The universe is looking increasingly crowded as scientists Tuesday 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's a potentially chaotic arrangement -- with shifting gravity depending on where the stars are -- that scientists weren't 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.

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's a third planet in there as well, Orosz said, though they still need more data.

The planets are gas giants, around the size of Neptune. But these two are orbiting very close to their suns.

In fact, the outer planet is hanging out within that sweet spot scientists call the "habitable zone" -- not too close and hot, not too far and cold.

That's a first, too, and an exciting one, because it's another step towards finding an Earth-size planet within that zone, somewhere out there.

"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.

With Orosz as lead author, the team presented its findings in the magazine "Science."