And 500 million is just the estimated number of possibly life-bearing exoplanets for our very own Milky Way Galaxy.
From the "Atlas of the Universe" we find these estimates cited for galaxy numbers in the rest of the Universe:
|Number of galaxy groups in the visible universe = 25 billion|
|Number of large galaxies in the visible universe = 350 billion|
|Number of dwarf galaxies in the visible universe = 7 trillion|
|Number of stars in the visible universe = 30 billion trillion (3x10²²)|
So, how very high are the chances of life of various sorts existing elsewhere, or of having existed elsewhere, in the Universe?
The estimate of 50 billion planets in our galaxy seems to be a bit low considering that there is an estimated 200 billion+ stars in the galaxy without knowing how many red dwarfs there are - which could have habitable planets. But 500 million is a pretty promising number for possible habitable planets. I would speculate that the chance of life on at least a few is close to 100%.
Good point, yeah.
Well, except you'd think that larger suns would have a larger Goldilocks zone, further out from the primary ... unless there's something different about the radiation of those stars that makes them bad, even in the Goldilocks zone ...
The hard line for life "as we know it" to exist is the range between 0 and 100 degrees centigrade. Our biological system requires liquid water. Actually though, the higher end of the range is a bit tighter than that. DNA uncoils and stops functioning properly, well below the boiling point of water.
I saw the exact number in an article discussing how DNA testing works, explaining how DNA unzips at a certain temperature, if it's a perfectly matched set, but unzips at a lower temperature, the more unmatched genes there are on either side of the helix. This is how we figure out what percentage of genes two different species share. I think it was linked off of some post on Atheist Nexus, but I can't remember where it was from.
"as we know it"
All life in the universe might not be as we know it.