Charitum Montes (Natural Colors; credits: NASA/MGS/MSSS)

What causes the unusual white color on some Martian Mountains? The answer can be guessed by noticing that the bright areas disappear as springtime takes hold in the South of Mars: dry ice. Dry CO2 ice sublimates directly to gas from its frozen state. The frosty mountains, named "Charitum Montes", have been covered with CO2 ice over the Martian Winter. The serene scene pictured above is not a photograph, but rather a computationally constructed digital illusion resulting from the fusion of two color images from the Mars Orbital Camera and topographic data from the Mars Orbiter Laser Altimeter. Both instruments operate from the Mars Global Surveyor robot spacecraft currently orbiting Mars.