Sep 5, 2007
Cosmic detective work has traced the origin of the asteroid that hit Earth 65 million years ago, wiping out the dinosaurs (http://www.newscientist.com/article/mg14920222.600-science--pebbles-that-did-for-the-dinosaurs.html).
Astronomers know of more than 40 families of asteroids (http://www.newscientist.com/article/dn6159-asteroid-impact-debris-can-speed-to-earth.html) that are fragments of shattered larger bodies and can calculate when the break-ups happened (http://space.newscientist.com/article/mg18524835.300-asteroids-reveal-secrets-of-evolving-solar-system.html).
Earlier this year, David Nesvorny and colleagues from the Southwest Research Institute in Boulder, Colorado, US, identified a new group which they named the Baptistina family after a 40 kilometre asteroid that is its largest known member. The dinosaur-killer was probably a lost member of this family, formed by a collision in the inner part of the asteroid belt 160 million years ago.
Nesvorny's team has calculated that a 10-kilometre asteroid, one of roughly 300 chunks of the original 170-kilometre 'mother rock', would have collided with the Earth. Other fragments of this asteroid may have hit Venus, they suggest, and could have been responsible for the formation of Tycho, the youngest prominent crater on the Moon.
The composition of Baptistina matches that of impact debris found on Earth, and the researchers calculate that the chance that some other asteroid hit the Earth instead is less than 10%.