Hunt for extrasolar planets turns to Earth-size worlds

BALTIMORE, Maryland (Reuters) -- Ten years after finding the first planet outside our solar system, scientists say they may be ready to move into a new phase of planetary exploration -- one that examines distant worlds for signs of Earth-like life.

So far, astronomers have discovered some 145 so-called extrasolar planets orbiting stars besides our sun. All are gas giants like Jupiter, thought to be inhospitable to life as it is known on Earth.

But some of the world's premier planet hunters indicated this could change in the next decade.

"Within a few years, we may be able to detect things like our own solar system," said Mario Livio, an astrophysicist at the Space Telescope Science Institute. That could help answer what he termed the most intriguing question in science today: is there intelligent life anywhere besides Earth?

"The capability of seeing, detecting, planets the size of the Earth is only now just coming into our grasp," said Jaymie Matthews, an astronomer at the University of British Columbia.

"I think we can look forward reasonably in the next decade to finding out are there Earth-size planets in Earth-like orbits going around every star," said Tim Brown of the National Center for Atmospheric Research. "We're going to have to wait a while to find out whether they have atmospheres."

Matthews, Livio and Brown were among scientists gathered last week for a symposium on a decade of research into extrasolar planets at the Space Telescope Science Institute in Baltimore, which deals with data gathered by the Hubble Space Telescope.

Since the first extrasolar planet was detected in 1995 around a star known as 51 Pegasi, astronomers have uncovered dozens by identifying stars that wobble because of the gravitational pull of planets around them. They have found others by watching for a very slight dimming of stars caused by the orbiting of planets.

Getting even a blurry image of an extrasolar planet has proven tricky. The closest astronomers have come is a picture of a fuzzy-looking red ball orbiting a brown dwarf 200 light-years from Earth. A light-year is about 6 trillion miles (10 trillion km), the distance light travels in a year.

Some astronomers said in April the ball was a confirmed extrasolar planet; others disagree. If it is a planet, it is no place for humans, at five times Jupiter's size and waltzing closely around the brown dwarf, a kind of failed star.

Michel Mayor of Switzerland's Geneva Observatory, a discoverer of the first-known extrasolar planet, said he expected most normal stars to have the potential for planetary systems.

"I think it would be amazing to say that they're not around many stars, but to say that they're around every star would be I think pushing it," Mayor said.

More planet discoveries would mean a larger data base, which would help determine the best conditions for planet formation. Technology is also expected to develop that would allow detection of ever-smaller planets, to the size of Earth.

Already some astronomers have moved from seeking extrasolar planets to exploring those already found. These include Matthews, who works with the Canadian spacecraft known as MOST -- short for Microvariability and Oscillations in Stars.

A tiny orbiting "suitcase in space," MOST watches stars with extrasolar planets to see how they dim as their planets pass. It can also monitor the reflected light from big Jupiter-type planets circling close to their stars.