Sunday, January 13, 2013

"3,000 Exoplanets and Counting"

From Discover Magazine:
... Christopher Burke of the SETI Institute highlighted one of the latest batch of Kepler planets, currently burdened with the catalog name KOI 172.02. Based on the latest analysis, this is a world just slightly larger than Earth (20,000 miles wide, perhaps) circling a very sunlike yellow star every 242 days, at a distance that is just right for liquid water. It is, so far as we can tell, a near-twin of our own planet—certainly the closest that anyone has found so far.

... But that is just a single example. Francois Fressin at the Harvard-Smithsonian Center for Astrophysics has done a clever analysis to find out how many Earth-size worlds are out there in total. After sorting through the Kepler dataset he has good news. “Almost all sunlike stars have planets,” he announced, “and at least one in six stars has an Earth-size planet.” The true fraction is very likely even better than that. John Johnson at Caltech pushed the numbers further and came up with an estimated tally of allthe planets in our galaxy. He made headlines recently when he announced his result: 100 billion planets in our galaxy alone. (There are also 100 billion other galaxies in the universe. Do the math, if you dare.) Again, that’s a lower limit, held back by the fact that Kepler has been operating for less than four years.

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