[/caption]This striking view of the Martian surface shows a stark contrast (false colour) between ice deposits and layered deposits (composed mainly of ice, rock and regolith) on the edge of the polar ice cap. In the centre, there is a lone crater, approximately 200 meters in diameter, collecting a basinful of ice. The ice is thought to have been there for about 10,000 years.
However, there are some oddities in this scene. Why is the crater abnormally shaped? After all, craters are normally circular, not oyster shell-shaped. Why is it an isolated crater? On viewing the entire region, only one crater appears to be present for several kilometres. Does this mean the landscape is fairly young? If so, what geological processes are shaping the surface?
The High Resolution Imaging Science Experiment (HiRISE) on board the Mars Reconnaissance Orbiter (MRO) continues to return some of the most striking views from its Martian orbit. The camera can resolve objects less than a meter in diameter, picking out everything from sand dunes, eroding mesas, rolling rocks, avalanches (in action) to tiny secondary craters. These are some of the most detailed views we’ve ever had of the Red Planet’s surface. HiRISE can even keep an eye on our robotic explorers, like spotting Phoenix shortly after it landed and the tread marks of the rover Opportunity.
Although this image of a rather odd-looking crater in the North Polar Region of Mars may seem a little mundane when compared with the list of HiRISE accolades, it is no less important. It is the sole impact crater for miles, hugging the edge of the polar ice cap, carved into layered deposits of rock, soil and lumps of ice. Using the crater count as a guide (i.e. the lower the count, the younger the surface is) HiRISE scientists believe the layered deposits may only be a few million years old. This may sound like a long time, but for a planet thought to be geologically inactive, the resurfacing rate seems pretty rapid. In this case, it is also believed the ice deposits in the crater are only 10,000 years old.
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Geological activity destroys evidence of craters, although this region will have been hit by a similar number of meteorite impacts as crater-covered regions, rapid processes appear to be constantly reshaping the landscape. It is thought that the ice flow rate would be quite low, but on observing the strange shape of the central crater, it seems it is being warped by the motion of the surrounding deposits. The bright white ice deposits inside the crater are being protected from ablation as it is being shaded from the Sun by the crater walls. This is a common feature in polar craters.
So much for Mars being a “dead” planet, then. As seen with the dynamic avalanche processes and rolling boulders, Mars is far from being geologically inactive…