Hi Guys

Interesting article at the ArXive...

http://au.arxiv.org/abs/astro-ph/0204001

...which suggests that systems like ours [the major planets don't migrate too far as the planets form] might be fairly rare - about ~ 1% of Sun-like stars. And that's only ~ 15% of the whole or less. So stable solar systems like ours might be less than 0.15% of the total.

Factoring in all the other complications, planets like Earth might exist around ~ 1 in every 60,000 stars. That makes them about 50 parsecs (163 ly) apart in our part of the Galaxy. And that's an optimistic analysis. Rarer Earths are, the further away they will be.

50 parsecs is already a LONG way to travel...

Adam

suitable systems ~ 0.01
suitable stars ~ 0.15
correct age ~ 0.3
large moon/good axial tilt ~ 0.08
in ecosphere ~ 0.5

In Galaxy (3.0 E+11 stars) ~ 5 million - 0.5 million "earths"