Spotted beyond Pluto, the tenth rock from the Sun

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.

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.

But it was so far away its motion was not detected until data was reanalysed in January. At present, Xena is near its farthest point from Earth, but in about 280 years, it will be as close as Neptune, (the eighth planet, discovered in 1846).

It has taken scientists this long to discover it because its orbit is tilted at a 45-degree angle to the orbital plane of the other planets. Xena is believed to be part of the Kuiper Belt, a great band of icy objects beyond Neptune, that are believed to be remnants of the material that formed the solar system.

"This is the first object to be confirmed to be larger than Pluto in the outer solar system," Professor Brown said, adding that although its exact size was yet to be determined, it was "definitely bigger than Pluto".

The new planet was rocky and icy, similar to Pluto, he said, and so far away an observer standing on its surface could cover the view of the sun with the head of a pin, although it was sufficiently bright for amateur astronomers to track it in the early-morning sky.

The astronomers have submitted their name for it - from the warrior princess in the 1990s TV series - to the International Astronomical Union and are confident it will be designated a planet, although the procedure for approval is somewhat hazy because no new bodies have received that designation since Pluto was found 75 years ago, Professor Brown said. "We hope it's fairly non-controversial among those who believe Pluto is a planet," he said. "I would say, 'Get out your pens and start rewriting the textbooks today'."

In classical times, before the invention of the telescope by Galileo in 1610, the solar system consisted of the Sun and just six planets: Mercury, Venus, Earth, Mars, Jupiter and Saturn.

In 1781, the German musician-turned astronomer William Herschel, working in Britain, discovered Uranus, using a telescope he made himself.

Start your day with The Independent, sign up for daily news emails
Voices
There will be a chance to bid for a rare example of the SAS Diary, collated by a former member of the regiment in the aftermath of World War II but only published – in a limited run of just 5,000 – in 2011
charity appealTime is running out to secure your favourite lot as our auction closes at 2pm today
News
people
Arts and Entertainment
Bianca Miller and Katie Bulmer-Cooke are scrutinised by Lord Sugar's aide Nick Hewer on The Apprentice final
tvBut Bianca Miller has taken on board his comments over pricing
News
Elton John and David Furnish exchange marriage vows
peopleSinger posts pictures of nuptials throughout the day
PROMOTED VIDEO
News
File: James Woods attends the 52nd New York Film Festival at Walter Reade Theater on September 27, 2014
peopleActor was tweeting in wake of NYPD police shooting
Sport
Martin Skrtel heads in the dramatic equaliser
SPORTLiverpool vs Arsenal match report: Bandaged Martin Skrtel heads home in the 97th-minute
News
newsAstonishing moment a kangaroo takes down a drone
ebooks
ebooksA year of political gossip, levity and intrigue from the sharpest pen in Westminster
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Ashdown Group: IT Support Analyst - Chessington

£25000 per annum: Ashdown Group: IT Service Desk Analyst - Chessington, Surrey...

Recruitment Genius: Technical Support Analyst / Helpdesk Support Analyst

£16000 - £19000 per annum: Recruitment Genius: Our client is the UK's leading ...

The Jenrick Group: Finance Manager/Management Accountant

£45000 - £55000 per annum + benefits: The Jenrick Group: Finance Manager/Manag...

Recruitment Genius: Manufacturing Manager

£35000 - £38000 per annum: Recruitment Genius: This is a rare opportunity for ...

Day In a Page

Surrounded by high-rise flats is a little house filled with Lebanon’s history - clocks, rifles, frogmen’s uniforms and colonial helmets

Clocks, rifles, swords, frogmen’s uniforms

Surrounded by high-rise flats is a little house filled with Lebanon’s history
Return to Gaza: Four months on, the wounds left by Israel's bombardment have not yet healed

Four months after the bombardment, Gaza’s wounds are yet to heal

Kim Sengupta is reunited with a man whose plight mirrors the suffering of the Palestinian people
Gastric surgery: Is it really the answer to the UK's obesity epidemic?

Is gastric surgery really the answer to the UK's obesity epidemic?

Critics argue that it’s crazy to operate on healthy people just to stop them eating
Homeless Veterans appeal: Christmas charity auction Part 2 - now LIVE

Homeless Veterans appeal: Christmas charity auction

Bid on original art, or trips of a lifetime to Africa or the 'Corrie' set, and help Homeless Veterans
Pantomime rings the changes to welcome autistic theatre-goers

Autism-friendly theatre

Pantomime leads the pack in quest to welcome all
The week Hollywood got scared and had to grow up a bit

The week Hollywood got scared and had to grow up a bit

Sony suffered a chorus of disapproval after it withdrew 'The Interview', but it's not too late for it to take a stand, says Joan Smith
From Widow Twankey to Mother Goose, how do the men who play panto dames get themselves ready for the performance of a lifetime?

Panto dames: before and after

From Widow Twankey to Mother Goose, how do the men who play panto dames get themselves ready for the performance of a lifetime?
Thirties murder mystery novel is surprise runaway Christmas hit

Thirties murder mystery novel is surprise runaway Christmas hit

Booksellers say readers are turning away from dark modern thrillers and back to the golden age of crime writing
Anne-Marie Huby: 'Charities deserve the best,' says founder of JustGiving

Anne-Marie Huby: 'Charities deserve the best'

Ten million of us have used the JustGiving website to donate to good causes. Its co-founder says that being dynamic is as important as being kind
The botanist who hunts for giant trees at Kew Gardens

The man who hunts giants

A Kew Gardens botanist has found 25 new large tree species - and he's sure there are more out there
The 12 ways of Christmas: Spare a thought for those who will be working to keep others safe during the festive season

The 12 ways of Christmas

We speak to a dozen people who will be working to keep others safe, happy and healthy over the holidays
Birdwatching men have a lot in common with their feathered friends, new study shows

The male exhibits strange behaviour

A new study shows that birdwatching men have a lot in common with their feathered friends...
Diaries of Evelyn Waugh, Virginia Woolf and Noël Coward reveal how they coped with the December blues

Famous diaries: Christmas week in history

Noël Coward parties into the night, Alan Clark bemoans the cost of servants, Evelyn Waugh ponders his drinking…
From noble to narky, the fall of the open letter

From noble to narky, the fall of the open letter

The great tradition of St Paul and Zola reached its nadir with a hungry worker's rant to Russell Brand, says DJ Taylor
A Christmas ghost story by Alison Moore: A prodigal daughter has a breakthrough

A Christmas ghost story by Alison Moore

The story was published earlier this month in 'Poor Souls' Light: Seven Curious Tales'