Are the Clouds made of Water?
These pictures, taken by Mars Global Surveyor, shows proof that some of the clouds of Mars are made of water. The sequence shows actual water clouds moving across the face of Mars.
As early as 1796 scientists were reporting "yellow", and "white" or "bluish" clouds in the Martian atmosphere. However, it wasn't until the Mariner 9 mission that proof was obtained that some of the clouds were actually composed of water.