Wednesday, November 07, 2007

Record-Setting Fifth Planet Found Orbiting Nearby Star, 55 Cancri, in the constellation Cancer.

55 Cancri, which is 41 light years away and can be seen with the unaided eye or binoculars
The newly discovered planet weighs about 45 times the mass of Earth and may be similar to Saturn in its composition and appearance. The planet is the fourth from 55 Cancri and completes one orbit every 260 days. Its location places the planet in the "habitable zone," a band around the star where the temperature would permit liquid water to pool on solid surfaces. The distance from its star is approximately 116.7 million kilometers (72.5 million miles), slightly closer than Earth to our sun, but it orbits a star that is slightly fainter.

"The gas-giant planets in our solar system all have large moons," said Debra Fischer, an astronomer at San Francisco State University and lead author of a paper that will appear in a future issue of the Astrophysical Journal. "If there is a moon orbiting this new, massive planet, it might have pools of liquid water on a rocky surface."

Fischer and University of California, Berkeley, astronomer Geoff Marcy, plus a team of collaborators discovered this planet after careful observation of 2,000 nearby stars with the Shane telescope at Lick Observatory located on Mt. Hamilton, east of San Jose, Calif., and the W.M. Keck Observatory in Mauna Kea, Hawaii. More than 320 velocity measurements were required to disentangle signals from each of the planets.

"This is the first quintuple-planet system," said Fischer. "This system has a dominant gas giant planet in an orbit similar to our Jupiter. Like the planets orbiting our sun, most of these planets reside in nearly circular orbits."

The first planet orbiting 55 Cancri was discovered by Marcy and Butler in 1996; the planet, the size of Jupiter, was the fourth-known star with an exo-planet ever discovered. It orbits its star every 14.6 days.

The second, third and fourth were discovered over the next eight years.

Read more at NASA JPL

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