Scientists Discover New Planet Bigger Than Pluto

Feb. 1, 2006 — -- Scientists today confirmed the existence of a 10th planet in our solar system.

For now, it appears only as a dot, moving ever so slowly across the sky.

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But from its movement and brightness, scientists can tell it is in a long, elliptical orbit -- more than 90 times farther from the sun than Earth is.

It is a frozen world -- more than 400 degrees below zero. It takes 560 years to circle the sun once.

"To think that you could actually find something in our own solar system bigger than anything that had been seen in 150 years, just is sort of an amazing prospect," said Michael Brown, professor of planetary astronomy at the California Institute of Technology.

Brown is the astronomer who headed the discovery team. He says that if other scientists agree, it's time to start rewriting the textbooks: The sun now has 10 planets.

"Suddenly there's an object the size of Pluto or bigger that's three times farther out there," he said. "That's sort of an amazing thought."

A second group of astronomers has decided that the new planet is probably quite a bit larger than Pluto. It's about 1,900 miles across, compared with 1,400 for Pluto.

So if Pluto is considered a planet, then this new one qualifies too.

ABC News' Ned Potter filed this report.