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Could the new Earth-like planets harbor life?

Scientists have discovered a pair of Earth-sized planets orbiting a distant star. Could these planets, dubbed Kepler 20e and Kepler 20f, support life?

By Natalie WolchoverLife's Little Mysteries / December 21, 2011

An artist's rendering shows a planet called Kepler-20e. NASA's Kepler mission has discovered the first Earth-size planets orbiting a sun-like star outside our solar system, a milestone in the search for planets like the earth, the space agency said on Tuesday.



For life as we know it to arise on another planet, scientists think the alien world must have three key ingredients: organic molecules that can form complex structures, energy to jiggle those molecules, and liquid water for them to jiggle in. It's a short recipe, but nonetheless, only planets that are extremely similar to Earth can possibly have all three items in stock.

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If a planet is much closer to its star than we are to ours (and assuming that star is similar in size to our sun), all the water on its surface will evaporate in the heat. If it's much farther away, all its water will freeze. Similarly, planets much larger than Earth are gaseous, with no solid surface for an ocean to slosh around on, while those much smaller wouldn't have had enough gravity to form in the first place. Thus, in the search for "candidate planets" which could host alien life, "alien Earths" are the Holy Grail.

In a paper published today (Dec. 20) in the journal Nature, a team of scientists who study data collected by NASA's Kepler telescope report the discovery of a pair of exoplanets, or planets outside our solar system, that are almost exactly the same size as Earth. The distant worlds, labeled Kepler-20e and 20f, orbit a star called Kepler-20 located 950 light-years away, and have diameters 0.87 times and 1.03 times that of Earth, respectively.

At those sizes, the planets' gravity would be strong enough to make them rocky like Earth, rather than gaseous like Jupiter. "Theoretical models suggest that the material inside the planet could be iron in the core surrounded by a mantle of silicates," said Guillermo Torres, a member of the Kepler team based at the Harvard-Smithsonian Center for Astrophysics. If that's the case, they would have, respectively, masses 1.7 times and three times Earth's mass, he said. [Infographic: Earth-Size Alien Worlds]

The planets are roughly Earth-size, but do they have what it takes to sustain life? Unfortunately, not quite. "These are just way too hot to be habitable," Torres told Life's Little Mysteries.

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