The majority of stars in the universe are believed to be in binary systems, but previously no one had produced any evidence to show that such systems could contain planets. The 20 planets that have been detected outside our solar system all orbit around single stars. "To find evidence of a planet orbiting a pair of stars means there could be more planetary systems than we previously thought," said Morris Aizenman of the US National Science Foundation.

The two stars are relatively close to each other - just 1.8 times the Earth-Sun distance (AU) apart - while the planet is orbiting them at a distance of 7 AU. "It is entirely plausible that such a planet could exist" says Richard Nelson, an astronomer at Queen Mary & Westfield College in the UK. "But the problem of microlensing observations is that they are very difficult to verify," he cautions.