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Venus is the nearest of the major planets to Earth and almost the same size. Its diameter is 7,700 miles against Earth's 7,927 miles. Venus has a dense atmosphere; its surface is constantly veiled by clouds. But the spectroscope discloses that Venus' atmosphere is largely composed of carbon dioxide; there is no discernible oxygen. Animal life could hardly get a foothold in such an environment. If there were vegetable life, it would have converted some of the carbon dioxide into oxygen. Dr. Jones considers that Venus is more or less in Earth's condition of a billion or so years ago, that it is still too hot there for life to get started. He believes that when the sun's heat output has dwindled, life on Venus may get under way.
If, biologically speaking, Venus appears much younger than Earth, then Mars appears much older. It is smaller and colder than Earth, has lost most of its atmosphere and water. But a thin atmosphere it still has, perhaps containing a little oxygen. And Mars has a little water, as the white polar caps show. These caps melt in the Martian summer, accumulate again in winter. The excitement over possible Martian inhabitants was started in the 19th Century by the Italian astronomer Schiaparelli, who described hazy streaks on the surface, called them canali. This Italian word means "channels," was erroneously translated "canals," which connotes intelligent engineering.
The canali do not show up clearly in photographs, because the photographic image of the planet is so small that a time exposure is necessary, and the turbulence of the earth's atmosphere then blurs the detail. The streaks show up better to visual observation, but observers disagree on what they see.
Modern consensus, says Astronomer Jones, is that the markings are not canals but natural formations of some sort. So the existence of intelligent beings, or even of any animal life, on Mars is still anybody's guess. If there are any Martian creatures, they must have adapted themselves to a very slow rate of oxygen intake. But all observers agree that there are distinct seasonal changes in some of the Martian markings. Certain dark areas are green in summer, grey or brown in winter. It is hard to conceive that these changes could be caused by anything but vegetation. And there, at last, is good evidence of life on another world.
Might there be life on other planets too far away for astronomy to find? In the visible universe there are about 100,000,000 other star-clouds like the Milky Way. If in each of these, on the average, there is one star with planets, that makes several hundred million planets. Many of these must be too hot or cold, too big or little, or lack suitable atmospheres and moisture. But on some, by the sheer law of averages, the conditions should be favorable for life. Astronomer Jones believes that where the conditions are favorable, life will arise. He believes that life is widely but thinly spread through the universe.
* The London wartime blackouts have aided Greenwich astronomers by cutting out the glow of city lights which interfered with telescope observation—but, presumably, the big fires set during mass raids have been a nuisance. Before the war there was serious talk of moving the observatory to another and darker site. Up to last week the observatory had not been hit and work was proceeding normally.