METEOROID impacts can give facelifts to asteroids, apparently knocking hundreds of millions of years off their actual age.
Peter Thomas of Cornell University in Ithaca, New York, and his colleagues studied the asteroid Eros and noticed that 40 per cent of the asteroid’s surface had far fewer craters than the rest of it. Thomas thinks a collision with a meteoroid caused an asteroid-quake, and the seismic waves set Eros shaking so hard that small craters in a wide area around the crash site were smoothed out. “One impact can completely re-set a surface,” says Thomas.
Because craters are used to determine an asteroid’s age – the more craters, the older the asteroid – Thomas urges care when using crater counts (Nature, vol 436, p 366). “You could be fooled into thinking it’s a factor of 10 younger than it is.”
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