Baby dunes on Mars are pretty big compared to those on Earth. In this 885×512 m (0.55×0.32 mi) frame, there are four dunes of roughly the same size, all of which are about as small as dunes can get on Mars. They’re ~180 m (590 ft) across, several times bigger than similar “elementary” dunes on Earth.

There’s another key difference between Earth and Mars dunes. The avalanching lee slope (the slip face) comes to a point in these dunes. That’s because there are two winds forming these dunes, one from the upper right and one from the upper left. On Earth, as winds alternate, they erode the older slip face and create a new one directly downwind, so you wouldn’t typically see two crisp slip faces meeting at a point, like they do here. There’s something about sand or the movement of sand on Mars that makes slip face creation faster than erosion of older slip faces, so you can see two of them at once.

(HiRISE ESP_027665_2225, NASA/JPL/Univ. of Arizona)

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