Spines

A piece of Mars: Here are some old dunes that look a little like vertebrae of fossils (if you think they look like dragon spines poking out of the ground then you’re playing too many video games). The white areas are stabilized and possibly lithified. The blue areas are where the dunes are being actively

Mysterious textures

A piece of Mars: Dunes don’t usually have a rough surface texture like these do. It’s not clear what’s going on. Are they ancient dunes that are being eroded? What causes this particular texture? It seems unique to high elevations on Mars. Nobody knows yet. (HiRISE PSP_009448_1670, NASA/JPL/University of Arizona)

Dune cannibals

A piece of Mars: Dunes often cannibalize each other, with new dunes forming from the sand in older dunes. Here the tan dunes have formed from the sand that made up the grayish blue dunes. Notice the banding on the bluish dunes — this is a sign of erosion. The banding is probably layering in

A beautiful tangle

A piece of Mars: Compare this with my post five days ago and you might think the scenes are similar. In fact they’re not. In the previous case sedimentary layers were carved out by the wind, leaving behind swirly patterns where resistant layers created relief. Here, the swirly patterns are inherent in the rock. These