"10th Planet" Discovered

Astronomers have found a new planet in the outer reaches of the solar system.

Science@NASA
7-29-05

     July 29, 2005: "It's definitely bigger than Pluto." So says Dr. Mike Brown of the California Institute of Technology who announced today the discovery of a new planet in the outer solar system.

     The planet, which hasn't been officially named yet, was found by Brown and colleagues using the Samuel Oschin Telescope at Palomar Observatory near San Diego. It is currently about 97 times farther from the sun than Earth, or 97 Astronomical Units (AU). For comparison, Pluto is 40 AU from the sun.

     This places the new planet more or less in the Kuiper Belt, a dark realm beyond Neptune where thousands of small icy bodies orbit the sun. The planet appears to be typical of Kuiper Belt objects--only much bigger. Its sheer size in relation to the nine known planets means that it can only be classified as a planet itself, Brown says.

     Backyard astronomers with large telescopes can see the new planet. But don't expect to be impressed: It looks like a dim speck of light, visual magnitude 19, moving very slowly against the starry background. "It is currently almost directly overhead in the early-morning eastern sky in the constellation Cetus," notes Brown.

     The planet was discovered by, in addition to Brown, Chad Trujillo, of the Gemini Observatory in Mauna Kea, Hawaii, and David Rabinowitz, of Yale University, New Haven, Connecticut. They first photographed the new planet with the 48-inch Samuel Oschin Telescope on October 31, 2003. The object was so far away, however, that its motion was not detected until they reanalyzed the data in January of this year. In the last seven months, the scientists have been studying the planet to better estimate its size and its motions.

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