This color-enhanced image shows layers of ice (in blue) exposed on a steep cliff on Mars. The layers of frozen water are about 260 feet (80 meters) thick. They probably were deposited as snow million of years ago, when Mars was tilted at a different angle on its axis, producing a wetter climate. Such layers could provide a resource for Mars colonists. They also could help scientists learn about Mars's climate history by preserving conditions that were present in different periods in the planet's past. The image was snapped by a camera aboard Mars Reconnaissance Orbiter. [NASA/JPL/UA/USGS]