Planet-hunters find bonanza of new solar systems

By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters) - Planet-seekers who have spotted 28 new planets orbiting other stars in the past year say Earth's solar system is far from unique and there could be billions of habitable planets.

The most recent planet discoveries bring the number of known exoplanets -- planets outside our solar system -- to 236, the researchers told a meeting of the American Astronomical Society in Honolulu on Monday.

"We are beginning to see that our home is not a rarity in the universe," said Geoffrey Marcy, a professor of astronomy at the University of California Berkeley, who led the team.

"We are easily able to detect giant planets like Jupiter and Saturn around other stars. Most orbit far from the star like our own Jupiter and Saturn orbit from the sun," Marcy said in a telephone interview.

"It's a common structure among planetary systems."

New techniques allow astronomers to detect planets that are not enormous although Earth-sized objects cannot yet be seen, said the researchers, who have posted details of their findings on the Internet at exoplanets.org.

Four of the systems also have multiple planets, like Earth's own with its sun, eight planets (Pluto was demoted from planet status) and smaller orbiting objects.

"We are finding that most stars have not just one planet but when we find one there is a second or a third or a fourth," Marcy said.