Bestest Coolest Picture Ever

From time to time I find and post the "Coolest Picture Ever," usually having something to do with outer space. Got a new one today. This was shot by the HiRISE orbiter that's been circling Mars for months, transmitting images of incredible resolution and quality. Some of my previous "Coolest Picture Ever" candidates were also shot by HiRISE, and that little probe is quickly becoming one of my favorites of all time. (What, doesn't everybody have favorite space probes?)
.

What we're looking at are sand dunes on Mars. The fine orange-peely texture is the same kind of wind-driven ripples you'd see in an Earth desert, nothing special. But the dark swirls! Those are caused by dust devils--the little tornado-like vortexes you often see scooting through a field--skipping across the Martian soil. As the dust devils spin, they pick up the fine orange dust, exposing heavier volcanic sand beneath. They do their little dances and die out, leaving these delicate tendril trails in their wake.

[Edited to Add: An anonymous reader who happens to live with me said I should explain what the lighter diagonal band is. That's a steeper slope or cliff face cutting across the terrain, and the parallel gray hashmarks are little landslides that rolled down the side.]

There's more information here and a much larger version here for the truly curious. Images like these constantly renew my amazement at what science can do, and has done in just my lifetime. When I was born, we'd barely managed to loft stuff into orbit, and the best views anyone had of anything off this planet came from Earthbound telescopes. What a world! What worlds!
.