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Our corner of the galaxy got a little stranger this week with the discovery of Sedna, the most distant object ever spotted in the solar system. Now astronomers are puzzling over how it got there.
The most intriguing idea is that there might be another world as big as Earth, a gravitational bully lurking in some unexplored corner of the solar system.
Here's the problem: Scientists can't figure out how Sedna, which is about three-fourths as big as Pluto, came to have such a strange orbit around the Sun. Sedna's path is highly elliptic. It ranges from 76 astronomical units (AU) when it is closest to the Sun to 1,000 AU when it is farthest. One AU is the distance from Earth to the Sun.
"How on Earth could anything get into an orbit like that," wonders astronomer Brian Marsden. He suggests another sort of Earth might have had something to do with putting Sedna on its current, odd course.
Snowball Earth Twin?
Michael Brown, the astronomer at California Institute of Technology who led the discovery of Sedna, said the most likely scenario involves the Sun having been born in a star cluster, and several stars that were then closer to the solar system -- still more than 10,000 AU away -- were responsible for ejecting objects like Sedna.
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