Just take a look at this image taken by HiRISE, currently orbiting Mars. Click the image for a much larger version.
This truly is stunning, and even more so once you know what caused it. The sand-dunes on Mars are mostly made up of heavy basalt particles which are the dark grey areas, over the top of which lies a fine dusting of red sand. Dust devils regularly roam the face of Mars, and when they do, they sweep up the fine red dust in their path, creating these beautifully intricate streaks, swirls and whorls of grey.
It’s well worth going through the rest of HiRISE’s images, they’ve even got a whole bunch of stunning stereoscopic images of the surface, so get your 3D glasses on if you’ve got any lying around! :D
Originally posted on Phil Plait’s blog, Bad Astronomy