This map shows the topography of the south polar region of Mars. The data were collected by the Mars Orbiter Laser Altimeter aboard NASA's Mars Global Surveyor orbiter between 1997 and 2001. The elevation of the terrain is shown by colors, with purple and blue representing the lowest areas, and orange and red the highest. The total range of elevation shown is about 5 kilometers (3 miles). The black line shows the boundary of the south polar layered deposits, an ice-rich geologic unit that was probed by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) aboard the European Space Agency's Mars Express orbiter. The radar data indicate that the deposit is more than 3.7 kilometers (2.3 miles) thick in places, and that the material consists of nearly pure water ice, with only a small component of dust. The MARSIS team also determined that the total volume of ice in the layered deposits is equivalent to a water layer 11 meters (36 feet) deep, if spread evenly across the