Pluto has new, far out peer

Scientists have recently discovered a planetary body beyond Pluto, pictured above with its moon Charon, is bigger than expected

(CNN) -- The unexpected size of a recently discovered body beyond Pluto has scientists wondering if even larger objects lurk in the depths of the solar system.

After Pluto and its moon Charon, Varuna has been identified as the largest known body in the Kuiper Belt, a ring composed of more than 70,000 cold, dark and slow-moving objects beyond the orbit of Neptune, scientists announced Thursday.

Using telescopes on a mountain peak in Hawaii, astronomers determined that Varuna has a diameter of about 900 km (550 miles), compared to about 2,200 km (1,350 miles) for Pluto and 1,200 km (750 miles) for Charon.

Discovered in November, Varuna closes the gap between Pluto and the previously largest known Kuiper-Belt object, which is around 600 km (350 miles) in diameter, said astronomer Steve Tegler of Northern Arizona University.

RESOURCE Click here to compare Pluto, Varuna and other ice balls in the Kuiper Belt

"Pluto and Charon are not so unique in size now. Perhaps more Pluto-sized objects or even larger objects remain undiscovered in the outer reaches of the solar system."

Varuna could be the first of many such discoveries, predicted Tegler and a colleague in an editorial entitled 'Almost Planet X' in the May 24 issue of the Nature.

The essay accompanied an article detailing the new Varuna findings, written by lead scientist David Jewitt of the Institute for Astronomy in Hawaii and two associates.

The trio found that Varuna reflects about 7 percent of the sunlight that strikes its surface, considerably more than most identified objects in the Kuiper Belt.

"The higher than guessed albedo (reflectivity) may be due to the presence of some ice on the surface, but nothing like as much as Pluto can command," said Brian Marsden of the Harvard-Smithsonian Observatory.

Varuna is much darker than Pluto, a frosty world with a seasonal atmosphere that bounces back about 60 percent of the solar light that reaches it.

Some astronomers consider the new revelations vindication of the work of Clyde Tombaugh, who in 1930 spotted Pluto during a search for the elusive Planet X. Unconvinced that his icy find was his intended quarry, he kept looking for other sizable, distant objects.

More Kuiper Belt surprises may await astronomers after space shuttle astronauts deploy an infrared telescope facility in 2002. The instrument is expected to provide more precise measurements of objects in the distant solar system.