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
i100 In this video, the late actor Leonard Nimoy explains how he decided to use the gesture for his character
Arts and Entertainment
Secrets of JK Rowling's Harry Potter workings have been revealed in a new bibliography
arts + ents
Down-to-earth: Winstone isn't one for considering his 'legacy'
ebooksA special investigation by Andy McSmith
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating

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

iJobs Job Widget
iJobs General

Sauce Recruitment: Retail Planning Manager - Home Entertainment UK

salary equal to £40K pro-rata: Sauce Recruitment: Are you available to start a...

Ashdown Group: Front-End Developer - London - up to £40,000

£35000 - £40000 per annum: Ashdown Group: Creative Front-End Developer - Claph...

Recruitment Genius: Product Quality Assurance Technologist - Hardline & Electric

£18000 - £24000 per annum: Recruitment Genius: The role in this successful eco...

Ashdown Group: QA Tester - London - £30,000

£28000 - £30000 per annum: Ashdown Group: QA Tester - London - £30,000 QA Tes...

Day In a Page

HIV pill: Scientists hail discovery of 'game-changer' that cuts the risk of infection among gay men by 86%

Scientists hail daily pill that protects against HIV infection

Breakthrough in battle against global scourge – but will the NHS pay for it?
How we must adjust our lifestyles to nature: Welcome to the 'Anthropocene', the human epoch

Time to play God

Welcome to the 'Anthropocene', the human epoch where we may need to redefine nature itself
MacGyver returns, but with a difference: Handyman hero of classic 1980s TV series to be recast as a woman

MacGyver returns, but with a difference

Handyman hero of classic 1980s TV series to be recast as a woman
Tunnel renaissance: Why cities are hiding roads down in the ground

Tunnel renaissance

Why cities are hiding roads underground
'Backstreet Boys - Show 'Em What You're Made Of': An affectionate look at five middle-aged men

Boys to men

The Backstreet Boys might be middle-aged, married and have dodgy knees, but a heartfelt documentary reveals they’re not going gently into pop’s good night
Crufts 2015: Should foreign dogs be allowed to compete?

Crufts 2015

Should foreign dogs be allowed to compete?
10 best projectors

How to make your home cinema more cinematic: 10 best projectors

Want to recreate the big-screen experience in your sitting room? IndyBest sizes up gadgets to form your film-watching
Manchester City 1 Barcelona 2 player ratings: Luis Suarez? Lionel Messi? Joe Hart? Who was the star man?

Manchester City vs Barcelona player ratings

Luis Suarez? Lionel Messi? Joe Hart? Who was the star man at the Etihad?
Arsenal vs Monaco: Monaco - the making of Gunners' manager Arsene Wenger

Monaco: the making of Wenger

Jack Pitt-Brooke speaks to former players and learns the Frenchman’s man-management has always been one of his best skills
Cricket World Cup 2015: Chris Gayle - the West Indies' enigma lives up to his reputation

Chris Gayle: The West Indies' enigma

Some said the game's eternal rebel was washed up. As ever, he proved he writes the scripts by producing a blistering World Cup innings
In Ukraine a dark world of hybrid warfare and murky loyalties prevails

In Ukraine a dark world of hybrid warfare

This war in the shadows has been going on since the fall of Mr Yanukovych
'Birdman' and 'Bullets Over Broadway': Homage or plagiarism?

Homage or plagiarism?

'Birdman' shares much DNA with Woody Allen's 'Bullets Over Broadway'
Broadchurch ends as damp squib not even David Tennant can revive

A damp squib not even David Tennant can revive

Broadchurch, Series 2 finale, review
A Koi carp breeding pond, wall-mounted iPads and a bathroom with a 'wellness' shower: inside the mansion of Germany's 'Bishop of Bling'

Inside the mansion of Germany's 'Bishop of Bling'

A Koi carp breeding pond, wall-mounted iPads and a bathroom with a 'wellness' shower