Mars hosts the most extreme terrain in the solar system. Olympus Mons is the tallest volcano, rising 21.9 kilometers — about two and a half times the height of Everest. Valles Marineris is a canyon system stretching 4,000 kilometers long and up to 7 kilometers deep. It would span the entire continental United States.

The planet has polar ice caps made of water ice and dry ice (frozen CO2). During Martian winter, the CO2 caps grow as atmospheric carbon dioxide freezes directly onto the surface. In summer, they shrink and release gas back into the thin atmosphere.