Terraforming Mars. Artwork 1 of 3. Today's Mars is a cold desert world with a thin atmosphere of carbon dioxide. The orange colour is due to oxides in the rocks that trap the planet's oxygen, a form of rusting. Freezing surface temperatures average minus 62 degrees Celsius, with the carbon dioxide freezing out to form dry ice deposits. Craters on the surface show a history of meteorite impacts as well as volcanic activity. Evidence of erosion by liquid water suggests that there was once water on Mars that has now been lost to space. Underground deposits of water ice could be used to terraform Mars. This is shown in images R350/209-211.