Life CAN Appear - But WILL it?  

Mars has always been of special interest to us; it is less unlike the Earth than any other planet in the Solar System, and it has long been regarded as a possible abode of life.  True, Percival Lowell’s canal-building Martians have long since been banished to the realm of myth, but we cannot yet be sure that Mars is, and always has been, completely sterile.  Certainly there must once have been liquid water there, so that in the remote past Mars was much less unwelcoming than it is today; we may be seeing the Red Planet at its very worst.

The Viking missions of the 1970s showed no definite signs of life, though it must be admitted that the results were not clear-cut; there is something decidedly peculiar about Martian chemistry.  In 1997 we have had Pathfinder and Global Surveyor; neither of these could be expected to detect life, but they paved the way for the probes of the next few years.  Within a decade it ought to be possible to send a probe to Mars, collect material and bring it home for analysis in our laboratories.  Then, with any luck at all, we ought to find out whether Martian organisms have ever existed.  Just in case they have existed (or still do), the samples will be rigorously quarantined until they have been shown to be harmless, and I suspect that the first analyses will be carried out in space-craft.  Remember Professor Quatermass!

If any Martian life is found, it will be very lowly; there is no chance of anything so advanced as a blade of glass.  So why is its detection - or non-detection - so important?  One special reason occurs to me, and I have not seen it well emphasized before.  My question is this.  If life is possible elsewhere, can we assume that it will occur?  This is where Mars can give us the key.

The Sun is one of 100,000 million stars in our galaxy alone.  It is a very common sort of star, and there are many of just the same type; moreover we know of at least 1000 million galaxies, so that the total number of stars in the universe is unbelievably large.  Can we assume that our own, utterly undistinguished Sun, is the only one to be the centre of a planetary system?  This is surely absurd, and in any case we do now have strong indirect evidence of the existence of extra-solar planets.  Many of these must be similar to Earth, and therefore could support life.  What we do not know - yet - is whether life will automatically appear wherever conditions are suitable for it.

And herein lies the importance of Mars.  If Mars has ever supported life, no matter how lowly, it will go a long way toward proving that life merely awaits a suitable environment before gaining a foothold, and will evolve as far as it can before the conditions become too hostile.  If life can be shown to have appeared independently on two planets in the same system - Earth and Mars - then there must be a strong argument that life is widespread elsewhere too.

If no signs of life are found, the situation will be less clear-cut, and we cannot jump to conclusions by saying that life elsewhere is likely to be uncommon.  We will need further evidence; the jury will still be out.

I believe that this whole problem is more important than most people realize.  I am writing these words in November 1997, and at the moment I have a completely open mind.  Frankly, I hope that the probes of the next few years will show that Mars does, or once did, support primitive life, but in my view the chances are about 50-50.  Time will tell.

Patrick Moore