High-resolution images from the Mars Global Surveyor are throwing into doubt conventional assumptions about the Red Planet’s craters.
For years astronomers believed they accumulated over long periods of time as the planet was repeatedly hit by small meteors. Therefore, the more craters, the older the planet must be. New images indicate that most of the cavities are secondary impacts from rocks kicked up when large asteroids hit. “Most of the craters are highly nonuniform in how they are distributed across the planet,” says planetary geologist Alfred McEwen of the University of Arizona in Tucson. “The surface can go from being free of craters to being full of craters in an instant,” he says. The upshot is that despite its pockmarked appearance, the surface of Mars may be hundreds of millions of years younger than previously thought.