Article by Frank Morring, Jr., Aviation Week and Space Technology.

Excerpt: Last time, NASA’s Kepler planet-finding mission found a planet in the right orbital location to support life, but it was the wrong size. This time, Kepler has found two planets of the right size but in the wrong location.

The Kepler team reported Dec. 20 that it has located an Earth-like star called Kepler-20 orbited by five planets, including two — Kepler-20E and -20F — that are the closest in size to Earth of any planets yet discovered outside our own Solar System. But they are so close to their own star that they are too hot to support life.

The other three are giant gas planets like Jupiter that lack the requisite hard surfaces or atmosphere likely to support life.

...Unlike planets in our own Solar System, which can be neatly separated by an “ice line” between the smaller, rocky planets that orbit closest to the Sun and larger gaseous planets farther out where surface temperatures are much colder, the Kepler-20 system mixes the two types up.

“The architecture of the [Kepler 20] system is crazy,” Charbonneau says. First there is a Neptune-like gas bag, followed by -20E, then another Neptune, followed by -20F and finally another Neptune. “It’s big, little, big, little, big ... that we know of,” he says. “All five orbit within a distance of Mercury to the Sun.” Mercury is closest to the Sun.

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