First evidence for planet orbiting a binary star
Nov 5, 1999
Astronomers have found evidence for a planet three times the mass of Jupiter orbiting a binary star system some 20,000 light years from Earth. The astronomers from the US, Israel and Australia used gravitational lensing data collected by the MACHO collaboration to detect the planet. When an object passes between an observer and a distant star, its gravitational field causes the star to appear brighter for a short period of time. However, the brightness pattern for MACHO-97-BLG-41 was too complex to be produced by a single star, which indicated the presence of a binary star system (Nature 402 57).
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.