Astronomers who have spotted 28 new planets orbiting other stars say Earth's solar system is far from unique and there could be billions of habitable planets.
The planet orbiting the star Gliese 436 has a diameter abut four times that of Earth and is more than 20 times heavier than Earth. The planet's atmosphere is probably composed of hydrogen and helium
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 this week.
"We are beginning to see that our home is not a rarity in the universe," says Geoffrey Marcy, a professor of astronomy at the
University of California, Berkeley, who led the team.
The 28 planets are among 37 new objects - each orbiting a star, but smaller than it - discovered by the teams in the past year.
"The ... attribute which really has us the most excited is this new planet which we found three years ago," Marcy says.
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