Even Mars has cloudy days

It can be easy to forget, but Mars has clouds very similar to the the ones you find here on Earth. Don't believe me? Here, check out the first photograph ever taken of an overcast Martian sky; or this picture of some stratus clouds, captured about 40 minutes before a Martian sunrise. The thin sheets of cotton-white goodness spread across the image featured up top? Yep, those are clouds.

The first two images were photographed years ago by NASA's Mars Pathfinder. The image up top, however, was captured much more recently by NASA's HiRISE — the most powerful camera we've ever sent to another planet.

"Generally speaking when we take an image we are not trying to capture clouds," jokes researcher Candice Hansen, who uses HiRISE imagery to study seasonal processes on the Red Planet, "but I thought these made for a dramatic picture, so I captioned it."

In this instance, Hansen says HiRISE had intended to photograph the bright ice-covered sand dunes that you can just make out beyond this blanket of condensation.

She says these clouds are typically made of water ice crystals, and that they regularly appear over Tharsis — a massive volcanic plateau close to the equator in Mars' western hemisphere. (See the huge red and brown region on the lefthand side of this view of the Martian surface? That's Tharsis.) [HiRISE]