Astronomer hopes to spot an inviting planet or two



Marc Kuchner at Goddard Space Flight Center is aiming to attack a question that has puzzled us since we first peered into the heavens: Are we alone in the universe?

Kuchner came to the Greenbelt research center six months ago from Princeton to step up a search for habitable Earth-like planets outside our solar system.

He is writing a proposal for NASA funding for a new space hunting probe and, over the next few years, plans to hire a staff of five or six researchers for the fledgling ExoPlanets and Stellar Astrophysics Laboratory. The size of the staff will depend on future NASA funding, he said.

The research is aimed at determining not only whether Earth-like planets exist elsewhere, but how they formed and whether any of them could make a future home.

"One goal is finding some planet we can visit when we use this one up," he said.

The search for extrasolar planets is a relatively new field for astronomers. The first ones weren't discovered until the 1990s. Since then, more than 150 have been detected, but none are anything like Earth. Almost all of them are gas giants like Jupiter, but orbiting so close to their stars that their surfaces are as hot as skillets.

"They're extremely hot. That's why they're called `hot Jupiters,'" said William J. Borucki, a scientist at the NASA Ames Research Center in California.

A few hot Jupiters have been detected by measuring changes in light as the planet passes in front of its star. Others have been found by gravitational lensing, in which light from a star is magnified by light from another star passing nearby.

But most of the extrasolar planets found so far have been detected by measuring the radial velocity, or "wobbling," of light from the star being orbited by the planet. The wobbling is produced by the gravitational pull of the planet as it orbits the star.

"We don't see the planets directly. We infer the presence of the planet by its effects on the star," said Alan P. Boss, a planet hunter at the Carnegie Institution in Washington.

Wobbling is easier to detect in stars being orbited by Jupiter-sized planets because they make the stars wobble more, Boss said.

But ground-based telescopes have been unable to detect any habitable Earth-sized extrasolar planets because light from them is obscured by the stars that they orbit, experts say.

"If we could find them from Earth without spending $500 million by putting a satellite in space, we would," Borucki said.

Borucki is principal investigator of the Kepler Mission, a satellite scheduled for launch in 2008 that will spend four years looking for new planets by staring at 100,000 stars and waiting for planets to cross their paths. Kepler will focus on the constellation Cygnus because it holds the greatest known concentration of stars, Borucki said.

"We're basically building a giant camcorder, putting it in space and seeing if the stars that it captures dim every so often," he said.

Kuchner's proposal, called New Worlds Discoverer, would be launched with the James Webb Space Telescope in 2013 and would block out star light obscuring orbiting planets.

The satellite would orbit between the Webb and stars suspected of being at the center of a planet's orbit. It would use a star-shaped mask to block out light from stars one at a time - the way you might put your hand out to block a light that is shining in your eyes. Blocking out the light will enable the Webb to gather light from planets that were previously obscured by their stars.

"This is going to find us some Earths," Kuchner said. He is working on the project with Webster Cash, a planetary scientist at the University of Colorado.

Kuchner says that the $400 million project would be an appropriate follow-up to Kepler because it will detect planets that are closer to home. New Worlds will find planets about 30 light years away, while Kepler is searching in regions thousands of light years away.

"Ours will be planets that we could actually dream of visiting someday," Kuchner said.

He is convinced that a wide range of exotic planets, made of different materials than the silicon and oxygen that make up most of Earth, are waiting to be discovered. Planets made entirely of carbon, of water or of compounds we can't imagine are possibilities, he said. A planet's composition depends on what kind of material was available when the planet formed.

"It all depends on the exact chemistry of the proto-planetary dust," he said. "It's just a matter of shuffling the dust around to make for conditions that would be really different."

The New Worlds satellite also may help resolve mysteries about how planets form and why the Jupiter-sized extrasolar planets found thus far are orbiting so closely to their stars.

Accepted theories about planet formation say that large planets, like Jupiter, should evolve much farther out from their stars. Some experts think the hot Jupiters formed far out from their stars and then migrated inward. But no one is sure.

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