What's the Latest Development?

NASA's Kepler spacecraft has discovered two planets roughly the size of Earth orbiting foreign stars. The planets, Kepler 20f and Kepler 20e, orbit a sun-like star about 950 light years away and are the smallest exoplanets for which diameters are known. "For the first time, we've crossed the threshold of finding Earth-size worlds," said Guillermo Torres of the Harvard–Smithsonian Center for Astrophysics. "The next step is having an Earth-size planet in the habitable zone." 

What's the Big Idea?

The new scientific techniques that have allowed the recent discovery of so many exoplanets—506 and counting—have yet to be perfected. We do not know the composition of Kepler 20f and Kepler 20e because scientists cannot yet measure their mass. But given the proximity of the planets to their star, surface temperatures are likely too hot to support life, at least as we know it. Still, it now seems only a matter of time until a foreign rock is found that is capable of sustaining life.

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