Science: Mars Revisited

At first, the data sent back to earth by two Mariner spacecraft more than 60 million miles away seemed to offer as little hope as the lunar rocks that life would be found elsewhere in the solar system. Flying past the planet Mars, the small, instrument-packed spacecraft detected no evidence of nitrogen, an indispensable ingredient of life on earth. Probing the upper reaches of the Martian atmosphere, they failed to find anything like the ozone shield that protects the earth's surface from the sun's deadly rain of ultraviolet radiation. Even their stunning close-up photographs from only 2,200 miles above the red planet seemed to indicate that Mars is a cold, cratered globe, altogether inhospitable to life as man knows it.

Or is it? At week's end the infra-red spectrometer on board Mariner 7, the second of the two vehicles that flew past Mars, detected two gases—ammonia and methane—that could indicate the presence of primitive life. Both are produced on earth by biological decay. George C. Pimentel, a University of California chemist, said that he was unable to determine the amount of ammonia in the Martian atmosphere, but he estimated the concentration of methane as "no more than a few parts per million." In the earth's atmosphere, the amount is about 1.5 p.p.m.—and added rather jovially that among the terrestrial sources of methane are marsh gas and bovine flatulence, both of which result from the gradual deterioration of vegetable matter.

Biological Origin. Pimentel conceded that the gases he detected might have been produced on Mars by such nonbiological processes as "outgassing" from Mars' interior. But, he added, "One cannot restrain the speculation that the gases might be of biological origin." If that is the case, he theorized, they may have been produced by organisms that found shelter in a relatively hospitable ( —94°F.) region near the edge of Mars' southern polar cap, where Mariner 7 concentrated its cameras and instruments. There, he said, they might have drawn water from the polar ice and protection from the sun's ultraviolet radiation under a cloud of carbon-dioxide particles.

Other scientists at Pasadena's Jet Propulsion Laboratory (JPL) hotly dispute the idea that the polar caps are largely frozen water. Most investigators are now convinced that they are mostly frozen carbon dioxide, otherwise known as dry ice. Mariner 7 helped their argument. Its infra-red radiometer measured the temperature of the area at — 253°F., or roughly the frost point of carbon dioxide on Mars.

Even so, scientists are not quite ready to dismiss the possibility of life there altogether. Investigators think that microbes or other primitive forms of life may yet be discovered on Mars. In a number of studies, biologists have already shown that algae, plant seeds and even beetles can survive temperatures similar to those found on the red planet. "Considering the extreme conditions that organisms tolerate here on earth," adds the University of Hawaii's Sanford Siegel, a physiologist whose studies on low-temperature life have been supported by NASA, "I would be very surprised indeed if we didn't find life on other planets."