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Study: Billions of Alien Planets Fill Our Galaxy

By Space.com

Credit: PHL @ UPR Arecibo, ESA/Hubble, NASA

Planets are being added to the Habitable Exoplanets Catalog regularly. So far none of them is small enough to be considered "Earth's twin," but that's likely to change.

January 3, 2013 Updated Jan 3, 2013 at 9:31 AM PDT

Our Milky Way galaxy is home to at least 100 billion alien planets, and possibly many more, a new study suggests.

"It's a staggering number, if you think about it," lead author Jonathan Swift, of Caltech in Pasadena, said in a statement. "Basically there's one of these planets per star."

Swift and his colleagues arrived at their estimate after studying a five-planet system called Kepler-32, which lies about 915 light-years from Earth. The five worlds were detected by NASA's Kepler Space Telescope, which flags the tiny brightness dips caused when exoplanets cross their star's face from the instrument's perspective.

The Kepler-32 planets orbit an M dwarf, a type of star that is smaller and cooler than our sun. M dwarfs are the most common star in the Milky Way, accouting for about 75 percent of the galaxy's 100 billion or so stars, researchers said.

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