Now in orbit for more than a month, the European Space Agency's Mars Express spacecraft has been delivering mountains of data back to Earth. Here's a beautiful desktop wallpaper you can use for your computer: an image taken on January 21, 2004 of the caldera of Olympus Mons, the largest known mountain in the Solar System. Olympus Mons is 22 km high and the caldera has a depth of 3 km.