"These scientists have added significantly to our knowledge of planetary systems," said Morris Aizenman of the National Science Foundation's (NSF’s) Astronomical Sciences Division. "We’re rapidly gaining information about Jupiter-sized planets, their orbits and orbital distances. We hope to have enough information soon to tell us what fraction of nearby stars have Jupiter-sized planets, and ultimately, how many stars throughout the galaxy have planets of any size.”

The astronomers made the discoveries as part of a long-term project supported by NSF and NASA to survey 500 nearby stars for orbiting planets. Steven Vogt, University of California, Santa Cruz, Geoffrey Marcy of University of California, Berkeley, and Paul Butler, Carnegie Institution, along with Kevin Apps, a student at the University of Sussex, England, used the Keck I telescope in Hawaii outfitted with the “HIRES” spectrometer. They will report their findings in the Astrophysical Journal.

The six planets orbit stars that are similar in size,age, and brightness to the sun and are at distances ranging from 65 to 192 light years from earth. The planets themselves range in mass from slightly smaller to several times larger than the planet Jupiter. They are probably also similar to Jupiter in their compositions--basically giant balls of hydrogen and helium gas, according to researcher Steven Vogt. Their orbits tend to be quite eccentric, tracing oval rather than circular paths.

"It is beginning to look like neatly stacked, circular orbits such as we see in our own solar system are relatively rare," said Vogt.

The presence of a planet around a star is revealed by the variation in the star’s velocity through space as a result of the gravitational force exerted on it by the orbiting planet. Vogt and his coworkers independently confirmed this method for detecting planets recently when they were able to measure the dimming of a star as a planet passed in front of it.

In addition to the discovery of six new planets, the researchers gathered new data on four known planets, whose orbits they had previously studied. Two of them showed long-term trends in their orbits indicating the presence of a companion, which could be an additional planet. These findings are significant because previously only one other system of multiple planets, around the star Upsilon Andromedae, had been identified outside our solar system.

For more information on the planet search, see: http://www.physics.sfsu.edu/~gmarcy/planetsearch/planetsearch.html

Note: If no author is given, the source is cited instead.

• Extrasolar Planets
• Stars
• Kuiper Belt
• Astronomy
• Pluto
• Jupiter

• Gas giant
• Brown dwarf
• Red giant
• Extrasolar planet
• Equatorial bulge
• Asteroid belt