Learn about the possibility of life on Mars

The idea that life can or even does exist on Mars has a long history. In 1877 the Italian astronomer Giovanni Schiaparelli claimed to have seen a planetwide system of channels. The American astronomer Percival Lowell then popularized these faint lines as canals and held them out as proof of a vast attempt by intelligent beings to irrigate an arid planet. Subsequent spacecraft observations have shown that there are no canals on the planet, and various other alleged proofs of life on Mars have turned out to be equally illusory. Not only are there no canals, but dark areas once thought to be oases are not green, and their spectra contain no evidence of organic materials. The seasonal changes in the appearance of these areas are not due to any vegetative cycle, but to seasonal Martian winds blowing sterile sand and dust. Water probably occurs only as ice on or below the surface or as trace amounts of vapor or ice crystals in the atmosphere. The strongest evidence against the presence of life, however, is the thinness of the atmosphere and the fact that the surface of the planet is exposed not only to lethal doses of ultraviolet radiation but also to the chemical effects of highly oxidizing substances (such as hydrogen peroxide) produced by photochemistry.

Perhaps the most fundamental and far-reaching result obtained by the Viking landers is that the soil contains no organic material (there is no reason to assume that the two landing sites are not representative of Mars). Although small amounts of organic molecules are continually being supplied to the surface of Mars by carbonaceous meteoroids, apparently this material is destroyed before it has a chance to accumulate. The results of the soil analysis for organic molecules carried out by the Viking landers provide no evidence for the existence of life.

A more difficult question is whether life ever existed on Mars, given the strong evidence of climatic change and the indications of a previously warmer, thicker atmosphere. Answering this question will probably involve collecting carefully selected subsurface samples and returning them to earth for detailed analysis. U.S. National Aeronautics and Space Administration has proposed a manned voyage to Mars early in the 21st century.