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The Planetary Society Weblog
By Emily Lakdawalla
Newly released archive of Mars Express HRSC data, part 2
May. 3, 2006 | 18:12 PDT | May. 4 01:12 UTC
Here's the other set of images from the new public release of Mars Express HRSC data that Doug Ellison put together for me. (Here's the first set.) This one is really fun. To begin with, here is the full swath. This image covers a region near the equator, somewhat east of Meridiani Planum, from 4.6 to 10.8 degrees south and 23.9 to 26.1 degrees east. The whole strip is 383 kilometers (238 miles) long and covers an area of 45,000 square kilometers ("the exact size of Estonia, would you believe?" Doug says). At the center of the image is Pollack crater, home to a famous outcropping of resistant material that has been known as "White Rock" since Mariner 9 first photographed it. I just read up on "White Rock" in my handy copy of Bill Hartmann's book A Traveler's Guide to Mars and found that the fact that White Rock isn't really particularly white has been known since 1976, when a team led by Jim Cutts first recognized the fact that its whiteness was an optical illusion caused by the unusually dark floor of Pollack crater, but the name has stuck. Anyway, here's the image: Pollack Crater, MarsThe crater Pollack on Mars contains a deposit of apparently resistant rocks that are usually referred to as "White Rock" because they are so much brighter than the soil and rocks that surround them. However, they are -- like most Mars rocks -- actually fairly dark in color. This image was captured by Mars Express on December 25, 2004. The approximate true color view was produced by Doug Ellison from infrared, green, and blue-filtered images released to ESA's Planetary Science Archive in April, 2006. Credit: ESA / DLR / FU Berlin (G. Neukum) / Doug Ellison |
Pollack crater is nifty, but that's not why I'm showing you this picture. The reason I'm showing you this picture is for something very interesting that is going on at the very north end of the swath. Here is a cropped view of the north end of the swath. If you've got sharp eyes, you'll notice something very peculiar. Stare at it a bit before you read on (you may need to enlarge; don't worry, this one's only 97 kb)...North of Pollack crater, MarsCredit: ESA / DLR / FU Berlin (G. Neukum) / Doug Ellison |
Did you see them? Here's a clue. Look for little puffs of white with multicolored shadows. To help you, Doug provided me a version with these interesting little guys highlighted.Credit: ESA / DLR / FU Berlin (G. Neukum) / Doug Ellison |
Do you know what you're looking at yet? Those are dust devils! Mars Express color data is not captured simultaneously; the three color filters used in these pictures covered the same area about thirty seconds apart. During the time between each frame, dust devils roughly 50 meters in diameter moved, which causes them to appear as multicolored spots in this image. They cast shadows to the east-southeast as they move to the west-northwest. Very, very cool. Doug also put together animations of four color filter frames to show the dust devils in motion.Locations of dust devil animations |
| | | Martian dust devils in motion
These animations are each composed of four images captured by Mars Express HRSC on December 25, 2004. Each image was captured through a different filter: infrared, green, blue, and red. The images were captured approximately 30 seconds apart. From one frame to the next, light spots casting dark shadows can be seen to move to the north west -- these are dust devils in motion across the plains of Mars. Credit: ESA / DLR / FU Berlin (G. Neukum) / Doug Ellison |
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