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Discovery of a Large Kuiper Belt Object with an Unusual Orbit
Discovery of a Large Kuiper Belt Object with an Unusual Orbit
14 Dec 2005
(Source: University of Hawaii)

A team of astronomers working in Canada, France and the United States have discovered an unusual small body orbiting the Sun beyond Neptune, in the region astronomers call the Kuiper belt.

This new object is twice as far from the Sun as Neptune and is roughly half the size of Pluto. The body's highly unusual orbit is difficult to explain using previous theories of the formation of the outer Solar System. Currently 58 astronomical units from the Sun (1 astronomical unit, or AU, is the distance between the Earth and the Sun), the new object never approaches closer than 50 AU, because its orbit is close to circular.

Almost all Kuiper belt objects discovered beyond Neptune are between 30 AU and 50 AU away. Beyond 50 AU, the main Kuiper belt appears to end, and what few objects have been discovered beyond this distance have all been on very high eccentricity (non-circular) orbits. Most of these high-eccentricity orbits are the result of Neptune "flinging" the object outward by a gravitational slingshot. However, because this new object does not approach closer than 50 AU, a different theory is needed to explain its orbit.

Complicating the problem, the object's orbit also has an extreme tilt, being inclined (tilted) at 47 degrees to the rest of the Solar System. The Discovery and Follow-up The object, which received the official designation 2004 XR 190 in the International Astronomical Union's official announcement, was discovered during routine operation of the Canada-France Ecliptic Plane Survey (CFEPS) running as part of the Legacy Survey on the Canada France Hawaii Telescope.

For now, the discoverers are using the temporary nickname "Buffy" to identify the new object, although they have proposed a different official name in keeping with normal procedures for naming such objects. Buffy was extracted from the mountain of Legacy Survey data (about 50 gigabytes per hour of operation) by powerful computers combing through the telescopic images and producing hundreds of candidates.

Astronomers then sift through the candidates to identify the distant comets. Astronomer Lynne Allen of the University of British Columbia was the first to lay eyes on the new object, as she completed the initial identification in the course of processing CFEPS data from December 2004. "It was quite bright compared to the usual Kuiper belt objects we find", said Dr. Allen, "but what was more interesting was how far away it was." The object's brightness implies it is likely between 500 and 1000 kilometers (300 to 600 miles) in diameter.

Buffy is thus a very large Kuiper belt object, but about half a dozen are larger. "We immediately realized that the object was about twice as far as Neptune from the Sun and that its orbit was potentially nearly circular," said UBC professor Brett Gladman, who noticed the unusual nature of the object when determining its orbit, "but further observations were required." One to two years of observations of a Kuiper belt object are required before their orbits can be precisely measured.

The first additional observations of Buffy came in October 2005 when Gladman and Phil Nicholson of Cornell University used the Hale 5-meter telescope to re-observe the object. Measurement of Buffy's new position proved that the orbit was not only extremely tilted, inclined (tilted) at 47 degrees to the plane of the planetary system (essentially tying the record for a Kuiper belt object) but confirmed that Buffy was unlike any other previously-known object because it was on a nearly circular orbit while at a very large distance.

More measurements of Buffy's position on images from telescopes at Kitt Peak National Observatories in Arizona by team members Joel Parker (Southwest Research Institute), as well as JJ Kavelaars (National Research Council of Canada, Herzberg Institute of Astrophysics) and Wes Fraser (University of Victoria), through November 2005 refined the estimate for Buffy's closest approach to the Sun. Additional observations, to further confirm the orbit, where then provided by the CFHT Legacy Survey project. Astronomers will need to wait until February 2006 to measure the fine details of the Buffy's orbit. The team have reported their find to the Minor Planet Center, the clearinghouse for astronomical measurements of new minor planets. "To find the first known object with a nearly circular orbit beyond 50 AU is indeed intriguing," reacted Brian Marsden, director of the MPC.

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Last Updated: 13 Jun 2010