An international team of astronomers has found the first evidence of a planet orbiting a double-star system.p. The discovery, described in the November 4 issue of Nature, provides encouragement for scientists seeking life outside our solar system, because many, if not most, of the stars in this region of the Milky Way galaxy are thought to exist in binary, or double, systems.p. Previously, all 20 planets detected by astronomers outside the solar system had been found orbiting single stars, although some of those stars are members of binary systems.p. “Between half and two-thirds of the stars in our solar neighborhood are known to be members of binary or multiple-star systems,” said Morris Aizenman, an astronomer in the National Science Foundation’s astronomical-sciences division, which provided some of the financing that led to the discovery. “To find evidence of a planet orbiting a pair of stars means there could be more planetary systems than we previously thought.”p. The newest planet, which is estimated to be about three times as massive as Jupiter, was discovered by a team headed by David P. Bennett, an assistant professor of physics at the University of Notre Dame, and Sun Hong Rhie, a research assistant professor of physics there.p. The scientists used a technique called gravitational lensing to infer the presence of the planet orbiting the two stars, which are separated from one another by about twice the distance from the Sun to the Earth.p. The team included researchers at the Australian National University, Australia’s Monash University, and Israel’s Tel Aviv University.