This Viking spacecraft image of Mars shows alternating layers of ice and windblown dust near the north polar cap. Annual and other periodic climatic changes due to orbit fluctuations may occur on Mars (courtesy of USGS Image Processing Facility, Flagstaff, Arizona).
One of the first images taken at the Viking 2 landing site on Mars shows the pink sky over Utopia and the desert pavement on the ground (courtesy of NASA).
Some of the crescent-shaped dunes in this Viking image of Mars are more than a kilometer wide. The dark material that streaks from the horn-shaped features may be dust recently blown from the dunes (courtesy of NASA).
Natural Bridge, Arches National Monument, Utah (photograph by Peter Kresan).
Desert Features
Sand covers only about 20 percent of the Earth’s deserts. Most of the sand is in sand sheets and sand seas—vast regions of undulating dunes resembling ocean waves “frozen” in an instant of time.
Nearly 50 percent of desert surfaces are plains where eolian deflation—removal of fine-grained material by the wind—has exposed loose gravels consisting predominantly of pebbles but with occasional cobbles.