Largest Transiting Extrasolar Planet Found Around A Distant Star

7 08 2007

reES-4 planet

Lowell Observatory Press Release

Flagstaff, Ariz.– An international team of astronomers with the Trans-atlantic Exoplanet Survey announce today the discovery of TrES-4, a new extrasolar planet in the constellation of Hercules. The new planet was identified by astronomers looking for transiting planets – that is, planets that pass in front of their home star – using a network of small automated telescopes in Arizona, California, and the Canary Islands. TrES-4 was discovered less than half a degree (about the size of the full Moon) from the team’s third planet, TrES-3.

“TrES-4 is the largest known exoplanet,” said Georgi Mandushev, Lowell Observatory astronomer and the lead author of the paper announcing the discovery. “It is about 70 percent bigger than Jupiter, the Solar System’s largest planet, but less massive, making it a planet of extremely low density. Its mean density is only about 0.2 grams per cubic centimeter, or about the density of balsa wood! And because of the planet’s relatively weak pull on its upper atmosphere, some of the atmosphere probably escapes in a comet-like tail.”

The new planet TrES-4 was first noticed by Lowell Observatory’s Planet Search Survey Telescope (PSST), set up and operated by Edward Dunham and Georgi Mandushev. The Sleuth telescope, maintained by David Charbonneau (CfA) and Francis O’Donovan (Caltech), at Caltech’s Palomar Observatory also observed transits of TrES-4, confirming the initial detections. TrES-4 is about 1400 light years away and orbits its host star in three and a half days. Being only about 4.5 million miles from its home star, the planet is also very hot, about 1,600 Kelvin or 2,300 degrees Fahrenheit.

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