Frosty blue dunes on Mars

By | March 2, 2012

This picture was taken by the HiRISE camera on board the Mars Reconnaissance Orbiter, which takes extremely detailed images of the surface of the planet. It shows wind-driven sand dunes on Mars, rippling in a similar way as on Earth. The sunlight is coming from the upper left direction, and where the light hits the surface you can see the familiar reddish cast; that’s actually from very fine-grain dust laden with iron oxide — rust!

But the shadows, where the Sun doesn’t reach, it’s cold enough that carbon dioxide in the Martian air freezes out, forming a thin layer of dry ice on the surface. In this image — where the colors have been enhanced so you can see the effects better — this shades the dunes blue. You can see the frost not just covering the dunes in general, but hiding in the troughs of the ripples too (which I think is why the sunward facing parts of the dunes can look blue; that’s from the ripple shadows). The non-color-enhanced version showing the entire dune region can be found here — and is stunning in its own right. …

via Frosty blue dunes on Mars | Bad Astronomy | Discover Magazine.

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