VACANT LOTS IN THE SOLAR SYSTEM
 |
A Venus landscape might look something like this: an imaginary picture of the earth during the coal age. |
Is there life on other worlds than ours? More especially, is there intelligent life? Are there human beings, or any beings, whatever they may look like, with minds comparable to human minds? Do they wonder about us, as we wonder about them? Are they trying to get into communication with us, and will it ever do us any good to try to get into communication with them?
The natural inclination of most of us is to believe that there is life in other parts of the universe besides the little spinning globe to which we cling. We are all more or less unconsciously imbued with the dictum of the medieval schoolmen that "nature abhors a vacuum," and the notion that all these other worlds are quite empty strikes us as a sheer waste of good real estate. If they are really devoid of human life, we'd like to have the job of subdividing them and putting them on the market. Jules Verne, H.G. Wells and a whole host of other romancers have woven hundreds of fantastic tales about invasions of the earth from Mars, or voyages to the moon in a giant rocket.
But the other-world fairylands of renaissance and early modern speculation have been passed in review before the great unwinking eyes of our great telescopes, and one by one they have puffed and burst like rainbow-colored bubbles. Out of the eight planets that circle around the sun, to only one, our own earth, can we with any certainty assign a population of living plants and animals, ruled over by a human race. Two of the remaining seven, Mars and Venus, may conceivably support life, though there is no real evidence that they do. All the other planets, together with earth's satellite, the moon, are with hardly the shadow of a doubt totally devoid of any living thing.
Why are we so certain of this? Well, life of any sort demands certain conditions for its existence. There must be solid land for animals, water for fish, air for birds and insects. There must be oxygen for breath, carbon dioxide and nitrogen for plants to make into food, sunlight to supply the energy for this all-important process. The temperature must not drop below the freezing point of water for too long a time, nor rise above a certain limit, which for most plants and animals is well short of the boiling point. These are not all the necessary conditions, but only a few of the outstanding ones. If a planet can not offer all the necessary conditions, it goes uninhabited. If even one of them is lacking, the planet is just as badly off as if it offered none at all. Life is a very fussy tenant.
If we check over the list of planets with these considerations in mind, the outlook is not at all good for habitability of the houses in this part of the universe. The four outermost planets, Jupiter, Saturn, Uranus and Neptune, the giants of the solar system, are ruled out at once on several counts. For one thing, they are simply too big. The smallest of them, Uranus, has fifteen times the mass of the earth, while the largest, Jupiter, overtops us in weight of 318 times. The force of gravity on them of course is proportional to the mass, so that a man or any higher animal of the kinds we know would be crushed flat by his own weight if he landed on one of them. One could get some idea of how it would feel to be on one of these huge planets by putting on a suit of antique armor and trying to take a stroll across the face of one of the powerful electromagnets used in the steel mills for lifting carloads of pig iron.
Moreover, life at the visible surface of one of these planets would be impossible for anything but winged creatures able to remain constantly in the atmosphere; for what we see of these four giants is not the solid globe itself, but the outside of a very dense atmosphere. No one knows what this atmosphere is made of. Certainly, however, it is not transparent like air. It either contains gases much denser or more opaque than air, or is perpetually cloudy. The peculiar belted and striped appearance of Jupiter strongly suggests the latter possibility. How far down through this sea of gas it is to solid earth, or rather to solid Jupiter, again no one knows. Nor is it known what conditions would be like at the solid surface of one of these giant planets, if such a solid surface exists. Some astronomers guess that it might be very hot and others that it is very cold but they candidly state that these are only guesses.
copyright 1997 Science Service