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Optical Canals. Mars is more interesting than Venus because its atmosphere is transparent enough to permit its surface to be seen. But astronomers do not agree about what they see on it. All of them see white patches at the planet's poles, which they accept as thin layers of ice or hoarfrost. All of them see irregular light and dark markings that change with the Martian seasons. Only a few of them still see the network of straight, artificial-looking lines that was widely believed a generation ago to be a system of irrigation canals built by highly civilized beings to distribute the failing water supply of their aging planet.
Even stern astronomers regret to see the Martians abolished, but they can do nothing to save them. They have to insist that even if Mars is really covered with fine lines at the limit of vision, they cannot be irrigation canals, since they are not arranged in a way that would distribute water from the icecap, and they follow no logical contour lines. With this notion lost, there is no further support for the civilized Mars theory.
The Martian atmosphere is thin (8% of the pressure on earth) and may have no oxygen. It contains a little carbon dioxide and probably nitrogen and argon. The daytime temperature may occasionally rise above 86° F., and at night it may fall to minus 150° F.
These are tough conditions for life, but life is tough. Mars's seasonal changes of color suggest strongly the growth of something like vegetation in the Martian spring when the polar icecap melts or evaporates and spreads its scanty moisture over the nearby surface. And only this year new evidence was found that some kind of life exists on Mars—perhaps at the level of lichens. Dr. William M. Sinton of Lowell Observatory took spectrograms of Mars in infra-red light, found dips in three places where infra-red waves are absorbed by chemical compounds containing hydrogen atoms bonded to carbon. Earth's living plants and animals are made almost entirely of such compounds.
Small Star. There is little chance that life as known or imagined on earth can exist on any other solar system planet. Mercury is so close to the sun that its sunlit side (it always shows the same face to the sun) is hotter than molten lead. Its dark side, which gets no heat except from the stars and distant planets, is probably the coldest place in the solar system, only a few degrees above absolute zero ( — 273° C.).
Jupiter, the biggest planet, has a turbulent atmosphere thousands of miles deep made of unpleasant gases like hydrogen, methane and ammonia. In its upper levels float clouds of ammonia crystals. Jupiter is marked with conspicuous bands roughly parallel to its equator. They may be storm belts, but no one really knows. A great oval red spot about 25,000 miles long in its southern hemisphere is unexplained. Dr. Kuiper thinks that the great planet is exceedingly hot inside ("really a small star") and that it has a peculiar surface made of solid hydrogen. Gigantic volcanoes bursting from below may send shock waves through the atmosphere, stirring it into raging storms and inducing great electrical discharges.