DEBRIS in the main asteroid belt has allowed astronomers to reconstruct a collision that happened 5.8 million years ago, when a 3-kilometre rock shattered an asteroid more than 25 kilometres across, forming a family of at least 39 pieces more than 2 kilometres wide.
David Nesvorny of the Southwest Research Institute in Boulder, Colorado, found the group of asteroids by searching a database for objects with orbits of similar shapes and tilts, and low relative velocities. A computer model found that the orbits of the asteroids coincided 5.8 million years ago, a sign that they were once part of the…
