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Cool image time! The Mars Reconnaissance (MRO) science team today released a captioned image of several ghost dunes on Mars. The image on the right is cropped and reduced to highlight one of those ghosts, which the scientists explain as follows.
Long ago, there were large crescent-shaped (barchan) dunes that moved across this area, and at some point, there was an eruption. The lava flowed out over the plain and around the dunes, but not over them. The lava solidified, but these dunes still stuck up like islands. However, they were still just dunes, and the wind continued to blow. Eventually, the sand piles that were the dunes migrated away, leaving these “footprints” in the lava plain.
The location of these ghost dunes is inside the southeast edge of Hellas Basin, what I call the bottom of Mars.