• No one really knows for sure, because no one has seen all of them, but for now earth is believed to be the only inhabitable planet.
  • All of them. The only one that may be able to have life is Mars, but you still have to have specially made biodomes to live in.
  • By humans? and with out biodomes? 1.
  • No way to guess or estimate. But think of this: As Carl Sagan said "there are billions of stars and galaxies" so who knows for sure. We could be the only ones or one of billions.
    • mushroom
      "Star Trek" would have been particularly boring if all they did for 5 years was pass by uninhabited planets.
  • I was under the assumption that some were not just for the fact that the gravity on the planets surface would turn us into a pancake, like Jupiter. So I know that not all of the planets are inhabitable, at least not yet.
  • One scientist estimated that in our galaxy alone, at least tens of millions. My majic wand sparked out on you, Jenni. I'll have to wait until next week.
  • I don't know about the universe, but in our solar system: Mars was once inhabitable, Earth is, and scientists are considering Saturn to be the most viable choice as an alternative home planet when we finally wreck this one completely.
  • 4-30-2017 That is not an estimate, it is an out and out guess. There is not even one fact on which to base an estimate.

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