Frozen world beyond Pluto's orbit is largest find in 72 years

By ANDREW BRIDGES
AP Science Writer

LOS ANGELES (AP) Astronomers announced Monday they have discovered an icy world 800 miles across, the biggest solar system find since Pluto was first spied in 1930.

The object is about one-tenth the diameter of Earth and orbits the sun once every 288 years at a distance of 4 billion miles 1 billion miles farther out than Pluto. Astronomers do not consider it a planet, but one of the largest of billions of objects in a swarm of primordial material that orbits the sun beyond Neptune.

The object, provisionally dubbed Quaoar (pronounced kwah-o-wahr), a creation force in Southern California Indian mythology, is only half the size of Pluto, which some astronomers believe should never have been called a planet.

The Quaoar is ``about the size of all the asteroids put together, so this thing is really quite big,'' said planetary astronomer Michael Brown, of the California Institute of Technology in Pasadena.

Brown and postdoctoral scholar Chadwick Trujillo unveiled their discovery Monday in Birmingham, Ala., at a meeting of the American Astronomical Society's division of planetary sciences.

The two used a telescope at the Palomar Observatory near San Diego to discover Quaoar in images taken June 4. Follow-up observations with the Hubble Space Telescope confirmed its size.

Archival research showed Quaoar was imaged as early as 1982, but never noticed, Brown said. He and Trujillo pored over the older images to help pin down the circular path it travels around the sun.

``It could easily have been detected 20 years ago, but it wasn't,'' Brown said.

Quaoar is the latest large object to be found in the solar system's Kuiper Belt. The belt contains frozen, fossil remnants of the swirling disk of debris that clumped together to form the solar system roughly 5 billion years ago. It is also believed to be the source of some comets.

The belt contains as many as 10 billion objects at least one mile across; astronomers estimate five to 10 of those are jumbo-sized like Quaoar.

``This new discovery fits right in with our expectation that there should be a handful or two of objects as large as Pluto,'' said astronomer David Jewitt of the University of Hawaii. Jewitt, with then-colleague Jane Luu, discovered the first Kuiper Belt object just a decade ago.

As larger and larger Kuiper Belt objects turn up, the case for Pluto as a planet weakens, astronomers said. Pluto lies within the Kuiper Belt and is considered by many merely the largest of the bunch, and not a planet in its own right.

``It's pretty clear, if we discovered Pluto today, knowing what we know about other objects in the Kuiper Belt, we wouldn't even consider it a planet,'' Brown said.

Astronomers expect yet-undiscovered Kuiper Belt objects may rival even Pluto.

``An observation like this just confirms that ... we may discover Kuiper Belt objects bigger than Pluto,'' said Frank Summers, an astrophysicist at the Space Telescope Science Institute in Baltimore.

The National Aeronautics and Space Administration is considering launching a spacecraft to explore Pluto, its moon, Charon, and at least one Kuiper Belt object, but whether it will be funded remains unclear. The New Horizons mission could launch as early as 2006, and would take about a decade to reach Pluto.

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On the Net:

Kuiper Belt: http://www.ifa.hawaii.edu/faculty/jewitt/kb.html

New Horizons: http://pluto.jhuapl.edu/

(Copyright 2002 by The Associated Press. All Rights Reserved.)