Are humans the real ancient aliens?
by Seth Shostak
Harvard Astronomer Avi Loeb and his colleagues in the U.K. have argued that the halcyon days for life are still to come. It's not even morning in the universe; it's pre-dawn. Biology may erupt like weeds on an untold number of worlds, but if so, the infestation will take place tens of billions of years in the future.
The argument is straightforward: The longer you wait, the more examples of biology you'll have. But stars like our Sun can't wait too long: there's a relatively short opportunity to strut and fret. In 10 billion years, they've run through their easily accessible fuel, and are headed out the door.
But consider red dwarf stars, the runts of the universe. Their masses are considerably less than Sol's, which means they burn more slowly. The consequence? Red dwarfs with one-tenth the mass of the Sun have lifespans that are up to a thousand times longer.
All else being equal, that would give red dwarfs a thousand times the probability of eventually using its energy to host a world with life. Clearly, it's most probable that this life would arise not when these stars are still young — which they all are now — but instead during their long adulthood. In other words, the red dwarfs are just getting started, and their biologically fecund years are still ahead.
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