Originally created 03/16/04

Astronomers discover distant planetoid



LOS ANGELES -- A frozen world found more than 8 billion miles from Earth is believed to be the farthest known object within our solar system, scientists announced Monday.

The discovery of red and shiny Sedna, a "planetoid" of rock and ice between 800 miles and 1,100 miles in diameter, or about three-quarters the size of Pluto, was announced by Mike Brown, an astronomer at the California Institute of Technology who led the NASA-funded team that found it.

The find "opens a new fossil window into the solar system," he told a teleconference with journalists.

Named for the Inuit goddess who created the sea creatures of the Arctic, Sedna lies more than three times farther from the sun than Pluto. It was discovered in November.

Sedna is the largest object found orbiting the sun since the discovery of Pluto, the ninth planet, in 1930. It trumps in size another object, called Quaoar, discovered by the same team in 2002.

"We think this is one of the most primordial objects in the solar system," Brown said. "Very little has happened to this object since the beginning of the solar system."

Sedna is so far out that from its distance the sun could be completely blocked out with the head of a pin, he said.

Brown would not classify Sedna as a planet. He said planets are considerably more massive than any other object in a given location, and researchers predict that other, more massive objects will be found near Sedna.

"We think it's not reasonable to call Sedna a planet," said Brown, who noted that astronomers don't have an official definition of what constitutes a planet and who does not even consider Pluto a planet.

Brown and his colleagues believe Sedna to be the first known member of the long-hyphothesized Oort Cloud, a repository of some of the comets that swoop past Earth.

The orbit of Sedna suggests that our solar system formed in a cluster of stars that no longer are nearby, Brown said. He cautioned that more evidence would be needed to prove that, though.

The scientists estimate the temperature on Sedna never rises above 400 degrees below zero Fahrenheit, making it the coldest known body in the solar system.

Sedna follows a highly elliptical path around the sun, a circuit that it takes 10,500 years to complete. It is relatively close to the sun now, but loops out as far as 84 billion miles from the sun at its farthest point, or 900 times the distance between the sun and Earth.

Brown and Chad Trujillo, of the Gemini Observatory in Hawaii, and David Rabinowitz, of Yale University, discovered Sedna on Nov. 14, using a 48-inch telescope at Caltech's Palomar Observatory east of San Diego.

Within days, other astronomers around the world trained their telescopes, including the recently launched Spitzer Space Telescope, on the object.

The team also have indirect evidence a tiny moon may trail Sedna, which is redder than all other known solar system bodies except Mars.

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