A new global map of Mars has revealed a host of valleys carved from otherwise smooth areas that might be signs of the Red Planet’s most recent ice age. The features also bolster the case for a vast reservoir of water ice just below the surface. While Mars is known to contain significant volumes of water ice at its poles, researchers have yet to prove their suspicion that water ice lurks under the rest of the planet’s dusty surface. If found in warmer non-polar regions, water ice would be an invaluable resource that could support human colonies and exploration. Whether found at the equator or the poles, water ice also might provide habitats for underground Martian life.