Snows On Mars

Researchers using data from the Mars Reconnaissance Orbiter have established that carbon dioxide snow falls over at least the southern polar regions of Mars.  The planet has an ice cap topped by carbon dioxide, or dry ice, over its south pole, so the snow may be one way the cap is maintained.

We already knew water-ice snow-- the stuff we have on Earth-- falls in the northern polar region.  Carbon dioxide snow forms at much lower temperatures than the water-ice variety; Earth never gets cold enough for that.  So, Mars is the only planet in the Solar System to have two distinct types of snow fall to its surface.