
Originally Posted by
kzb
One thing to watch out for is the definition of "habitable".
In this context it means liquid water could exist on the planet surface, given atmospheric pressure in the correct range.
it does not mean that you could go and live there necessarily.
Having got that out the way, 100 billion seems quite reasonable. There is a paper out there which estimated the average sun-like star has more than one habitable planet.
This is not unreasonable when you think about it. Venus could've been just a bit further out, or Mars could've been a big bigger, and we could have three habitable planets right here in the solar system.
Then there is the fact that most stars are red dwarfs, and at the present they are assuming there is nothing stopping red dwarf planets being habitable, by the above definition.