Oh yea I just realized it obviously has to be quite low, shouldn't be too hard to estimate for earth (the problem is, it varies with planet size). I would guess

Oh yea I just realized it obviously has to be quite low, shouldn't be too hard to estimate for earth (the problem is, it varies with planet size). I would guess two orders of magnitude or more actually, which would indeed put the expected number close to 1. A naive calculation for Earth would be Theta ~= 2 * (Earth diameter) / (Mean distance to Sun), which is ~2*10^-4. Since most planets found by kepler were much larger than earth, it seems 10^-2 is a reasonable guesstimate.