[g__day (Matthew)]

I've read about the number of factors (about 31 key ones) that have to align for a plamet to support life - this was the the Ne factor in this famous equation. I think the best estimate for any planet in the Universe to have conditions suitable to support life are extremely low - roughly less than one in google chance for any life - let alone advanced life. You really have to fluke many factors that include:

1. Age of Sun
2. Size and mass of Sun
3. Distance of Sun from galactic core (about 2/3's out is optimal)
4. Size of planet
5. Mass of planet (no more or less than 10% Earth's weight)
6. Distance of planet from Sun (You need the right temperatures to support life)
7. Presence of Moon
8. Size of Moon and distance from planet
9. Planet requires and Iron core (you need a magnetic shield to eliminate radition that would otherwise sterilise all life)
10. Planet requires abundant water in liquid form (to mix chemicals, act as a heat buffer and resevior etc)
11. Planet requires plate tectonics
12. Planet requires silica balance
13. Planet requires one or more gas giants further out in solar system (to vaccuum up killer asteroids during solar system creation and the next few billion years)
14. Presence of Ozone (need to deflect ultra violet radiation)

And so on for another twenty factors - any one of which being set wrong means the raw building blocks of life aren't likely to form or be preserved.

Basically you're cross multiplying 31 factors that might have a one in a hundred to one in a billion. Say on average a one in then thousand chance - then that is 10 ^ 31 * 4 or 10 ^ 120.

We guesstimate there is around 10 ^ 26 planets in our Hubble sphere.