March 17, 2004  
Volume 97, Issue 87  

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Planetoid discovered

By Christopher Smeenk
Gazette Staff

A group of American scientists announced Monday the discovery of the farthest known object in the solar system.

The object is classified as a planetoid and was named Sedna, after the Inuit goddess of the sea. Peter Brown, professor of physics and astronomy at Western, described Sedna as “a gigantic icy comet or moon.” Because Sedna is too small to be considered a planet, it is labelled a planetoid, he added.

“Sedna is unusual in a couple of ways,” he said. “One, its size is greater than anything observed in that region to date. Two, its orbit is considerably larger than any of the other planets.”

Michael Brown, an astronomy researcher at the California Institute of Technology, led the team that discovered Sedna. He described himself as being “shocked” at finding the planetoid. “This is the most distant thing ever seen in the solar system,” he said. “We just didn’t expect to find anything this far away.”

He added that Sedna is currently three times farther from the sun than Pluto. “We could only just barely see it — 100 years in the past or future it would be impossible to see,” he said.

At approximately 65 per cent the size of Pluto, Sedna is not large enough to meet planet standards. “There is no good definition of what is or is not a planet,” he said.

“Our new definition is that to be a planet, you must be considerably more massive than the things in your vicinity,” he said, adding by this standard, even Pluto would not be considered large enough.

Peter Brown noted that Sedna follows an “extreme elliptical orbit.” He said it reaches a maximum distance of 130 billion kilometres from the sun, or 1,000 times the average distance from the Earth to the sun. At perihelion (the closest a planet gets to its sun), Brown said Sedna is 90 times the distance between the Earth and sun.

He also said Sedna is suspected to belong to one of two possible classes of celestial objects: The Kuiper Belt, a disc of objects beyond Pluto with a roughly circular orbit of the sun, or the Oort cloud, a collection of comets in the distant reaches of the solar system.

The planetoid’s strange elliptical orbit may mean it belongs to the Oort cloud. If so, Peter Brown noted that Sedna will be the first observational evidence of the Oort belt which has only been theoretically postulated until now.

“It’s a golden age for astronomy right now,” said Shantanu Basu, professor of astronomy at Western. “It’s really the technology that is leading the research right now,” he said, pointing to telescopes currently under construction that range up to 50 metres in diameter.



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