The Lighthearted Moon

The clear pictures televised from Ranger spacecraft have brought man closer and closer to the surface of the moon. But for an advanced step in lunar explorations--a first comparison between the moon's crust and its invisible interior--scientists have now abandoned telescope and camera and turned to the computer.

Resetting the Clock. Columbia University Astronomer Wallace J. Eckert and Graduate Student H. F. Smith Jr. of IBM's Watson Laboratory at Columbia began by analyzing the moon's orbit with IBM's fast-figuring computers. The moon's position has been observed with precision for 200 years, so there was more than enough data to feed into the machines. After they pondered electronically for several hundred hours, weighing the effects of the earth, sun, planets and relativity on the moon's orbit, the computers reported that in a three-year cycle the moon would move ahead and then back of its previously calculated position by 440 ft. This minute exactness is important to scientific timekeepers, who sometimes use the moon as a standard clock. The calculations, in fact, corrected the moon clock by 0.2 sec. per year.

But even after this improvement, the new lunar calculations did not picture the moon behaving as expected. The plane of its orbit around the earth intersects the plane of the earth's orbit around the sun at points (nodes) that move through 360DEG about six times per century. The chief cause of this lunar shift is the pull of the sun's gravitation, but there are other influences too, and when all the known effects had been cranked into the equations, a discrepancy of 25 sec. of arc (.007DEG) per century still persisted.

Ingenious Theory. What was missing from the mathematical calculations, Dr. Eckert thinks, is a vital assumption: the moon has no heavy core like the earth's. Instead, it must have a heavy shell with lighter material inside. This would make the moon more reluctant to turn on its axis, and the extra resistance would account for its computer-calculated shift of orbit.

Dr. Eckert does not claim to know how the moon became lighthearted. One possibility is that it was originally formed of rather light rock that froze and became rigid, perhaps entrapping gases deep below the surface. Then, during two or three billion years, meteors rained on its surface, building up a thick layer of iron and other heavy materials. The truth of this ingenious theory will not be susceptible to a final check until a seismograph set by man on the moon's surface studies its interior by means of moon-quake waves.

This file is automatically generated by a robot program, so reader's discretion is required.