Wednesday, November 07, 2007

Welcome to the club

They haven't discovered an Earth-like planet yet, but astronomers are getting closer every year. 55 Cancri A, the larger member of a nearby binary star in Cancer (41 light-years away), now has a confirmed five planets, including a large outer giant, as well as four inner medium-sized giants. The system might have Earth-like (rocky) planets with thin atmospheres, but those still lie below the threshold of detectability. It's also possible that these planets have Earth-like moons (bigger versions of Saturn's Titan) with atmospheres. OTOH, keep warm oceans in mind too, if you're looking for life.

The parent star is 0.61 as luminous as our Sun. Thus the distance for Earth-equivalent light flux from 55 Cancri A is (0.61)1/2 AU = 0.78 AU, roughly the Sun-Venus distance (0.72 AU). (One astronomical unit, or AU, is the Sun-Earth distance, 93 million miles = 150 million km.) One of the 55 Cancri A planets is about that close to the star, so a rocky moon is a contender for Earth-like conditions.

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