Images: When Mars was a wetland

This is a composite image of Mars' northern polar cap, taken while instruments were being tested before heading into the orbiter's "primary science phase," which is set to begin the first week of November. This is a mosaic of four images taken at midnight, 6 a.m., noon and 6 p.m., made possible by the fact that the sun shines on the pole all day long during the summer.

Photo by NASA/JPL/MSSS