美国科学60秒 SSS 2013-01-08

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　　“There are in fact 100 billion galaxies¹, each of which contains something like a 100 billion stars.” Well, Carl Sagan would have loved to get the latest estimate of our galaxy²’s planet count.

　　Caltech astronomers³ set their sites on a star called Kepler 32. It’s an M dwarf⁴ star, a class that’s smaller and cooler than our sun, and accounts for about three quarters of the stars in the Milky⁵ Way. But what’s really cool about this particular star, from the astronomers’ point of view, is that its five planets orbit in a plane that the Kepler telescope sees edge on. So the star’s light dims each time a planet passes between it and the scope, which makes the planets easier to detect.

　　Now, taking into account the percentage of M dwarf systems that lie in a similar edge on orientation⁶, and the number of planetary systems the Kepler telescope has already detected, the researchers figure our galaxy is host to at least 100 billion planets. Their calculations are served up in The Astrophysical Journal.

　　Many of those planets may be the size of Earth. But we’re the only planet that produced Carl Sagan.

　　Thanks for the minute for 60 second science,  I am Karen Hopkin(天文领域的文章，不好懂)

　　galaxy: 银河

　　edge on: 侧向

　　M dwarf: 红矮星

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