Text 02 -- IS THERE LIFE ON THE PLANETS
Text 2
IS THERE LIFE ON THE PLANETS?
During this Month 1all the five planets which can be seen with the naked eye are visible. Venus is an evening star, setting about an hour and a half after the sun. Jupiter is the brightest star in the sky after Venus has set, and Saturn is to be seen to the east of Jupiter. If you go to work in the morning before daybreak, you may see Mercury and Mars in the east, rising before the sun.
What are these planets? Many primitive people thought they were gods, and controlled human destiny 2. Their reasons seem to have been something like this. The fertilising flood of the Nile comes just after Sirius is first visible in the morning. So Sirius controls the Nile flood. And in the same way another star controls the lambing season 3 and a third the wheat harvest.
But some events, such as wars and pestilences 4, do not happen regularly. So they must be controlled by the stars which move their position relative to the others, the planets or wanderers. This argument is no worse than many which we now hear about the causes of wars and slumps. Even two thousand years ago, though the Greeks and Romans did not usually worship the stars, they thought it blasphemous 5 to suggest that heavenly bodieswere made of the same sort ofstuff as earthly things.
It had long been clear that the moon shines by reflected sunlight. When Galileo turned his telescope on Venus he saw a crescent 6 like the moon's, which altered its shape as the planet moved. It was therefore clear that the planets are cool bodies like the earth. Copernicus' theory that the planets and the earth went round the sun made it possible to calculate their distances, and their sizes were then determined by measuring their images in a telescope. Venus and Mars turned out to be about as big as the earth, Mercury somewhat smaller, and Jupiter and Saturn much bigger.
It seemed natural to speculate that they were inhabited. But before it was possible to say whether life as we know it could exist on the planets, a lot more information was needed. And our knowledge of the planets has not increased very greatly in the last fifty years, although we have found out vastly more about the distant stars and nebulae.
The reason is interesting. If we want to know more about a distant cluster of stars, we train a telescope on it, and use very complicated machinery and a still finer human control so that the telescope follows the cluster in its apparent motion across the sky. We then take a time exposure lasting for many hours.
But we cannot photograph the surface of Mars in this way, because the planet turns on its axis about as quickly as the earth. So astronomers must rely on their eyes. And as a matter of fact some of the best observation of the planets is done by amateur astronomers, including Mr. Will Hay, the comedian, and several English country clergymen, using relatively small telescopes.
It is clear that we can see the solid surface of Mars, whereas in the case of Jupiter, and probably Venus and Saturn, we can only observe the tops of clouds, which may consist of drops of liquid, or of solid dust. We can follow seasonal changeson Mars. During the winter each pole develops a white cap which doubtless consists of frost. This frost may be frozen water. But it may be solid carbon dioxide, which is used in the refrigerating industry under the name of dry ice, and is only solid at temperatures far below the freezing point of water. There are also colour changes elsewhere which may be due to vegetation.
Although we have not learned much fresh about the surface markings of these planets in the last fifty years, they have been studied with two instruments which tell us a lot about them. A sensitive thermopile placed at the focus of a telescope gives an electric current proportional to the heat corning from a star. Reflected sunlight is not stopped by a thin layer of water. But heat from a body which is warm, but not white-hot or even red-hot, is stopped. So by putting a little water bath in front of the thermopile we can measure the temperature of the planets.
Mercury and Venus are hotter than the earth, but Venus is probably well below the boiling point of water. On the other hand Mars is colder, though at least in the daytime inits tropics ice would melt. But the visible surfaces of Jupiter and Saturn are intensely cold, though the solid surface under the clouds may be somewhat warmer, especially if there are volcanoes.
We can also use the spectroscope. When light is passed through carbon dioxide certain components of it are absorbed. Not visible light (or carbon dioxide would be coloured), but infra-red light, which can be photographed on a specially sensitised plate. The same is true for other gases. So by comparing sunlight reflected by Venus with sunlight reflected from the moon, we can see that the former has passed through the equivalent of several hundred yards of pure carbon dioxide at the ordinary pressure.
And there is no oxygen or water vapour in the atmospheres of Venus or Mars, or at any rate far less than on Earth. Hence a man could only live on these planets in something like a mine rescue apparatus, and it seems to me a little unlikely that there is life of any sort on Venus. If there is life on Mars it is probably more like that of the bacteria which live without oxygen in black mud than to those of familiar animals and plants. So perhaps we had better make our own planet fit for rational beings before we colonise others.
1940
Література
John B.C. Haldane. Reader of Popular Scientific Essays. - Изд-во«Наука», М., 1993. - 235 с.