Web Extra Tuesday, March 16, 2004

Sedna: Newly sighted planetoid in the solar system

At the edge of the solar system, astronomers have unexpectedly sighted an object slightly smaller and farther from the Sun than Pluto — not quite another planet, but not a temporary visitor either. Announcing the discovery yesterday, a team of scientists led by Michael Brown of Caltech in Pasadena, Calif., said the object is a planetoid — an asteroid that resembles a planetary body.

Artist's rendering compares the three smallest and most distant planetoids in the solar system — Quaoar, the newly sighted Sedna and Pluto — with Earth and the Moon. Image courtesy of Caltech/NASA.

The discoverers have proposed naming the body Sedna, after an Inuit goddess of the sea. Its relatively erratic orbit takes 10,500 years, and at its farthest point, it is 130 billion kilometers away from the Sun. (Earth is about 150 million kilometers from the Sun, and Pluto, almost 6 billion kilometers away.)

Brown's team has hypothesized that the small red planetoid may be the first object ever sighted from the Oort Cloud. The large assemblage of comets sits much farther outside the solar system than the planetoid's orbit. Other scientists noted the object could be a captured part of the Kuiper Belt, a disk of icy comets near Neptune's orbit. For more information, follow the links below.

NASA article on Sedna
Sedna home page of principal investigator Michael Brown of Caltech
Link to movie of Sedna's orbit from Caltech (large file: 15 M)
A comparison of orbits in the Solar System (courtesy of Caltech/NASA)

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