Astronomy: Lunar Lava Flow

Ever since Ranger 7 shot its closeups of the moon, scientists have been studying the pictures in minute detail. They contain the most detailed information man has ever collected about his planet’s nearest neighbor. And they are already shattering some long-held theories. Ranger’s lunar snapshots, says Dr. John A. O’Keefe of Goddard Space Flight Center, prove that the moon has not been a dead cinder ball for billions of years, as many astronomers believe. In fairly recent times, it seems to have stirred with volcanic activity.

The best Ranger photographs, explained O’Keefe in teh magazine Science, show a region covered by broad, light-colored streaks radiating from the craters Copernicus and Tycho. These rays are believed to be dust and fragments tossed out by teh meteor impacts that blasted the two craters, and since they lie on top of most other lunar features, they are listed among the youngest parts of the moonscape. But O’Keefe also found a conspicuous black mark showing starkly against the lighter background of one of Tycho’s rays. The ray had not dusted the mark with light-colored material — circumstantial evidence that suggests the mark must be more recent than the meteor impact that formed Tycho’s crater. Dr. O’Keefe noticed, too, that the mark is in line with set of ridges called wrinkles. Since these are all reasonably parallel, they cannot come from random meteor impacts but are probably of internal origin like the parallel ridges of many earthly mountains.

Dr. O’Keefe has concluded that the arėtes are volcanic, are probably made of stiff lava forced out of parallel cracks in the moon’s crust. Some of them may have erupted during the moon’s youth. Much more recently — 100 million years ago or less — one of the cracks may have opened agan and oozed laval to form a cluster of low black mounds on a plain that was already thickly peppered with debris from young Tycho.