Search for massive 'Planet Nine' begins
New addition to solar system could be 10 times the mass of Earth
Scientists have found evidence of a ninth planet in the solar system which is travelling on a bizarre elongated orbit.
The body, which has been dubbed 'Planet Nine', is 10 times the mass of Earth and takes between 10,000 and 20,000 years to orbit the Sun. It is so big that researchers have branded it 'the most planet-y planet of the solar system'.
It was found by researchers at the California Institute of Technology who were puzzled as to why 13 objects in the Kuiper Belt - an area beyond Pluto - were all moving together as if being 'lassooed' by the gravity of a huge object.
After running computer simulations to see what was having an effect, they found that only a massive planet could be causing the strange movement.
Prof Martin Rees, Britain's astronomer royal, said that telescopes should be able to see the planet.
"If it exists, it should be detectable," said Prof Rees. "So we must wait until searches with big telescopes have been carried out. These are indirect arguments, but they should motivate a more intensive search for an inferred faraway planet."
Researcher Dr Mike Brown, who discovered evidence for the planet with Dr Konstantin Batygin, said that it was so large that there should be no debate about whether it was a true planet.
Unlike the class of smaller objects now known as dwarf planets, 'Planet Nine' gravitationally dominates its neighbourhood of the solar system - one of the key tests for planet classification.
Pluto used to be regarded as the ninth planet but was downgraded in 2006 to a dwarf-planet or 'plutoid' and is now known unceremoniously as 'asteroid number 134340'.
"This would be a real ninth planet," says Dr Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.
Mr Brown's earlier research helped to demote Pluto after other small, icy bodies were found beyond Neptune. "All those people who are mad that Pluto is no longer a planet can be thrilled to know that there is a real planet out there still to be found," he said.
Dr Brown, who tweets under the handle @plutokiller, added: "My daughter is still kind of mad about Pluto being demoted. She suggested a few years ago she'd forgive me if I found a new planet. So I guess I've been working on this for her. There have only been two true planets discovered since ancient times, and this would be a third. It's a substantial chunk of our solar system that's still out there to be found, which is exciting."
Dr Batygin, an assistant professor of planetary science, added: "For the first time in over 150 years, there is solid evidence that the solar system's planetary census is incomplete."
Dr Robert Massey, of the British Royal Astronomical Society, said the planet would be cold and dark. "It's a very long way away and our Sun would appear as a very bright star in the sky," he said.
Dr Brown and other colleagues have begun searching the skies for 'Planet Nine'. Only its rough orbit is known, not its precise location. The team reported their findings in the 'Astronomical Journal'. (© Daily Telegraph, London)