How many planets might be suitable for human-like life.
Wikipedia is a great place to start.
1 Suitable star systems
2 Planetary characteristics
3 Alternative star systems
4 Four classes of habitable planets based on water
5 The galactic neighborhood
6 Other considerations
Since no other planet has ever been found that supports high level life forms, it is somewhat anybodys guess what might work.
The SETI (search for extra terresteral intelligence) program has been listening for radio signals with coherent signals for decades without finding anything. Which also does not prove very much.
However, with no signs of higher forms of life my inclination is that planets like the Earth are rare, or that life only lasts for a relatively short time (we could be heading there) making it less likely that we would detect a radio signal.
The main outcome is to make the earth more precious and is an incentive (as if we needed one) to preserve it.(emphasis is mine)
On 4 November 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs within the Milky Way. 11 billion of these estimated planets may be orbiting Sun-like stars. The nearest such planet may be 12 light-years away, according to the scientists.
What to make of this is extremely difficult. Noble Prize winning astro-physicists are certain there are other planets inhabited with higher life forms, and if we put our egos aside, among 40 billion earth size planets there must be many inhabited with higher life-forms.
Quoting from Wikipeia again:
"11 billion of these estimated planets may be orbiting sun-like stars. The nearest such planet may be as close as 12 light-years away. On August 24, 2016, astronomers announced the discovery of a rocky planet in the habitable zone of Proxima Centauri, the closest star to Earth." 12 light-years, or 7 x 1013 miles is well beyond our technology.
Next is to assess just how overheated the Earth is and what that is causing today. After that we will take a longer look.