Washington: Using radar data from NASA's Mars Reconnaissance Orbiter (MRO), scientists have found a record of the most recent Martian ice age recorded in the planet's north polar ice cap. The new results agree with previous models that indicate a glacial period ended about 400,000 years ago as well as predictions about how much ice would have been accumulated at the poles since then. The researchers identified a boundary in the ice that extends across the entire north polar cap. Above the boundary, the layers accumulated very quickly and uniformly, compared with the layers below them. "The layers in the upper few hundred meters display features that indicate a period of erosion, followed by a period of rapid accumulation that is still occurring today," said planetary scientist Isaac Smith who was with Southwest Research Institute in Boulder, Colorado at the time of the study The results will help refine models of the Red Planet's past and future climate by allowing scientists to determine how ice moves between the poles and mid-latitudes, and in what volumes. Mars has bright polar caps of ice that are easily visible from telescopes on Earth. A seasonal cover of carbon-dioxide ice and snow is observed to advance and retreat over the poles during the Martian year. During summertime in the planet's north, the remaining northern polar cap is all water ice; the southern cap is water ice as well, but remains covered by a relatively thin layer of carbon dioxide ice even in southern summertime. But Mars also undergoes variations in its tilt and the shape of its orbit over hundreds of thousands of years. These changes cause substantial shifts in the planet's climate, including ice ages. Earth has similar, but less variable, phases called "Milankovitch" cycles. Scientists produced images called radargrams that are like vertical slices though the layers of ice and dust that comprise the Martian polar ice deposits. For the new study, researchers analysed hundreds of such images to look for variations in the layer properties. On Earth, ice ages take hold when the polar regions and high latitudes become cooler than average for thousands of years, causing glaciers to grow toward the mid-latitudes. In contrast, the Martian variety occurs when -- as a result of the planet's increased tilt -- its poles become warmer than lower latitudes. During these periods, the polar caps retreat and water vapour migrates toward the equator, forming ground ice and glaciers at mid-latitudes. The upper unit identified by Smith and colleagues reaches a maximum thickness of 1,050 ft across the polar cap - which is equivalent to a 2-foot-thick global layer of ice. "This suggests that we have indeed identified the record of the most recent Martian glacial period and the regrowth of the polar ice since then,a added Smith, now with the Planetary Science Institute in Tucson, Arizona. Using these measurements, we can improve our understanding of how much water is moving between the poles and other latitudes, helping to improve our understanding of the Martian climate," he added in a paper published in the journal Science.