Planets Common as Stars in Galaxy: Analysis Suggests Milky Way Contains 100 Billion Planets

Article excerpt

When you turn an eye to the evening sky, there's a good chance that many of the stars you see have at least one planet.

Using six years of data from planet-finding surveys, an international team of researchers concludes that, on average, a star in the Milky Way is accompanied by 1.6 planets. That's at least 100 billion planets in all, the scientists report January 12 in Nature.

The figure might seem enormous, but it doesn't shock planet hunters. "I'm not surprised by this result," says astrophysicist Wesley Traub of NASA's Jet Propulsion Laboratory in Pasadena, Calif., who was not involved in the study. "This sounds reasonable. This sounds good."

The scientists used data that had been gathered from 2002 to 2007 by surveys looking for temporary brightening in a distant star's light caused by the gravity of a body passing in front of it. If that passing body is a star with one or more planets, the system causes a predictable boost in the distant star's light.

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Unlike other types of planet searches, this technique, called gravitational microlensing, works well for stars both near Earth and far away. "If we want to go out of our little box and see into the infinite universe, or in the galactic bulge, or far outside the galaxy--are there planets even there? …