The north and south polar layered deposits were only discovered in the years 1971 and 1972 by unmanned probe missions from the U.S. space agency NASA. The first images of the deposits were obtained from the Mariner 9 mission and were later added to by research from NASA's Viking space missions. More detailed high resolution images of the polar layered deposits have been obtained by the Mars Global Surveyor Mars Orbiter Camera. By studying the formation of polar layered deposits clues can be obtained about the climate of Mars throughout the history of the planet.
The formation of polar layered deposits is thought to include large layers of water ice, dust and in some cases sand deposits, according to the University of Arizona. It is thought that as the climate of the planet has changed different layers of material have built up to form a protective layer over those layers of material beneath, this includes water ice that has been protected from erosion and evaporation by layers of dust and sand forming over them. The formation of polar layered deposits has covered the existing terrain making it impossible to view from images from unmanned NASA probes, and deposits have covered land formations, such as cliffs and craters.
Polar layered deposits can form at the poles of Mars to a depth of up to two miles, these deposits are visible on images from space probes where they end on the edges of cliffs, troughs and scarps on the terrain of Mars. The layers of material that has built up to form polar layered deposits are not uniform, with the length of time a climate dominated Mars leading directly to the depth of the material on the surface of the planet.
NASA images show the canyon Chasma Boreale on Mars as a good example of the formation of polar layered deposits. Sand deposits that are visible in NASA images are thought to have been formed as miles of sand dunes that covered earlier layers of ice and dust. Where the Chasma Boreale canyon ends in steep cliff faces, it appears the sand deposits within polar layers is moving to form new areas of sand dunes at the foot of steep cliffs.
