The new pockmarks were first noticed in August 2010, when the Mars Reconnaissance Orbiter’s low-res, grayscale Context camera saw a dark patch that hadn’t been there two years before.
Such new spots often come from impact craters left by meteorites. To confirm that, MRO’s sharp-eyed HiRISE camera went in for a closer look. While the Context camera takes wide-angles miles across, HiRISE zooms in to resolve objects the size of a beach ball.
The telephoto image revealed four distinct craters, each ringed with a dark blanket where soil was blasted out in the impact. The crater quartet could have been formed by a single meteorite that broke apart on its way through Mars’ atmosphere.
By watching the Martian terrain change beneath it, MRO helps researchers determine how often Mars gets hit by interplanetary debris. Based on the number of craters, planetary scientists gauge the age of a planet’s surface features.
Whereas the surface of a lightly cratered planet like Earth is regularly changed by volcanic, tectonic and atmospheric processes, worlds with many craters — such as the moon and, to a lesser extent, Mars — have changed little in millions of years.