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U.S. Scientists Discover Tenth Planet

01 August 2005

First object larger than Pluto found in outer solar system

A planet larger than Pluto has been discovered in the outlying regions of the solar system, according to a July 29 NASA press release.

Planetary scientist Mike Brown of the California Institute of Technology, whose work was funded by NASA, announced the discovery July 29.

"I'd say it's probably one and a half times the size of Pluto, but we're not sure yet of the final size,” Brown said. "We are 100 percent confident that this is the first object bigger than Pluto ever found in the outer solar system.”

But some scientists dispute the classification of Pluto as a planet. Scientists do not have a specific definition for the term, but a working group of the International Astronomical Union (IAU) is developing a definition. The IAU holds its next general assembly in 2006.

Brown and colleagues Chad Trujillo of the Gemini Observatory in Hawaii and David Rabinowitz of Yale University in Connecticut discovered the planet in 2003 using a telescope at Palomar Observatory in California.

The object, temporarily called 2003UB313, was so far away that the discoverers didn’t detect its motion until they reanalyzed the data in January.

According to news reports, Brown made the announcement after being notified that someone had gained illegal entry to a secure Web site that contained the discovery and threatened to release the information to the public.

During the past seven months, the scientists have been studying the planet to better estimate its size and its motions.

The planet is a typical member of the Kuiper belt, Brown said, but its estimated size in relation to the nine known planets means that it can only be classified as a planet.

The Kuiper belt is an area of the solar system beyond the orbit of Neptune. Objects in the belt are called trans-Neptunian objects or sometimes asteroids. Most Kuiper belt objects are lumps of ice with some organic (carbon-containing) material. They are the same composition as comets and many astronomers believe they are comets.

The new planet, 97 times further from the sun than the Earth, is the farthest-known object in the solar system and the third brightest of the Kuiper belt objects. The discoverers proposed a name for the planet to the IAU and are waiting for a decision. Some news reports say the discoverers are informally calling the planet Xena.

"It will be visible with a telescope over the next six months and is currently almost directly overhead in the early-morning eastern sky, in the constellation Cetus," Brown said.

Brown said the new planet orbits the sun once every 560 years.

Additional information on the new planet discovery is available at the NASA Web site.

Text of the NASA press release follows:

(begin text)

NASA
Press release, July 29, 2005

[Washington]

SCIENTISTS DISCOVER TENTH PLANET

A planet larger than Pluto has been discovered in the outlying regions of the solar system.

The planet was discovered using the Samuel Oschin Telescope at Palomar Observatory near San Diego, Calif. The discovery was announced today by planetary scientist Dr. Mike Brown of the California Institute of Technology in Pasadena, Calif., whose research is partly funded by NASA.

The planet is a typical member of the Kuiper belt, but its sheer size in relation to the nine known planets means that it can only be classified as a planet, Brown said. Currently about 97 times further from the sun than the Earth, the planet is the farthest-known object in the solar system, and the third brightest of the Kuiper belt objects.

"It will be visible with a telescope over the next six months and is currently almost directly overhead in the early-morning eastern sky, in the constellation Cetus," said Brown, who made the discovery with colleagues Chad Trujillo, of the Gemini Observatory in Mauna Kea, Hawaii, and David Rabinowitz, of Yale University, New Haven, Conn., on January 8.

Brown, Trujillo and Rabinowitz first photographed the new planet with the 48-inch Samuel Oschin Telescope on October 31, 2003. However, the object was so far away 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.

"It's definitely bigger than Pluto," said Brown, who is a professor of planetary astronomy.

Scientists can infer the size of a solar system object by its brightness, just as one can infer the size of a faraway light bulb if one knows its wattage. The reflectance of the planet is not yet known. Scientists can not yet tell how much light from the sun is reflected away, but the amount of light the planet reflects puts a lower limit on its size.

"Even if it reflected 100 percent of the light reaching it, it would still be as big as Pluto," says Brown. "I'd say it's probably one and a half times the size of Pluto, but we're not sure yet of the final size.

"We are 100 percent confident that this is the first object bigger than Pluto ever found in the outer solar system,” Brown added.

The size of the planet is limited by observations using NASA's Spitzer Space Telescope, which has already proved its mettle in studying the heat of dim, faint, faraway objects such as the Kuiper-belt bodies. Because Spitzer is unable to detect the new planet, the overall diameter must be less than 2,000 miles, said Brown.

A name for the new planet has been proposed by the discoverers to the International Astronomical Union, and they are awaiting the decision of this body before announcing the name.

For more information on the discovery and to view images, visit: http://www.nasa.gov/vision/universe/solarsystem/newplanet-072905-images.html

For information about NASA and agency programs on the Web, visit: http://www.nasa.gov/home/index.html

(end text)

(Distributed by the Bureau of International Information Programs, U.S. Department of State. Web site: http://usinfo.state.gov)