By Dr David Whitehouse
Science editor, BBC News website
Astronomers have found a large object in the Solar System's outer reaches. It is being hailed as "a great discovery".
The new object was discovered in the outer reaches of the Solar System
Details of the object are still sketchy. It never comes closer to the Sun than Neptune and spends most of its time much further out than Pluto.
It is one of the largest objects ever found in the outer Solar System and is almost certainly made of ice and rock.
It is at least 1,500km (930 miles) across and may be larger than Pluto, which is 2,274km (1,400 miles) across.
The uncertainty in estimates of its size is due to errors in its reflectivity.
It might be a large, dim object, or a smaller, brighter object. Whatever it is, astronomers consider it a major discovery.
In 2004 scientists discovered Sedna, a remote world that is 1,700 km across.
Two groups of scientists will be claiming the latest discovery.
It was picked up by astronomers of the Institute of Astrophysics in Andalusia as part of a survey of the outer solar system for new objects that they have been carrying out since 2002.
"We found a bright, slow moving object while checking some older images of our survey for Trans-Neptunian Objects," Jose-Luis Ortiz, one of the objects co-discoverers, told the BBC News website.
It was subsequently designated 2003 EL61.
However, American astronomers also appear to have detected it.
The same team that found Sedna have designated it K40506A after it was picked up by the Gemini telescope and one of the twin Keck telescopes in Hawaii.
They are due to present their findings at a conference in Cambridge in September.
Because the object is relatively bright, astronomers are frantically checking other observations that may have picked it up, particularly robotic sky surveys.