January 21, 2010 — In recent images sent back from Mars by NASA's Mars Reconnaissance Orbiter (MRO), a single impact crater was evident in the Martian landscape. In that case, 'recent' means 'some time in the last few years/decades.' In this newly released photograph from the High Resolution Science Experiment (HiRISE), a cluster of small, dark meteorite impacts are obvious, contrasting with the light dusty surface.
"A new impact will scour dust from the surface and reveal darker underlying rock," writes Nicole Baugh in the HiRISE release. "This color difference makes the craters easier to spot. Other, less dusty areas of Mars are certainly being bombarded as well, but the size of the craters makes them difficult to detect without stark color contrasts."
As smaller meteorite impacts on Mars occur with a greater frequency than larger ones, it seems reasonable to say that more small craters should be spotted by orbiting satellites. In the above scene are a cluster of mini craters (each less than 5 meters in diameter) most likely originated from one meteoroid that broke up on re-entry into the atmosphere. Once the chunk of space rock disintegrated into many pieces, a wider area was afflicted with small pockmarks.
One has to wonder what effect this might have on a future Mars colony; would it be more favorable to deal with the threat of one single impactor, causing damage to one localized area, or several, smaller impactors scattered over a region?
It would be like choosing between getting shot by a bullet or buckshot, both are deadly, but it depends on how big the target is.