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A BLAST of radiation from a passing star cluster could turn out to be the cause of a mass extinction on ancient Earth.

In 2003, a team led by of the University of Kansas in Lawrence suggested that a gamma-ray burst within a few thousand light years of Earth triggered a mass extinction 440 million years ago. But proof has been elusive. Because these bursts occur when a single star explodes or two stellar corpses merge, there is little left to identify the culprit.

Unless, of course, the gamma-ray burst occurred in a massive swarm of stars called a globular cluster, which hosts many pairs of dead stars that might merge, says Wilfried Domainko of . Based on the number of star clusters in the Milky Way and the rate of gamma-ray bursts in them, Domainko calculates one probably exploded within striking distance of Earth at least once in the past billion years ().

The European Space Agency’s , expected to launch in 2013, could track the guilty cluster down. Gaia will pinpoint the position and speed of such clusters, so we can see if any coincide with extinctions.