Life, Unbounded: An Abundance of Exoplanets Changes our Universe

...Even with sizable errors in these estimates (as much as 20-30%) the numbers are astonishing – there are at least 1.6 planets orbiting from 0.5 to 10 AU for every star in the galaxy. Combine this with the Doppler survey numbers (25% of stars with ‘Earth-sized’ planets within 0.25 AU), the Kepler numbers (17% of stars with ‘Neptunes’ orbiting within 0.5AU), and the microlensing estimates of 2 rogue giant planets per star in the galaxy and you have, well you have an awful lot of planets. ...

...Thus, the sheer abundance of planets profoundly impacts the nature of our exploration of the universe and our quest to understand our own significance or insignificance. There is nothing trivial about the discovery of planetary plentitude, because it means that we are finally on the cusp of seeing whether a statement made two and a half thousand years ago is correct or not:

“To consider the Earth as the only populated world in infinite space is as absurd as to assert that in an entire field of millet, only one grain will grow”

- Metrodorus of Chios (Fourth Century B.C.)

It’s extraordinary to think how far we have come since these words were written.

(Oh, and as for moons, well don’t even begin to go there. Our solar system carries over 160 natural satellites around with it, so moons might yet turn out to be the most numerous planetary-type bodies of all…) [1]