And Another Thing 2: billions of Earthlike planets
Habitable alien planets similar to Earth may not be that rare in the universe, in fact there may be a whole lot of them, according to recent findings drawn from data obtained by NASA's planet-hunting Kepler spacecraft.
While the researchers had to do some statistical extrapolation to account for limitations of the technology, and they did use a rather generous definition of "Earth-size planet," including up to twice the diameter (and so eight times the volume) of the Earth, the number they came up with is still stunning: About one in five Sun-like stars could have an Earth-size planet in the so-called habitable zone, the range where liquid water - and, potentially, life as we know it - could exist. The nearest such planet could be just 12 light-years away, which on a galactic scale is barely more than down the block: Compared to the distance across the Milky Way, it's the equivalent of a quarter-mile compared to the air travel distance from Boston to Los Angeles.
How many such planets could there be? If the research team's estimates and judgments are correct, there could be 11 billion of them in the Milky Way alone. So even if they were too optimistic by a factor of 10, that would still indicate over a billion potentially habitable planets in the Milky Way.
Of course, a planet being in the habitable zone doesn't mean there is life there or even that life could be supported there: The planet might, for example, have no atmosphere or have one so dense, like for example the one around Venus, that pressures and temperatures at the surface would make life impossible. It doesn't even mean that even if the conditions for life exist there, that life actually got started. It just means that life as we know it is possible there.
So we still don't know if there is life out there - but with it being within the bounds of reason to say there the galaxy has well over a billion shots at it, well, the chances for it just keep getting better.