Phoenix - spring images, HiRISE views of Phoenix after the long, long winter |
Phoenix - spring images, HiRISE views of Phoenix after the long, long winter |
Oct 26 2009, 02:14 PM
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Solar System Cartographer Group: Members Posts: 10231 Joined: 5-April 05 From: Canada Member No.: 227 |
Doug just said in another thread that he was looking for Phoenix in the new images and couldn't find it. Well, I love a challenge. So here it is:
Close-up: (REMOVED - SEE LATER POST) Context: (REMOVED - SEE LATER POST) Note that map-projected HiRISE images at this latitude are in polar stereographic projection, not a cylindrical projection. North is at the left. You might not believe this, but by blinking layers like Clyde Tombaugh I think I can match numerous points, not just the hardware. EDIT: I was a bit off. Correct locations are shown below. Phil -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke Maps for download (free PDF: https://upload.wikimedia.org/wikipedia/comm...Cartography.pdf NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Nov 11 2009, 05:01 PM
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Martian Photographer Group: Members Posts: 353 Joined: 3-March 05 Member No.: 183 |
The coldest temperatures occurred/ended at the very end of July, based on past years' TES data. Sublimation will not exceed deposition at the minimum, but rather some time later. The temperatures come up quickly (probably with a feedback involving loss of CO2 ice), so August or maybe September is reasonable. I was surprised too, so I checked. But I imagine no substantive difference from the last image to any other image until the ice starts substantially disappearing.
My impression is the images show icy areas and non-icy areas. But, that's an impression based on an imaged stretched in ways I don't know. It could as easily be thick ice with ice or frost thin enough that the underlying soil influences the albedo. It is, in any case, an albedo contrast. I say that, not because the Sun is so low, but because you can do photoclinometry on the image. The darker areas show their topography quite clearly--I can see features Phoenix saw more clearly than in the orbiter images during the mission (although not as well as the latest pre-dark images). In my opinion, you can even see shading/brightening at the margins of the bright patches. I suggest they are likely just thicker accumulations (ie, drifts). Further, it seems that troughs appear icier than ridges. When the Sun is very low or below the horizon, diffuse light dominates completely. But twilight skies are not even close to perfectly diffuse, and most of the light comes from 10-20 deg elevation at the solar azimuth +- 20 degrees or so (depends on exact conditions). Some USGS people have done shape from shading on orbiter images of twilit areas, IIRC. |
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