Astronomers have discovered two new, giant planets around the star Upsilon Andromedae--bringing the total there to three. The findings, which have been submitted to the Astrophysical Journal, suggest that the star has a real "stellar system" that looks at least a little like our own.
In recent years, astronomers had already found some 20 planets in solitary orbits around sunlike stars--one of them completing its circuit around Upsilon Andromedae in a mere 4.6 days. Now, two international teams have found two more planets near the same star, with elliptical orbits that take about 242 and 1270 days to complete. The middle one was the most difficult to dig out of the data, says co-author Timothy Brown of the National Center for Atmospheric Research in Boulder, Colorado. "We were finally, genuinely convinced about 2 or 3 weeks ago."
The researchers have also estimated surface temperatures of the planets, says Brown. The most distant planet is below freezing, while the one in the middle is probably above the boiling point of water. As for the innermost planet, says Brown, "it's undesirable real estate." The new planets have minimum masses ranging from 0.72 to 4 times the mass of Jupiter.
The find means that there are now three stars known to have more than one planet: the sun, Upsilon Andromedae, and a spinning neutron star, or pulsar, with a trio of planets. Upsilon Andromedae's system, says Alan Boss, a planet theorist at the Carnegie Institution of Washington, does more than add to the collection of presumed planets. It also provides persuasive evidence that the objects are planets rather than brown dwarfs--stars too small to ignite nuclear-fusion reactions in their core--as some theorists have suggested. Stars and brown dwarfs simply do not turn up in arrangements so reminiscent of our solar system, says Boss. "This system, even though it's kind of overweight and kind of eccentric ... really smacks of a planetary system."