Best-known comets may be visitors from other stars

Many of the most famous comets in history, including Halley, Hale-Bopp and McNaught, may have come to our solar system from elsewhere.

“Anyone who has seen a long tail comet in the night sky may be looking at material from another star,” says Professor Martin Duncan of Queen’s University, Canada.

The researchers used computer simulations to show that the sun may have captured small icy bodies from its sibling stars, back when it was in its birth star cluster.

During this time, each star formed a large number of small icy bodies – comets – in a disc from which planets formed. Most of these comets were gravitationally slung out of the disc by the newly-forming giant planets.

The sun’s cluster came to an end when its gas was blown out by the hottest young stars. The researchers’ computer models show that the sun captured a large cloud of comets as the cluster dispersed.

“The process of capture is surprisingly efficient, and leads to the exciting possibility that the cloud contains a potpourri which samples material from a large number of stellar siblings of the sun,” says Duncan.

Evidence comes from the roughly spherical cloud of comets – the Oort cloud – which surrounds the sun. Exactly how the Oort cloud was created has been a mystery for more than 60 years.

“We have a new model of how the Oort cloud formed. We’re not the first to suggest this could happen but we are the first to show it in a detailed computer simulation,” says Professor Duncan.