A Baffling Case

Mystery of the Aliens (1)

AS the decades go by, with ever more intensive searches for intelligent alien life, our failure to find it becomes ever more baffling. Science tells us there ought to be signs of aliens everywhere. But no one has paid us a visit or beamed us a message. In Enrico Fermi's famous words: ``Where is everyone?'' All we observe is ``the Great Silence.'' There appears to be nothing out there but natural phenomena. The mystery might perplex the finest detective minds. Imagine it being discussed at 221B Baker Street. ``My dear Holmes, the Sun is an average kind of star. There must be billions of Sun-like stars in the Galaxy. There must be many millions of such stars that have Earth-like planets with `Goldilocks orbits', where it is neither too hot nor too cold.

Holmes, it is brilliant!

And the Sun is a second generation star, only half the age of the Galaxy. So it should contain tens of thousands of older and wiser civilisations than ours. But where are they?'' Sherlock Holmes lit one of his foulest pipes.``If they are not there, Watson, then something is evidently missing from your argument.'' ``But surely I have covered every salient point.'' ``I think not, Watson,'' said my friend severely, ``as usual you see but you do not observe. You point out, correctly, that the Sun is an average kind of star. But has it not occurred to you that we might not be living in the average kind of planetary system?'' ``You mean that other planetary systems are in some way less suitable for evolution?'' ``Well, let us see.'' Holmes took a sheet of paper and drew a rough diagram with the Sun at its centre, surrounded by the orbits of Earth, Mars and Jupiter. He then sketched in a large number of dots between the latter two to indicate the Asteroid Belt. ``Where, one assumes,'' I said, ``that asteroids are randomly distributed.'' ``Assumes! Watson, it is a capital mistake to speculate without data. Does the name of Daniel Kirkwood mean anything to you?'' ``An astronomer evidently.'' ``And a very underrated one. Look again at my diagram.'' I did so and saw huge swathes of emptiness in that part of the Belt that was nearest Jupiter. ``Behold Kirkwood's Gaps, Watson, where, in 1866, he could not find a single asteroid!'' ``Then where have they gone to?'' ``Swept inwards, Watson,'' said Holmes grimly. ``Pushed out of their orbits into chaos by the gravity of fast-moving Jupiter. And every thirty million years or so, one of them strikes the Earth. The fossil record proves it.'' I gasped in horror.``But such events must have been catastrophic for the emergence of life.'' ``On the contrary,'' he said with a chuckle, ``a species rising towards intelligence may need such catastrophes as a detective needs challenging cases. They can drive it into new and advantageous ecological niches. Perhaps other planetary systems lack such precise arrangements and species evolve too slowly. Hence the Great Silence.'' ``Holmes, it is brilliant!'' ``Spare my blushes, Watson,'' he said morosely, for he hated giving credit to others.``The idea comes from Professor John Cramer, of the University of Washington in Seattle. I quote it for what it is worth.''