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  • Print publication year: 2014
  • Online publication date: February 2014

2 - The Once and Future Sun


It would be overly optimistic of us to think that we have any accurate understanding of the conditions that make life possible. We do know that life exists on Earth, that it does not seem to have ever existed on the Moon, and that it may or may not have existed on Mars and Venus. If there is life elsewhere, such as on a moon of Jupiter, we have not yet found it. This means that we have exactly one data point, and it is dangerous to generalize from a single example. After all, in recent years we have seen many types of solar systems containing the thousands of exoplanets that have been discovered, and realized that most of them are very different in format from our own solar system. Generalizing from our own solar system turned out to be very wrong.

Still, as far as we can tell, light and heat have been of central importance. The Earth would not have life on it if the Sun had not brought the surface temperature of our planet above the freezing point of water, but well below the boiling point. We are not in a good position to argue that this range of temperatures is absolutely essential for life, but it is generally necessary for the types of life that we see here.

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