Hypothetical water map of Mars. Relief map of the surface of Mars, showing what the planet could look like were it to be covered in water by the melting of its ice caps by terraforming efforts. Here, deep areas are blue to green, shallower areas are yellow and the shallowest are red. Terraforming is the theoretical process of deliberately modifying a planet's (or other body's) atmosphere or surface to be similar to that of Earth's in order to make it habitable. Based on data obtained by the Mars Global Surveyor (MGS).