Finding Planets in the Habitable Zone
by Jeff Zweerink
The inevitable finally happened. Astronomers using the Kepler Telescope detected five Earth-sized planets orbiting in the liquid water habitable zone. Yet, unlike previous bold assertions that such planets will host life, a more circumspect attitude surrounded the announcement.
Kepler regularly monitors roughly 150,000 stars for decreases in light that might signal a planet transited across the face of the star. Using observations taken in 2009, the number of planet candidates seen by Kepler grew to 1,235. (Each of these “candidates” needs follow-up for confirmation, but future observations will likely confirm all but a small fraction as actual planets.)
This catalog includes 184 objects Jupiter-sized or larger, 662 Neptune-sized objects, 288 “super-Earths” (roughly 10 times the mass of Earth), and 68 Earth-sized objects. Of all the candidates observed by Kepler, 54 orbit in a region where liquid water could exist. Now it appears that five of those 54 candidates were both Earth-sized and in the liquid water habitable zone!
The first detection of these five planets prompted an editorial in a recent issue of Nature about what constitutes a habitable planet…
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