2 ms·

That's what I thought - "average number of Earth‐like planets per star with planets: 2"... really?

• deutronium 16y ago
  I'd like to know where that value comes from, is there any scientific basis to it?
  • PixelRobot 16y ago
    It seems to be just speculation. There's not much data you can use to guess those numbers with the current scientific knowledge.
  • rflrob 16y ago
    When the equation was first proposed, I'd guess they assumed Sol is an "average" solar system, and given that we have Earth, which is by definition Earth-like, and Mars, Venus, and several of the Jovian moons, which could all fit a suitably loose definition of "earth-like", Drake might even have thought he was being conservative.