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Deep space world rivals Pluto moon in size

Kuiper Belt object
Two exposures from a telescope in Chile were combined to show the movement of the new Kuiper Belt discovery, which appears as a pair of red dots  

(CNN) -- Astronomers have discovered a protoplanetary piece of ice beyond the orbit of Neptune, bolstering speculation that even bigger bodies lurk in the frigid recesses of the solar system.

The object, identified using numerous powerful telescopes across the world, is considered the largest known object in an icy ring beyond the planets composed of primordial comets.

"This object is intrinsically the brightest Kuiper Belt Object (KBO) found so far," said Robert Millis, director of the Lowell Observatory and leader of the discovery team.

And brightness is a reflection of size. Because of the distance, darkness and diminutiveness of KBOs, astronomers must calculate their diameters based on how much light they reflect, an inexact science at best.

Space exploration  

Using traditional assumptions, researchers speculate that the new KBO, known as 2001 KX76, could be larger than 788 miles (1,270 km). In contrast, Pluto's moon Charon has an estimated diameter of 744 miles (1,200 km).

But the object could be smaller if it reflects more light than anticipated. One alternative measurement places the diameter at 595 miles (960 km).

Regardless, 2001 KX76 boasts an impressive girth. The previously largest known KBO, Varuna, discovered earlier this year, has an estimated diameter of 559 miles (900 km).

The new KBO heavyweight is slightly more than 4 billion miles (6.4 billion km) from the sun. It could be in an orbital resonance with Neptune, completing three orbits around the sun in the time it takes gas planet to go four times around the sun.

The discovery was exciting, Millis said, because it shows that many bodies remain to be discovered in the Kuiper Belt.

"We have every reason to believe that objects ranging up to planets as large or larger than Pluto are out there waiting to be found," he said in a statement this week announcing the discovery.

Since 1992, astronomers have identified more than 400 KBOs, thought to be remnants from the formation of the solar system. Tens of thousands are thought to remain hidden. Pluto, while historically considered a planet, most likely is a large KBO, most modern astronomers agree.

The Space Infrared Telescope Facility (SIRTF), expected to launch in 2002, should provide much more precise measurements of KBO diameters.

The latest discovery was made by the Deep Ecliptic Survey Team, which is composed of scientists from the Lowell Observatory in Flagstaff, Arizona, and the Massachusetts Institute of Technology, in Cambridge, Massachusetts.

• Pluto-Planet Profile
• Pluto-Kuiper Express

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