Oddball object circles sun beyond Neptune

  • World
  • Friday, 16 Dec 2005

By Jim Wolf

WASHINGTON (Reuters) - A distant object named Buffy has been spotted circling the sun far beyond Neptune in a strange tilted orbit that is making some astronomers question how the outer reaches of the solar system formed. 

Officially called 2004 XR 190 by the International Astronomical Union but code-named Buffy, the object is now about 58 times as far from the sun as Earth, and twice as far from the sun as Neptune. 

At this distance from the heart of the planetary system, Buffy is a considered a Kuiper Belt object, but an odd one, astronomers working in Canada, France and the United States said in a statement on Tuesday. 

The Kuiper Belt is a ring of space objects that may be remnants from the early solar system. Most of these objects orbit the sun between 30 and 50 times the distance that Earth orbits. The distance from Earth to the sun -- 150 million km -- is known as one astronomical unit. 

Most Kuiper Belt objects are contained in this thick swath of space, and most have elliptical orbits, which means they get much closer to Neptune during parts of their orbits. They generally orbit in the same plane as most of the planets and other solar system objects. 

But Buffy's circular track means it stays beyond the 50 astronomical unit range for its entire orbit, never getting much closer than 52 astronomical units, or AU, and sometimes swinging out to 62 AU. 

The only other known object that never gets within the 50 AU boundary is Sedna, which flings out to 900 AU and swoops in to 76 AU. But Sedna's orbit is typically elliptical, while Buffy goes around in a near-perfect circle. 

And Buffy's orbit is tilted at a 47 degree angle from the rest of the solar system. 

The highly eccentric orbits of the other Kuiper Belt objects are thought to be the result of being flung outward in a slingshot effect by Neptune's gravity. But Buffy's orbit does not follow that pattern. 

More information and images are available online at http://www.cfht.hawaii.edu/. 

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