Here is a great video about the newly announced Kepler 452b with SETI scientists: Douglas Caldwell, Jeffrey Coughlin, Joseph Twicken. and hosted by Seth Shostak.
The Hangout fills in a lot of the blanks from the news reports. As I expected we don’t yet have a mass or density on this planet. Once we get at least a good estimate on these numbers for 452b then we will be able to make better guesses on its composition.
We have an estimate of the diameter so that’s a start, but it’s only one bit of the equation that defines the balance the must exist. If for example, 452b has the density of Earth, we might expect an atmosphere to be much different than we have, ranging up to perhaps even Neptune-like. On the other hand the mass could be much less and the weaker gravity could allow more of the lighter gasses to be lost to space.
I am bound to guess we are very close to finding a real Earth analog. It is astounding how quickly the search is progressing.