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| Life in the Universe |
1. We cannot make statistical arguments from a single case. The single case shows that it is possible for life to evolve around a G2 star, but it cannot show that this is the most likely place. It could be, for example, that it is millions of times more likely to find life around a K star than a G star; we have no idea at this point, because we have only one data point.
3. Two obvious things occur immediately. First, the tidal heating of the inner Galilean moons of Jupiter makes their interiors much warmer than we would normally expect. Thus, it is possible that Europa has a subsurface liquid water ocean, even though on its surface it is far too cold for water to be liquid. Second, greenhouse effects can raise the temperature of an atmosphere far above that expected given the distance of the planet from the Sun. These types of effects (and probably some others) could make the temperature of a planet well out of the habitable zone conducive to life in particular instances.
5. The nearest star lies in the alpha Centauri system, about 4.3 ly away. Therefore, at 10 percent of light velocity it would take 43 years to reach it.