Is There Life on Mars --or Earth?

The seemingly barren surface revealed by Mariner 4's remarkable photographs last July dashed the hopes of many scientists that some form of life may exist on Mars. But their pessimism may be premature. At the annual meeting of the American Association for the Advancement of Science in Berkeley last week, Harvard Astronomer Carl Sagan suggested that a Martian version of Mariner 4 would have transmitted equally discouraging pictures of the Earth. "Had the Mariner 4 vehicle passed the same distance from the Earth that it did from Mars (6,000 miles) and obtained 22 comparable photographs," Sagan declared, "no sign of life on our planet would have been uncovered."

Nearsighted Satellites. Sagan's assumption is based on a study of photographs transmitted by NASA's weather-watching Nimbus and Tiros satellites. Those pictures were taken from as close as several hundred miles above the Earth and are somewhat clearer than the Mariner shots, which could not distinguish objects smaller than three miles in diameter. Though Sagan examined hundreds of them for signs of life on Earth, he could find none at all.

No sign of the vast highway networks, bridges, dams, or even cities on Earth could be found on the photos, said Sagan. Even differences in shading caused by seasonal changes in vegetation were difficult to detect, although many of the pictures were taken months apart. Concluded Sagan: the Mariner 4 pictures neither prove nor disprove the possibility of life on Mars.

Happily joining the debate last week, another scientist at the A.A.A.S. meeting declared that the Mariner pictures do suggest the possibility of Martian life. New Mexico State University Astronomer Clyde Tombaugh, who discovered Pluto in 1930, said that the faint markings on seven of Mariner's 22 photographs coincide with the controversial and elusive "canals" and "oases" that he and others have mapped in telescopic observations of Mars.

Melting Martian Frost. Tombaugh found that the largest crater in the best Mariner photograph is located where visual observations have spotted an oasis. Parallel markings in the southern part of the crater coincide with the position of a short canal mapped by Astronomer Percival Lowell in 1894.

Tombaugh believes that the canals are faults or fractures, several miles wide, in the Martian crust. Their darkening and fading may be caused, he says, by the intermittent escape of hot gases that melt a thin layer of frost and vegetation. The oases where the faults intersect, he speculates, are probably impact craters where moisture gathers and promotes the growth of moss or lichenlike plants hardy enough to withstand the harsh Martian climate.

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