HiRISE images

A piece of Mars: What are those dark, flat circles and why are there little dunes sitting on top of them? They're probably old impact craters that got filled in with dark sediment, and were then eroded flat. So you're seeing the old crater floors -- the crater rim and ejecta have all been eroded away. Dunes have formed out of some of the dark sediment that's slowly eroding away. (HiRISE ESP_029422_2055 NASA/JPL/University of Arizona) read more ❯

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) read more ❯