NASA's search for another Earth narrows: Meet our closest twin yet

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.

Scientists have now zeroed in on the most Earth-like of Earth-like exoplanets to date. KOI 172.02 (Kepler Object of Interest — yeah, it's a mouthful) is just a tiny bit larger than our own "Blue Marble," with a diameter 1.5 times our planet's. Its orbit is really close to Earth's own calendar year, as it takes just 242 days to circle its star. Space.com has a neat infographic comparing the two.

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KOI 172.02 leapfrogs to the front of the pack of potential Earth twinsies, which includes one-time frontrunner Gliese 581g (20 light-years away) and Gliese 667Cc (which lives in a triple-star solar system).