Question: On the occasion of discovering the first earth-sized planet that could possibly support liquid water, what value would you assign to the Drake equation variable ne (the average number of planets that can potentially support life per star that has planets)? – Richard
Answer: In fact, a recent study using the Kepler telescope estimated that 22% of Sun-like stars contain Earth-sized planets orbiting their stars in their habitable zone. This results in an estimate of about 20 billion Earth-like planets in our galaxy. So, I guess that would mean that ne in the Drake Equation would be 0.22. Note, though, that this is just one study. As additional Kepler measurements are analyzed I expect this estimate to be improved.