When astronomers mike Brown, David Rabino-witz and Chad Trujillo spotted an unfamiliar object in space last November, they weren't sure what it was. "It took us a few weeks of continuing to see this object until we were really convinced we had stumbled onto something big," says Brown, who led the team and teaches astronomy at the California Institute of Technology, in Pasadena.
On March 15, the scientists announced that they had discovered a frozen, planetlike object about 8 billion miles from Earth. It is the most distant object known to orbit the Sun and the largest one found since Pluto was discovered, in 1930. The astronomers named it Sedna, after the Inuit goddess of the sea. Sedna could be larger than Quaoar (kwah-oh-ar), a giant ball of ice that the same team discovered in 2002.
With a diameter of 800 to 1,100 miles, Sedna is about three-quarters the size of Pluto, the smallest and usually farthest planet from the Sun. It takes Pluto 248 years to travel around the Sun. Sedna takes 10,500 years! The astronomers were able to spot Sedna because the red object is now at one of its closest points to Earth.
To be labeled a planet, an object in orbit around a sun must be considerably larger than any other object near it. Astronomers are calling the half-ice, half-rock Sedna a planetoid. "There will be many, many more of these objects found over the next decade," Brown predicts. "And it will turn out that Sedna is not the most massive object in its orbit out there."
Sedna and Quaoar have caused a big stir. "Even small objects are significant," Rabinowitz told TFK. "They tell us that there's more solar system out there than we have ever imagined."