Well, in the great tradition of Blazing Saddles, we should call all planets discovered that are like ours "Earth" but with a different prefix like Olsen Earth, Samuel Earth and Howard Earth
Now that is one wildy optimistic article about habitability. The old Sky and Space magazine covered the skeptic's case pretty well. From memory:-
90% of stars are red stars - where the habitable zone winds up having it's "earth" tidally locked to its star - hot on one side, the other side cold. In other words, nothing like earth at all.
There's only a small band around the galaxy where earth-like planets are possible - further in from that band and the rocky planets are expected to be much larger, further out and they are expected to be much smaller. From memory, this ruled out about 95% of stars.
Then there's the issue of an earth-like planet going around multiple star systems, which are around 40% of stars, and their effects on its orbit.
These rule out over 97% of stars, this still leaves tens of millions of possible stars with earth sized planets.
But the big doozy, is how many of the remainder of those planets are going to have a stable axis of rotation from having a huge moon created by a huge asteroid impact in it's past?
Regards,
Renato
