Mr. Marcy, shown here in Berkeley, regularly conducts his research --
which is the discovery and cataloging of planets --
 from the W.M. Keck Observatory on Mauna Kea in Hawaii

New Information from NASA Could Offer Evidence of a Habitable World Beyond Our Solar System


Astronomers seeking new worlds capable of supporting life will next week unveil data on hundreds of possible planets circling other stars, quickening the pace of the high-stakes quest for the first habitable world outside our own solar system.

The flurry of new information on so-called exoplanets—those that orbit stars other than the sun—includes 400 promising prospects that NASA researchers have kept to themselves since their discovery last spring.

A carbon copy of Earth, warm and wet enough for the chemistry of life, is unlikely to be revealed among them—at least not yet. The new data, though, may offer important evidence of planets that are at least Earth-size and more likely to harbor life as we know it.

The information is the product of a survey of 156,000 stars conducted by the space agency's $600 million planet-hunting Kepler space probe, which was launched in 2009.

Since June last year, when NASA released some preliminary probe data, the Kepler mission scientists have been cross-checking data on 706 stars that may have planets orbiting them, ranging from as small as Earth to larger than Jupiter, and weeding out false alarms with the help of ground-based observatories. More possible planets have subsequently turned up, as the probe continues to send more data back to Earth.

"We have found more interesting planet candidates," said Natalie Batalha, deputy science team leader for the Kepler Mission at NASA's Ames Research Center in Mountain View, Calif.

The probe can detect a possible planet by measuring its shadow as the orb crosses in front of a star and by recording the tiny variations in starlight as it dims and brightens. Astronomers working at independent observatories then double-check the candidates by looking for gravitational wobbles caused by the planet tugging on the star it circles.

The Kepler researchers have been keeping the most intriguing data under wraps, but the scientists are now racing to finish research papers for publication in advance of a flurry of formal announcements next week.

"The history of exoplanets is littered with people racing to be the first," said planetary physicist Sara Seager at the Massachusetts Institute of Technology.

Astrophysics professor Sara Seager posed for a
 portrait at the Massachusetts Institute of
 Technology in Cambridge, Mass.
She and her students are working on a satellite
 telescope that is a prototype of a
 next generation mini-probe to hunt for
 Earth-like planets.

During the past 15 years, researchers in the U.S. and Europe have discovered 519 planets orbiting other stars, but none of them resembles Earth or appears suitable for life. So far, they're too hot, too cold, too big or simply too weird.

The search has yielded a catalog of unearthly wonders. Circling other stars are planets hot enough to melt iron and rain lava. There is a Jupiter-size giant with the density of Styrofoam and a world of carbon that might have a core of diamond. One exoplanet orbits its star backward; others confound traditional theories of planet formation and the evolution of solar systems.

It also has triggered false alarms and technical disputes.

Undergraduate seniors Dora Aldama, left,
and Mary Knapp assembled a model
satellite telescope in a lab at MIT.

Last September, researchers led by astronomer Steve Voigt at the University of California at Santa Cruz announced the discovery of what they said was the first known habitable planet, which they named Gliese 581g. They used 11 years of data from observatory sensors to pinpoint it among four or more other planets orbiting the same star.

But astronomers at the Geneva Observatory in Switzerland, who studied the same star system, quickly announced they couldn't find any sign of it. Last week, Philip Gregory, an expert in astrostatistics at the University of British Columbia, reported that it was most likely the product of instrument error.
"When I looked at the false-alarm probability, it is very high—sufficiently high that one would never dream of claiming detection of this planet," Dr. Gregory said.

Nonetheless, Dr. Voigt said he stood by the discovery, which was peer-reviewed at the Astrophysical Journal. In his view, the critiques are seriously flawed. "Whether or not these planets are real will only be answered by more data and that will probably take a few more years," he said.

In the meantime, nobody can say with certainty whether any habitable planets exist outside our solar system.

"They might be one in a million in the Milky Way or they might be a dime a dozen," said planet-hunting pioneer Geoffrey Marcy, a professor of astronomy at the University of California in Berkeley who also works at the W.M. Keck Observatory on Mauna Kea in Hawaii.

To arrive at a working estimate, Dr. Marcy and his colleague Andrew Howard spent five years surveying the frequency of planets among 166 of the nearest and brightest sun-like stars. They calculated last October that there ought to be about 23 Earth-size planets for every 100 sun-like stars, meaning there could be billions of such worlds in the galaxy.

If so, the Kepler probe, which has 43,000 sun-like stars in its field of view, has already collected a lot of data about them.

In a rare disclosure earlier this month, the NASA scientists announced the discovery of their first Earth-size exoplanet. Called Kepler 10-b, it's a rocky world about 1.4 times the size of Earth with the density of a dumbbell but much too hot for life. The star it orbits, a thousand times fainter than can be seen with the unaided eye from Earth, was among the first identified by the space probe.

"It popped right out," said Dr. Batalha. "We know unquestionably that this is a rocky planet."

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