- The Washington Times - Wednesday, February 2, 2011

At least five Earth-sized planets appear to be orbiting their stars at just the right distance to host liquid water, NASA said Wednesday, announcing a significant step in the agency’s search for extraterrestrial life.

The Kepler telescope gleaned an extraordinary amount of new information in less than two years of Earth orbit, observing a small slice of the Milky Way galaxy.

The discoveries include whole solar systems and planets close enough to each other to give scientists clues about what they are made of — thus how hospitable to life they may be.

“Not only is Kepler telling us about planetary systems of a type that we had no idea existed, but right now it’s providing our best clues on the composition of these planets as individual worlds,” Kepler scientist Jack Lissauer said Wednesday at a briefing to announce the discoveries.

Several hundred new “planet candidates” — they are, for now, just known to be celestial bodies — bring the Kepler mission discoveries to 1,235 possible planets, potentially tripling the count of extra-solar planets from the current 519.

Of those bodies, 68 are about the size of Earth, and five of those Earth-sized bodies were observed in what scientists call the “habitable zone,” where liquid water could exist on a planet’s surface.

“If we find that Earth-sized planets are common in habitable zones of stars, it’s very likely that life is common around these stars,” Kepler scientist William Borucki said Wednesday.

Before Wednesday, there were only thought to be at most two extra-solar planets in their system’s habitable zone.

Another 49 planet candidates were found by Kepler in the habitable zone, but their enormous sizes suggest big, gassy planets more like Saturn, which, regardless of their distance from their star, cannot sustain life.

The Kepler mission has also turned up 170 stars that appear to be orbited by multiple planets. Such systems are crucial because the planets’ effects on one another’s orbits allow scientists to glean more information about their environments.

“We’re studying systems of planets,” Mr. Borucki said, describing multiplanet systems as “the most valuable things that we can find.”

The largest such system so far has six planets orbiting a star dubbed Kepler-11.

“The five inner planets are essentially close together, something that we didn’t think would happen for worlds of this size,” Mr. Lissauer said. The planets’ proximity means they are disturbing one another’s orbits enough to determine what they might be made of, he said.

The inner two possible planets of this system could be mixtures of rock and water or rock and gas, while the outer planets are large for their mass and must be made of large parts hydrogen and helium, Mr. Lissauer said.

Such a pattern would be similar to our solar system, which has four small, rocky “inner planets” (Mercury, Venus, Earth and Mars) and four large, gassy “outer planets” (Jupiter, Saturn, Uranus and Neptune).

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