Infrared observations of circumstellar disks indicate that ~80% of stars are born with enough material (gas, dust, and water) to produce at least several low planets. High precision radial velocity searches for extrasolar planets tell us that ~10% of solar type stars have at least one planet down to Saturn-mass orbiting in 2000 days or less. Extrapolations and long term trends in these surveys indicate that another 5-10% of these stars may have planets down to Saturn mass out to 20 A.U. The data on smaller planets has remained sparse until very recently--that is, until the Kepler mission started finding smaller planets in high numbers. Specifically, Kepler (with more observation time remaining and a possible extended mission) has told that 34% of stars have at least one planet within 0.5 A.U. By the time this incredible mission is finished, it will tell us that X% of stars have at least one planet within 1-2 A.U. However, it is unclear how many more planets will turn up in future generations of searches. What will the X in X% be?
My question to viewers is this: In light of all of the data existing thus far on extrasolar planets, what fraction of stars do you think will turn out to have at least one planet?