Previous data from NASA's Phoenix mission revealed snow falling near the red planet's north pole as the seasons turned from summer to fall. At the time the air was relatively warm, so those ice crystals were most likely made from water, scientists say.

But when temperatures drop in winter to -193 degrees Fahrenheit (-125 degrees Celsius), it gets cold enough for carbon dioxide in the Martian atmosphere to freeze, creating clouds of dry ice that can reach from the poles to halfway to the equator.

(Related: "Martian-Fog Study Finds Thick Haze, 'Diamond Dust.'")

So far, no Mars landers have survived near the poles during winter. So to learn more about the carbon dioxide snow, researchers at the Massachusetts Institute of Technology