'Minor planet' found in obscure corner of solar system

PHOENIX, Arizona (Reuters) -- A University of Arizona astronomer has found an object in the outer reaches of the solar system that could be the second brightest and largest so-called "minor planet" in space, researchers said Monday.

Dubbed 2000 WR106, the large object visually plucked from the sky last week by astronomer Robert McMillan appears only to be outdone by Pluto when it comes to such objects located beyond Neptune's orbit, researchers said.

The discovery, spotted in a crowded star field in the northern Milky Way, is one-fourth to one-half the size of Pluto.

It measures roughly 330 miles (531 kms) to 750 miles (1,207 kms) in diameter and is 43 times further from the sun than Earth is.

It is believed to be bigger than Ceres, the largest known asteroid.

"I knew it had the chance to be very special when I saw it," said McMillan, principal investigator for the Spacewatch Project, a 20-year-program he co-founded that studies the solar system. "It's pretty gratifying to find something like this after all these years."

Such "minor planets" are classified by researchers in the field as Trans-Neptunian Objects, items that stretch beyond that planet. There have been 346 catalogued since the effort began in 1992, but few like 2000 WR106.

"The brighter the object, usually the bigger it is," said Brian Marsden, director of the International Astronomical Union's Minor Planet Center in Cambridge, Massachusetts. "If it's bright, it's big in this game. That's a good rule of thumb."

Marsden said the discovery may be an important step toward better understanding and helping chart the blueprint for the vastness of space.

It also could mean that there are other large objects to be found - perhaps even Pluto-sized objects - in the solar system in the years to come.

McMillan said he first saw the slow-moving object November 28 while glancing at the computer screen from real-time images captured from a telescope on Kitt Peak, near Tucson, Arizona. It was not detected by computer software.

He bounced from frame to frame until he was sure he may have seen something.

McMillan believes the bright object may have escaped astronomer's eyes because they do not tend to look in crowded places, preferring to search in better conditions.

"It's really like looking for lost keys under the street light," he said. "It's easier to look in places that are clearer, where things are more easily found."

The object was confirmed with 12 sightings over the next three days by McMillan and astronomer Jeffrey Larsen and reported to the planet center.

McMillan believes it will take up to two years of efforts by other researchers to determine the complete picture for the object known as 2000 WR106.

Copyright 2000 Reuters. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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