest resolution imaging in a single map. Here I am exploring different ways to map a body, and we are not finished yet. What about dividing the full map into separate map quadrangles? Can we make a globe of this little world? All will be revealed...

PhilStooke, 1 month ago to random

And a cylindrical map. Don't let people tell you there is one best way to make a map, one 'best' map projection etc. Cartographers want as many tools as possible to select the most useful for any given application. I once had a senior astronomy professor tell me there was no need for map projections any more because we could paste images onto a digital shape model and view it from any direction. Oblivious to the fact maps are needed to make that happen! (and global images are useful).

PhilStooke, 1 month ago to random

Secondly, a shaded relief interpretation can be drawn. This was originally drawn by hand using pencils. It was actually drawn in two separate views of opposite sides of Gaspra in a different projection and then combined here. Now most shaded relief is rendered by software from a digital elevation model but our shape model is much lower resolution than the images. Besides, this is art, not some AI crap. Not great art, I was still learning.

PhilStooke, 1 month ago to random

Michael is right, of course, that Gaspra is not tumbling, but there are things in complex rotation states. Often it's not really tumbling (which to me implies chaotic motion), it is a very slow rotation combined with rapid precession. A worse problem is an object like Mathilde which rotates so slowly that images don't reveal the rotation state.

Michael's comment about the axis is good, but I would define that as north on that body. Mathilde - just an arbitrary choice. We'll see it soon.

PhilStooke, 1 month ago to random

Peter Thomas gave me the shape model and I adapted it to my software to generate latitude-longitude grids (or graticules) corresponding to each image. The grids can be laid over the images to locate features for mapping. Here is a full set of grids. Read more here:

Stooke, P.J., 1996. The surface of asteroid 951 Gaspra. Earth, Moon, and Planets, 75, pp.53-75.

And also:

Stooke, P.J., 1996. Linear features on asteroid 951 Gaspra. Earth, Moon, and Planets, 74, pp.131-149.

PhilStooke, 1 month ago to random

And here is Deimos. There was a poor shaded relief map but it was not very useful so I made a global photomosaic of Deimos using all available images.

I am travelling for the next 3 weeks and will not be working on this during that time. I will come back to this on about May 6th and we will start looking at maps of some other worlds. 5/n