NASA/MGS/MSSS

Mars is often depicted as a dusty place, and it is. But it can be cloudy on the red planet, too. And Martian clouds are sometimes more like terrestrial clouds than you might think.

In this photo, taken by NASA's Mars Global Surveyor and released earlier this month, clouds surround several of Mars' towering volcanoes. One of them, Olympus Mons, soars 15 miles (24 kilometers) above the surface. What are the clouds made of? Water ice, say scientists at Malin Space Science Systems, which operates the spacecraft's camera.

Most of the water on Mars is locked up in the ground and at the poles. And, so far as scientists know right now, it's all of the frozen variety. At the north pole, note the summer remains of the permanent water ice cap. [Volcanoes and Planet Building]

-- Robert Roy Britt