Ask Dr. SETI ®
Dear Dr. SETI:
The Doctor Responds:
Of about a dozen extra-solar planets detected so far, only one has been clearly in the habitable zone of its star. So for ne, the number of Earthlike planets per solar system, I'd have to estimate only about 0.1. This does not consider the possibility of habitable moons.
Both of these estimates are highly uncertain, because our sample size is pitifully small. But we expect habitable planets to be rather commonplace throughout the cosmos (that's not a very specific answer, but an encouraging one).
See Solving the Drake Equation for a further perspective on this question.
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this page last updated 28 December 2002
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