Geologic map of the Lunae Palus Quadrangle of Mars

Mars presents two different terrains, a highly cratered surface that lies mostly in the southern hemisphere and sparsely cratered plains that lie mostly in the northern hemisphere. The cause of the dichotomy is a still unsolved fundamental problem of Martian geology, analogous to the problem of continents and ocean basins in terrestrial geology. The present features of the plains in particular r