Half of stars orbited by planets

One star in two may host a family of orbiting planets, greatly boosting the chances of life beyond the earth, say scientists.

Data flooding in from the American space agency Nasa’s new Kepler space telescope has already revealed more than 1,200 possible worlds.

Of these, 54 lie within the “Goldilocks zone” - the orbital region just far enough from the parent star to allow perfect conditions for liquid surface water and possibly life.

Four or five are thought to be roughly the size of earth.

William Borucki, Kepler’s prinicipal investigator from Nasa’s Ames Research Centre in Moffett Field, California, said: “Right now for every two stars we’re seeing a planet or candidate planets. That’s wonderful.

“I am really delighted to find that we are seeing so many candidates. We’re seeing all sizes around all sorts of stars. There is a rich ocean out there for us to explore.”

The “candidate” planets have yet to undergo rigorous identity tests to confirm they really are other worlds.

This can take time as painstaking measurements are carried out using earth-based telescopes. But the scientists are confident the vast majority of objects they have identified are planets.

Dr Borucki and a group of colleagues spoke about Kepler’s discoveries at the annual meeting of the American Association for the Advancement of Science in Washington DC.

They told of a plethora of observations that had taken them by surprise.

Among them was Kepler 10b, a hot rocky planet with no atmosphere and lakes of liquid lava, Kepler 7b, an unusually bright hot “Jupiter” reflecting a lot of starlight, and Kepler 11, an entire solar system with six “gassy” planets all orbiting closer to their star than Mercury is to the Sun.

Kepler spots planets by measuring the miniscule dimming which occurs as they cross or “transit” the face of their star.

All the earth-sized candidate planets observed so far have orbited stars smaller and cooler than the sun. Scientists are eagerly awaiting new data expected next year which may reveal rocky planets like the earth around sun-like stars.

“There’s no reason to believe that what we’re finding now around the cool stars we won’t find around the hotter stars,” Dr Borucki said.