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Astronomers have discovered a satellite companion of a supercomet in the Kuiper Belt, the part of the solar system beyond the orbit of Neptune. Until now, Pluto, the outermost planet, was the only object in this region known to have a satellite. The finding supports some astronomers' contention that Pluto shouldn't be considered a planet.
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Dance partners. A comet beyond Neptune's orbit is circled by a newfound satellite.
CREDIT: CHRISTIAN VEILLET |
The discovery was serendipitous, says team leader Christian Veillet of the Canada-France-Hawaii Telescope (CFHT) in Mauna Kea, Hawaii. Still, the existence of binary Kuiper Belt Objects wasn't unexpected. Astronomers had already planned to search for them with the Hubble Space Telescope later this year. "I think that probably nobody really thought that you could actually see one from the ground on a medium-size telescope [such as Mauna Kea's 3.6-meter CFHT]," says Veillet.
The satellite is at least 40,000 kilometers from its parent object, a supercomet known as 1998 WR31 , the researchers announced 15 April in an International Astronomical Union circular. In the next few days, Veillet hopes to precisely determine the satellite's orbit, using old photographs of the pair. This will make it possible to calculate the mass of the comet and its satellite. And if the two objects occasionally pass in front of each other, as in an eclipse, the resulting brightness changes may be used to map large features on their surfaces.
The discovery suggests that the binary nature of Pluto isn't exceptional for its neighborhood. Indeed, such pairs are probably a fairly common result of collisions in the Kuiper Belt, notes Alan Stern of the Southwest Research Institute in Boulder, Colorado. That supports the popular view among astronomers that Pluto should be considered a Kuiper Belt Object, albeit a very large one. "Those who argue that Pluto is 'different' because it has a satellite need to think again," says Benny Peiser of Liverpool John Moores University, United Kingdom.
--GOVERT SCHILLING
Related sites
Discovery announcement by the International Astronomical Union
Christian Veillet's page on the discovery
General information on the Kuiper Belt
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