What Mariner Really Saw

Man's age-old dream of extraterrestrial life was stimulated earlier this summer by preliminary interpretations of data sent back from Mars by the twin Mariner probes. Hurriedly examining the readings from his infrared spectrometer on board Mariner 7, Chemist George C. Pimental had dramatically announced that the Martian atmosphere probably contained traces of ammonia and methane, two gases produced on earth by bacterial decay. The implication was clear: there might well be micro-organisms on Mars.

Last week, after further study of the Mariner data, Pimental reported that his ephemeral clue to the existence of Martian life had proved to be false. What he had read as the characteristic "signatures" of methane and ammonia in spectrographic information gathered near the Martian south pole, he admitted, were actually produced by a thick layer of frozen carbon dioxide, otherwise called diy ice. How did the embarrassing error occur? Only when he checked out the experiment in his laboratory, Pimental explained, did he learn that a thick layer of dry ice could produce spectral characteristics similar to those of methane and ammonia.

Dry-Ice Clouds. Other scientists also had some second thoughts about their Mars findings. Originally, the temperature of the southern polar cap was reported as -180DEGF., or roughly the frost point of carbon dioxide under Martian atmospheric pressure. Now, the scientists say that the temperature is probably about four degrees lower and the atmospheric pressure several millibars higher than first estimated. That would mean that the pole is not solid carbon dioxide, as scientists once speculated. Instead, it is possibly composed of a mixture of carbon dioxide and ordinary ice, and perhaps obscured by a cloud of dry-ice particles.

Six weeks after the Mariner pictures were transmitted, scientists at Pasadena's Jet Propulsion Laboratory were also getting a far clearer look at the red planet itself. In the first fast playback of the 200 TV images radioed by the two probes, they saw a very rough and lunar-like surface. But after considerable electronic enhancement of the pictures, a slow process that increases contrasts and eliminates random "noise" in the radio signals, the scientists have now produced a portfolio of photographs that show three distinctly different types of Martian topography. Besides cratered regions, there are huge, flat, featureless areas like the 1,200-mile-long plain called Hellas. There are also vast expanses of jumbled, chaotic terrain, whose short ridges and small valleys are unlike any features on the moon and do not exist on so large a scale on earth. Concludes Caltech Geologist Robert Sharp: "Mars is definitely its own man."

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