Tenth Planet

Artist's concept of 2003UB313
This artist’s concept shows the planet catalogued as 2003UB313 at the lonely outer fringes of our solar system. Our Sun can be seen in the distance. The new planet, which is yet to be formally named, is at least as big as Pluto and about three times farther away from the Sun than Pluto. It is very cold and dark. The planet was discovered by the Samuel Oschin Telescope at the Palomar Observatory near San Diego, Calif., on Jan. 8, 2005.
Image credit: NASA/JPL-Caltech

A planet larger than Pluto has been discovered in the outlying regions of the solar system with the Samuel Oschin Telescope at Palomar Observatory, California Institute of Technology.

The planet is a typical member of the Kuiper belt, but its sheer size in relation to the nine planets already known means that it can only be classified as a planet, Brown says. Currently about 97 astronomical units from the sun (an astronomical unit is the distance between the sun and Earth), the planet becomes the farthest-known object in the solar system, and the third brightest of the Kuiper belt objects.

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

Brown and Trujillo 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," says Brown, who is 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–in other words, it’s not yet possible to 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.

Samuel Oschin Telescope
Since 1949 the 48-inch (1.2 m) Samuel Oschin Telescope has been quietly working to improve our understanding of the universe. It nightly scans the skies, returning discoveries that astound and amaze. Currently it operates as a robotic telescope. The data collected is beamed via microwave via the High Performance Wireless Research and Education Network to the astronomers for analysis.
Image credit: Caltech

"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.

"But we are 100 percent confident that this is the first object bigger than Pluto ever found in the outer solar system."

Determination of the upper limit of the size of the planet is constrained by results from the 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 the Spitzer is unable to detect the new planet, the overall diameter must be less than 3,000 kilometers, Brown says.

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.

 

 


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