Blue Like MarsThis image shows the west-facing side of an impact crater in the mid-latitudes of Mars' northern hemisphere. Like many mid-latitude Martian craters, this one has gullies along its walls that are composed of alcoves, channels and debris aprons. The origins of these gullies have been the subject of much debate; they could have been formed by flowing water, liquid carbon dioxide or dry granular flows.
Many of the other features observed in and around this crater are indicative of an ice-rich terrain, which may lend credence to the water formation hypothesis for these gullies. The most notable of these features is scalloped terrain in and around the crater. This type of terrain has been interpreted as a sign of surface caving, perhaps due to sublimation of underlying ice. Sublimation is the process of a solid changing directly to a gas.
Another sign of ice is the presence of parallel lines and pitted material on the crater floor. Parallel linear cracks are also observed along the crater wall over the gullies, which could be due to thermal contraction of ice-rich material.
together, these features are evidence for ice-rich material having been deposited in this region during different climatic conditions, material that has subsequently begun to melt and/or sublimate under current conditions. More recently, wind-blown deposits have accumulated around the crater, as evidenced by the parallel ridges dominating the landscape.
The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter took the image on April 13, 2010.
Image Credit: NASA/JPL-Caltech/University of Arizona
As always, go to NASA here for the full effect of this image.