The object has been named Sedna after the Inuit goddess of the sea, and is thought to be the coldest body in the solar system, and the most distant object orbiting the sun.

Researchers at the California Institute of Technology discovered the object in November 2003.

While they consider it the most important discovery in our solar system in over 70 years, they are not sure that Sedna amounts to a planet.

"We think it's not reasonable to call Sedna a planet, but we think it's not reasonable to call Pluto a planet," said Michael Brown, an astronomer at the California Institute of Technology, Pasadena, California.

"It is not massive enough."

There is some debate about what exactly constitutes a planet, and not all astronomers agree that Pluto deserves to be considered as a planet.

Sedna is roughly half the size of the Earth's moon, or two-thirds the size of the planet Pluto and more reddish in appearance than any other planet except Mars.

It is an estimated 13 billion kilometers (eight billion miles) from earth.

"The Sun appears so small from that distance that you could completely block it out with the head of a pin," said Brown, who was speaking at NASA's Jet Propulsion Laboratory in Pasadena, California.

Brown said temperatures on Sedna probably never rise above -240 degrees Celsius (-400 F) and its elliptical rotation around the sun takes an estimated 10,500 years.

Its orbit takes Sedna up to 130 billion kilometers (81 billion miles) from the sun, or 900 times the distance from the earth to the sun.

Brown and his colleagues identified Sedna on November 14, 2003, using a telescope at Caltech's Palomar Observatory east of San Diego, California.

SPACE.WIRE