The tenth planet discovered

Astronomers at the California Institute of Technology announced that they had found what they believe is the 10th and most distant planet in our solar system - a lump of rock and ice, similar to Pluto.

It is a tiny white dot even in the most powerful telescopes, but a dot that moves, albeit slowly, against the background of distant stars.

That means it must be a planet, so now object 2003UB313, spotted two years ago by astronomers in California, has been officially identified as the 10th planet in the solar system, and tentatively christened Xena, Independent reports.

The body is believed to be about 1,700 miles in diameter, about a quarter the size of the Earth, and about one-and-a-half times the size of Pluto, the ninth and last planet to be discovered, in 1930.

But at nearly 10 billion miles out, Xena is the most distant object detected orbiting the Sun, three times as far out as Pluto and 97 times as far out as the Earth. Its full orbit takes 560 years.

Like many other new wonders, Xena has emerged from California, having been discovered by astronomers at the Mount Palomar observatory near San Diego run by the California Institute of Technology (Caltech). Michael Brown, Caltech's professor of planetary astronomy, and his colleagues Chad Trujillo of the Gemini Observatory in Mauna Kea, Hawaii, and David Rabinowitz of Yale University, first photographed it on 31 October 2003, with the 48in Samuel Oschin telescope, normally used to track asteroids that might pose a collision danger with the Earth.

Michael Brown, a planetary scientist at the California Institute of Technology, announced the discovery over the weekend. But according to the South African Sunday Telegraph, the briefing was hastily arranged after Brown received word that his secure website containing the discovery had been hacked. The unnamed hacker was threatening to release the information, according to Inquirer.

It transpired that Brown and his friends had been sitting on the information since 2003 when they snapped it with a 122cm telescope at the Palomar Observatory. However they couldn’t confirm much about it until it was analysed again last January.