By BBC News Online science editor Dr David Whitehouse
Astronomers
have found a new member of the Solar System that orbits the Sun
beyond Neptune.
It could be
half the diameter of Pluto, which in 1930 was the last planet
to be discovered.
The object,
temporarily named 2000 WR106, was spotted on 28 November. It was
picked up by the University of Arizona's Spacewatch team which
searches the sky for potentially hazardous objects.
Astronomers
say that after Pluto, 2000 WR106 is the brightest object of its
kind in this particular region of the Solar System.
Data uncertainties
The object
was imaged by the Spacewatch survey telescope. After 12 observations
made over three days, researchers reported the existence of the
body to the International Astronomical Union's Minor Planet Center
(MPC) in Cambridge, Massachusetts, who issued an alert.
Using the
available data, the MPC calculated that the new object was 43
times further from the Sun than the Earth - a distance of about
6.5 billion kilometres (4bn miles). This puts it in a class known
as the Trans-Neptunian Objects.
At the moment,
astronomers say it is not possible to make a definitive statement
about the object's diameter. This is because of uncertainties
about its reflectivity.
However, if
it is similar to other Trans-Neptunian Objects, it could be between
650 and 1,300 km (400 - 800 miles) across.
Asteroids
and comets
By comparison,
Pluto has a diameter of 2,370 km (1,470 miles).
Further observations
of the object's position will be made in the coming weeks and
months to improve knowledge of its orbital parameters and physical
properties.
Astronomers
will want to obtain a spectrum so that they can determine of what
materials the body is made.
The Spacewatch
Project is a search for new objects in space throughout the whole
Solar System. It was started in 1980 by Tom Gehrels and Robert
McMillan at the Lunar and Planetary Laboratory of the University
of Arizona.
This project
is one several around the world that automatically scan the sky
for asteroids and comets.
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