A study released on Wednesday confirmed that a newly found planet in outlying region of our solar system is actually bigger than Pluto, bolstering the claim that a tenth planet orbits the Sun.

The planet, named 2003 UB313, was first discovered by Mike Brown, a professor of planetary science at the California Institute of Technology. Like Pluto, it is an icy body in the so-called Kuiper Belt that exists beyond Neptune. It is the most distant object ever seen in the solar system.

Announcing his finding in last July, Brown believed this planet is larger than Pluto, which astronomers regarded as the 9th planet in our solar system. Brown insisted the planet should be defined as the 10th planet of the Sun, but astronomers are still debating around this advice.

Now, Brown has found supporters from Germany. Astronomers at the Bonn University said they determined the planet's diameter of about 3,000 km by measuring its thermal emission.

Thus, 2003 UB313 is 700 km larger than Pluto, and thereby becomes the largest solar system object found since the discovery of Neptune in 1846, the astronomers said in the Feb. 2 issue of the journal Nature.

It is a member of a ring of some 100,000 objects on the outskirts of the solar system, beyond Neptune at distances over 4 billion km from the Sun, over 30 times the distance between Earth and Sun. The objects in this "Kuiper belt" circle the Sun in stable orbits with periods of about 300 years, they reported.

Astronomers have found small planetary objects beyond the orbits of Neptune and Pluto since 1992, confirming the prediction that a belt of smaller planetary objects beyond Neptune exists. This so-called Kuiper Belt contains objects left from the formation of our planetary system some 4.5 billion years ago.

The Bonn group measured the heat radiation of the planet at a wavelength of 1.2 mm, where reflected sunlight is negligible and the object brightness only depends on the surface temperature and the object size.

"Since UB313 is decidedly larger than Pluto," said Frank Bertoldi, lead investigator of the study, "it is now increasingly hard to justify calling Pluto a planet if UB313 is not also given this status."

"The discovery of a solar system object larger than Pluto is very exciting," said Wilhelm Altenhoff, another researcher in the German group.

"It tells us that Pluto, which should properly also be counted to the Kuiper Belt, is not such an unusual object," he noted in a statement.

Source: Xinhua