Seventeen billion. That's how many Earth-sized planets exist in our Milky Way galaxy, according to new estimates from NASA. That's enough for every man, woman, and child alive to have at least two planets to call his or her own.
The revelation is why scientists who are part of NASA's Kepler mission — charged with scouting new alien worlds — are suddenly so enthusiastic about the odds of finding Earth's twin. At the meeting of the American Astronomical Society earlier this week, the Kepler team named 461 new candidates to add to its ongoing tally of 2,740 potential "New Earths" inside what's called the Habitable Zone, a just-right distance from a planet's respective star. In theory, planets within this "Goldilocks zone" could have similar surface temperatures and climate conditions conducive to liquid water, and perhaps — a big perhaps — even support life.
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