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Astronomers Discover 2 New Planets Around Giant Stars
Digitized Sky Survey image of the star HD 59686 Right: Digitized Sky Survey image of the star HD 59686

A team of astronomers has announced the discovery of two new planets orbiting giant stars, bringing to 118 the total number of known extrasolar planets. At least seven substellar companions have been found orbiting K-type stars, providing evidence that a planet can survive the evolution of its host star into a giant.

K stars are older and redder than our Sun, and represent the expanded remains of once-younger stars. Several billion years from now, our own Sun will evolve into a K star. The Earth will receive about 60 times more radiation than it does today and the temperature will rise to several hundred degrees Celsius. Observing the fate of companions of other stars late in life provides a glimpse into the future of our own solar system.

In a report at the American Astronomical Society meeting in Atlanta, Georgia, the team described four new companions to giant stars, two of which are of brown dwarf mass. A brown dwarf is neither a planet nor a star -- it never becomes massive or hot enough to ignite the nuclear fusion that occurs in a star, yet it lacks some characteristics of a planet.

Of the planetary candidates, one orbits the star 91 Aquarius, 146 light-years away. It has a minimum mass about three times that of Jupiter and orbits its host star once every 182 days. The other planet orbits the star HD 59686 once every 303 days and has a minimum mass of six-and-one-half Jupiters. Located 299 light-years away, the star has a magnitude of 5.5 and should be visible to the unaided eye under favorable circumstances.

The discoveries were made with the Doppler technique, where the gravitational pull of the planet causes a wobble in the measured velocity of the host star. The observations were carried out with the Hamilton echelle spectrograph at the University of California's Lick Observatory as part of a survey of 182 K-giant stars.

For more information on extrasolar planets, visit NASA's PlanetQuest website.
Written by Randal Jackson/PlanetQuest