Science: Dust on the Moon

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If man-made spaceships ever reach the moon, many space enthusiasts assume that they will find suitable landing gronds on the moon's vast, level plains. This assumptions is based on the view that the lunar plains, which are made of some darker material than the rest of the moon's surface, are actually lava beds poured out from once-active volcanoes whose craters now it the moon's surface. Recent observations, however, suggest that the moon has been a cold planet for so long that volcanic activity is not a satisfactory explanation of its topography. Instead, the belief is growing that its craters were torn out by meteorites, and that the plains are huge seas of dust.

The principal exponent of this theory is Thomas Gold of Britain's Royal Greenwich Observatory, Cosmologist Gold recently developed his ideas for a British university audience. By measuring the size of the moon's craters, the slope of thier sides, and the distance to which debris has been dispersed around them, Gold concluded that they were scooped out by huge meteorites bombarding the moon from outer space at speeds of 112,000 m.p.h. At the point of impact, says Gold, the moon's surface rock must have been gasified at temperatures of up to 10,000,000°C. The accompanying explosions, he thinks, dug out the craters about the impact point, often leaving a small, punctured peak in the middle.

Gold believes htat dust and debris from the crater-building explosions filled in most of the older craters on the moon's surface. Since there is neither wind nor rain on the moon, the dust would stay more or less where it settled except when agitated by thermal or electrical disturbances. If such is the case, says gold, the dust could "flow over the surface like a liquid, running down the sides of cold craters to fill in the bottoms." Gold therefore believes that the moon's vast plains are not exposed layers of lava but oceans of fine-powdered dust that may be anything from 100 ft. to two miles in depth.

To test Gold's theories, a University of Manchester research team will shortly spend three months at the Pic du Midi observatory in the Pyrenees, measuring variations in the brightness of light on a selected section of the lunar flats. The amount of variation and polarization that occurs at different times of the lunar day will indicate whether the sun's rays are being scattered by tiny dust particles or by solid surface. "Within two or three months we should know definitely," says Professor Zdenek Kopal, who will take charge of the experiment. Meantime, says Cosmologist Gold, spaceship pilots are advised not to land on the lunar plains.