Water on the Moon

Had Surveyor 3 landed on the moon's Ocean of Storms some 4 billion years ago, it might have created an even bigger splash than it made last week. For early in lunar history, Nobel Laureate Harold Urey told the National Academy of Sciences last week, the moon may have had an atmosphere, rainfall, lakes and even oceans.

Unlike most scientists, Chemist Urey believes that water--not lava--formed the smooth lunar plains and filled-in depressions revealed in photographs taken by Ranger and Orbiter spacecraft. The dark plains, he says, "look precisely like the bottoms of dried-up, primitive oceans or lakes." And material in filled-in craters and crevices may once have been flowing mud.

Urey suggests that lunar water had a terrestrial origin. If the moon was torn from the earth, he says, it would have carried off substantial amounts of water. Or if, as Urey believes, the moon was a planetary interloper captured by the earth, its gravity would have attracted terrestrial water as well as solid matter during the cataclysmic events caused by its close approach to the earth.

Fascinating Possibility. The moon could not remain wet for long, says Urey. Because of weak lunar gravity, the water that evaporated during the moon's long, hot days would have escaped into space, along with the primitive atmosphere. Within a few thousand years after they had formed, Urey believes, the lunar waters dried up, before they could carve out major features such as valleys and stream beds similar to those formed by water flowing on earth. If any water remains on the moon today, he says, it is probably in the form of ice buried below the surface and insulated from solar heat. The gradual melting and vaporization of this ice, which would leave voids beneath the surface, may account for the cave-ins visible in moon-probe photographs.

Urey bases his wet-moon theory on far more than mere visual evidence. As he sees it, most of the earth's stony meteorites come from the moon, knocked off by other meteorites and occasional comets that have bombarded the lunar surface. Imbedded in many of those moon-sent meteorites are smooth fragments that appear to have been shaped by frictional effects like those that would be caused by flowing water. They also contain such minerals as clay-type silicates and calcium carbonates that Urey says "can hardly be accounted for except by the action of liquid water over some length of time."

The meteorites also contain carbon compounds that suggest an even more fascinating possibility. They could have been produced, says Urey, by primitive life forms that survived their violent passage from the earth and multiplied rapidly in the lunar waters during the few millenniums that the moon was wet.

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