Caltech astronomer finds solar system's 10th planet

A California astronomer has discovered what he believes is the 10th planet in our solar system, a group of NASA-funded researchers said on Friday.

The new planet, known as 2003UB313, has been identified as the most distant object ever detected orbiting the sun, California Institute of Technology astronomer Michael Brown said.

Brown and colleagues Chad Trujillo and David Rabinowitz have submitted a name for the planet to the International Astronomical Union and are confident it will be designated a planet. Brown did not reveal the proposed name.

The procedure for approving the new planet is somewhat hazy as no new bodies have received that designation since Pluto was discovered in 1930, Brown said.

าWe hope that it's fairly non-controversial among those who believe Pluto is a planet,ำ Brown said. 'I would say get out your pens and start rewriting the textbooks today.'

The planet is located about 14.5 billion-kilometres from the sun and is about 1 1/2 times the size of Pluto, the researchers said.

The new planet orbits the sun once every 560 years and is now at its farthest point from Earth, he said. In about 280 years, the planet will be as close as Neptune, he said.

Like Pluto, the object's surface is believed to be predominantly methane, but its size - about 2,700km in diameter - qualifies it as a planet, Brown said. Earth is about 12,700 km in diameter.

The new planet is believed to be part of the Kuiper Belt, a large ring of icy objects that orbit beyond Neptune and are believed to be remnants of the material that formed the solar system.

The new planet went undiscovered for so long because its orbit is tilted at a 45-degree angle, Brown said.