Planetary scientists have for the first time precisely dated a collision that smashed an asteroid into fragments. The breakup is so recent–just 5.8 million years ago–that the pieces probably haven't been altered by contact with one another, other space debris, or cosmic rays.
These pristine fragments could reveal how easily an asteroid breaks apart and whether a space rock on a collision course with Earth could be destroyed by a nuclear blast. The fresh collision may also shed light on planet formation, notes David Nesvorny of the Southwest Research Institute in Boulder, Colo.
He and his colleagues searched for clusters of asteroids that have similar orbits and surface reflectivity. The most intriguing cluster, dubbed Karin, is composed of 39 rocks ranging in diameter from 2 to 19 kilometers and lies in the outer part of the asteroid belt.