The universe is looking increasingly crowded as scientists announced the first proof twin stars can host multiple planets - boosting their search for a planet that could support life.

"We're seeing more and more planets in more and more situations," Jerome Orosz, an astronomer at San Diego State University, told AFP.

"We're almost to the point where you look at a star and say why doesn't this have a planet?" he added.

Orosz is part of a team that has observed at least two planets orbiting around a pair of stars that are also orbiting each other.


It is a potentially chaotic arrangement - with shifting gravity depending on where the stars are - that scientists were not sure was possible.

"After a star forms, it's got a little bit of leftover material," Orosz explained, "which eventually forms the Earth and the planets."

"The question was, if you put the disk and debris around a binary (star), would it survive long enough to form planets? And the answer is yes."

The newly discovered planets were found around Kepler-47, a Sun-sized orb paired with another about a third as big.

The inner planet, Kepler-47b, orbits the pair of stars in less than 50 days. Although it cannot be viewed directly, scientists believe the destruction of methane in Kepler-47b's super-heated atmosphere might lead to a thick haze that could blanket the planet.

The outer planet, Kepler-47c, orbits the star every 303 days, placing it in the so-called "habitable zone," the region in a planetary system where liquid water might exist on the surface of a planet. While not a world hospitable for life, Kepler-47c is thought to be a gaseous giant slightly larger than Neptune, where an atmosphere of thick bright water-vapour clouds might exist.

NASA's Kepler telescope - searching through the universe for as many worlds as it can find - has already found bodies at four other twin stars.

But this is the first time astronomers have proof of more than one planet at a time.

And just maybe there is a third planet in there as well, Orosz said, though they still need more data.

Kepler-47c is of particular interest, as it is another step towards finding an Earth-size planet within the habitable zone.

"Now we can find planets in these sorts of orbits. So the next step is to look for smaller and smaller bodies," Orosz explained, something that becomes easier as more data accumulates.

"If you go out at night and look at the sky, roughly half the stars you see are binary stars," Orosz said.

"So the fact that you can find planets in the habitable zone of binary stars means you have lot more real estate" for potential life.

The findings have been published in the journal Science.

"Unlike our sun, many stars are part of multiple-star systems where two or more stars orbit one another. The question always has been - do they have planets and planetary systems? This Kepler discovery proves that they do," said William Borucki, Kepler, mission principal investigator at NASA's Ames Research Center in Moffett Field, California.

"In our search for habitable planets, we have found more opportunities for life to exist."

- AFP, Herald Online