#MarsWalk Day 127, 744.5 km

Not much of interest on Mars or its surrogate, Earth, this week. Decent, unexceptional distance, no noteworthy milestones or landmarks. Except, well, here’s last week’s picture again, from the THEMIS Day IR mosaic:

Screenshot 2016-05-06 20.44.42

See the prominent little crater near bottom center? I went bang through the middle of it on Wednesday.

Here’s the same area in the THEMIS Night IR mosaic:apsus night IRNot exactly a lot more interesting, generally, except for that even littler crater to my north. What the heck’s going on there? It and the surrounding area are much more bright (relative to the rest, at least) in the infrared at night than in the day.

What’s happening there is, well, I don’t know. Clearly it’s warmer at night than the surrounding area. Looks like it has to do with ejecta from the crater: maybe it’s darker, so it absorbs more heat during the day? Why not the other craters, though? Maybe this is a much more recent crater, and the ejecta around the other craters has lightened with exposure?

Apparently I’m not the only person who thought this crater looked interesting, because HiRISE took a picture of it. Here is the IRB color version (cropped):crater may 2016Wow. So what’s an IRB color? According to their information sheet, that means “3-color image consisting of IR, RED, and BG images. The IR and BG images have been warped to line up with the RED.NOMAP image” I love it when they define acronyms in terms of acronyms. They don’t go out of their way to say so explicitly, but apparently this means images in infrared, red, and blue-green wavelengths.

So why the blue streaks? “Dust (or indurated dust) is generally the reddest material present and looks reddish in the RGB color and yellow in the IRB color. Coarser-grained materials (sand and rocks) are generally bluer (or sometimes purplish in IRB color) but also relatively dark, except where coated by dust. Frost and ice are also relatively blue, but bright, and often concentrated at the poles or on pole-facing slopes. Some bedrock is also relatively bright and blue, but not as much as frost or ice, and it has distinctive morphologies.” In this image the blue streaks are stronger on the south side of the crater — facing the north pole — so my guess is it’s likely to be frost.

MarsWalk spreadsheet

MarsWalk kmz file (for Google Earth — View >> Explore >> Mars)


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