Crater on North Polar Layered Deposits. Credit: NASA/JPL/University of Arizona
The north polar layered deposits, and the bright ice cap that covers them, are very young (by geologic standards) features. To try and figure out the age of an area, or how quickly it’s being resurfaced, planetary scientists count up the number of craters at different sizes. An older surface has more time to accumulate more craters whereas a younger surface, or one that has a lot of geologic activity that destroys craters, doesn’t have many impact craters.
These polar deposits have a very low crater count so it is possible that the ice cap (bright white in this image) might only by about 10,000 years old and the surface of the layered deposits (orange-brown in this image) may be only a few million years old. This sounds like a long time but is very short compared to other surfaces on Mars.
The ice has not melted because it is being sheltered from the sun by the high crater walls, keeping the contents of the crater well preserved.
So much for Mars being a dead planet, what with ice, avalanches, rain, moving sand dunes and weather systems, it seems quite alive!
