'Super-Earth' Planets Discovered

Nearby stars probably abound with planets only slightly larger than our own, an international astronomy team suggested Monday as it reported the discovery of 45 of these "super-Earth" planets.

All of the planets, including a solar system of three super-Earths reported by team leader Michel Mayor of Switzerland's University of Geneva Observatory, orbit too close to their stars to harbor life. Their surface temperatures exceed Mercury's in our solar system. Mercury has a mean temperature of 354 degrees.

"If you are considering life on these planets, forget it," says Mayor's colleague, astronomer Didier Queloz, a co-author on two studies detailing the discoveries submitted to the journal Astronomy and Astrophysics. "But what is exciting is that we can say about one-third of stars have these kind of low-mass planets."

Since Mayor announced the first discovery of a planet outside our solar system in 1995, astronomers have gone on to document about 300 such planets, including the latest ones, orbiting nearby stars.

Most are giant gas planets as big or bigger than Saturn and Jupiter, but lately astronomers have turned up more planets close to Earth in size.

"Probably the true abundance of these planets is even larger," says Notre Dame astronomer David Bennett, who attended Mayor's presentation in Nantes, France. Bennett announced a similar super-Earth discovery this month, and his planet was too cold for life.

The latest discoveries include a solar system of three planets orbiting the sunlike star HD 40307 about 42 light-years away. (One light-year is about 5.9 trillion miles.) Planets weigh 4.2, 6.7, and 9.4 times as much as Earth and complete their orbits in less than 21 days.