A Clear View of Mars

When Mariner 9 arrived in the neighborhood of Mars last November, its TV cameras were thwarted by the billowing yellow dust clouds of a gigantic storm that obscured most of the surface of the Red Planet. Frustrated scientists and controllers at Pasadena's Jet Propulsion Laboratory began to despair that their spacecraft would ever fulfill its primary mission: mapping the surface of Mars. But by mid-January the Martian skies had cleared, and Mariner began sending back detailed pictures. Last week NASA released the latest group of Mariner photographs. Transmitted across more than 100 million miles of space and clarified with the aid of a computer, they provided spectacular evidence that Mariner's mission has been a stunning success.

The photograph that has caused the most excitement among scientists shows a 250-mile-long valley that resembles an arroyo (a water-cut gulley common in semiarid regions on earth). The valley is 3 1/2 miles wide and has branching, streamlike tributaries that seem more likely to have been formed by water than by lava. "We are hard put to find a mechanism other than running water for these features," says Harold Masursky of the U.S. Geolog ical Survey. Although scientists agree that there is no free-flowing water on the Martian surface now, the sharp and uneroded features of the valley indicate that it could have been formed in the not-too-distant past--perhaps within the last million years.

Discovery of the valley has increased speculation that water-dependent forms of life may once have existed--or still exist--on Mars. That possibility has also been strengthened by readings from Mariner's instruments. They indicate that about 100,000 gallons of water vapor escape daily into space from the Martian atmosphere. Scientists believe that the vapor and carbon dioxide are being continually vented from volcanoes in the same kind of process that created the earth's early atmosphere.

Another remarkable group of photos looks straight down at the largest volcano ever seen by man, Nix Olympica, which is six miles high and more than 300 miles in diameter at its base. Evidence of the fury of Martian winds can be seen in a number of pictures that show tear-shaped features to the leeward side of craters and other surface irregularities. Scientists believe that these features are wind shadows of sand that are formed behind the craters by the violent winds. One photograph shows an area with unusual swirls, and a crater-like feature that to the hard-working JPL scientists seems to have definite feminine characteristics. The area has been named "Lascivious Lacus."

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