Changing the Lunar Image

Technicians were swarming around Launch Complex 39A at Cape Kennedy last week getting ready for the month-end lift-off of Apollo 14. But all the attention at Houston's Manned Spacecraft Center was still focused on the scientific byproducts of man's last successful moon landing. After painstakingly analyzing the 75.6 Ibs. of rock and debris hauled back from the edge of the Ocean of Storms by the Apollo 12 astronauts more than a year ago, 714 scientists gathered for NASA's second major moon-rock conference. The moon, they agreed, is not a cold, unchanging conglomerate of material, as originally suspected by some theorists. It is apparently still warm inside, has been geologically active and may even be undergoing small surface changes.

Crustal "Kreep." Perhaps the most direct evidence for this modern image of the ancient moon was the discovery of tiny, glassy bits of material in the Apollo 12 soil. Until a few weeks ago, lunar scientists had identified only fragments of lunar surface material, scraps of the moon's churned-up "topsoil." But Paul Gast, chief lunar scientist of the Manned Spacecraft Center, and other investigators seemed convinced that in the Apollo 12 samples they have now found chips from the moon's original underlying crust, which were apparently tossed up by the impact of a large meteorite.

Gast dubbed the suspected crust material "kreep," an acronym based on its unusually rich concentration of potassium (chemical symbol: K), rare-earth elements and phosphorus (P). The high concentration of these elements, in addition to large percentages of uranium, helped convince scientists that kreep originated during a melting process that would have produced a lunar crust. Kreep also has remarkable chemical and physical similarities to a 3-oz. lemon-size Apollo rock that Caltech's Gerald J. Wasserburg had previously calculated to be 4.4 billion years old, or about a billion years older than most of the other Apollo 11 and 12 rocks.

If there is indeed a lunar crust, the moon, like the earth, must have gone through a process of geological evolution known as differentiation. This would mean that the moon was once hot and fluid enough to have separated into layers of different density and chemical composition, the heavier metals sinking toward the lunar center, the lighter ones forming the crust.

Another indication that the moon is differentiated came from data radioed back to earth by the magnetometer left behind by the Apollo 12 astronauts. The magnetometer measures changes in the magnetic field induced in the moon by the solar wind, the charged particles that stream outward from the sun. Because the magnetometer's readings also offer clues to the moon's internal electrical conductivity and temperature, they enabled Dr. Charles Sonett of NASA's Ames Research Center to make an educated guess about the structure of the lunar interior.

As Sonett and other investigators see it, the moon has a core about 1,740 miles in diameter. Unlike the earth's core, it is probably not molten and never has been; Sonett thinks that it consists of rock similar to earthly olivine, which is rich in iron and is also found in meteorites. Around the core is a 60-mile-thick transition zone, or lower mantle, composed of a mixture of olivine and basalt-like rock that was apparently formed out of molten material. Next comes the 150-mile-thick upper mantle, an entirely basaltic layer in which, some lunar scientists suspect, there may have been slow-moving convection currents --movements roughly akin to those that occur in a simmering pot of oatmeal.

The crust itself is probably relatively thin. But during differentiation, the tug of terrestrial gravity would probably have pulled more dense material to the side of the moon facing the earth. As a result the crust there would have been slightly squeezed and become thinner than that on the far side. Indeed, such an uneven distribution of crust was offered by University of Chicago Mineralogist Joseph Smith to explain the paucity of maria on the far side. These great lunar seas are believed to be vast upwellings of lava, perhaps from volcanic eruptions set off by the moon's collision with large asteroids. On the far side, where the crust is thicker, such impacts would have been less likely to penetrate the moon's hard crust and release underlying lava.

The scientists, in any case, agreed that the maria are probably quite alike, a view supported by the first Russian scientist to attend a NASA moon conference. Reporting on the 3 oz. of dust gathered last September from the Sea of Fertility by the automated Soviet moon probe, Luna 16, Geochemist Aleksandr Vinogradov indicated that the dark gray samples were very similar to the American lunar specimens from the Ocean of Storms and the Sea of Tranquility, Apollo 11 's landing site. He elicited even greater interest with his revelation that the Russians are planning still more sophisticated unmanned retrievers; some will try to pick up samples from the geologically tantalizing highlands, probably the moon's oldest surface features.

Lunar Gardening. The moon's "topsoil" also produced some surprises. Examining a 16-in.-long lunar core obtained by the astronauts when they sank a tube into the surface of the moon, lunar scientists found ten distinctly different layers of material. This indicates that the churning and pulverizing effect --the so-called gardening of the lunar surface attributed to bombardment by smaller meteorites--is occurring in at least some places at a much slower rate than had been supposed, thereby allowing the various layers to accumulate undisturbed for long periods of time. Cracked University of Chicago Chemist Edward Anders: "Whoever is in charge of the gardening of the moon is not doing a very good job."

As expected, the lunar rock showed no indication of any life or concentrations of organic compounds. "This is the cleanest stuff you can find anywhere," commented the University of Bristol's Geoffrey Eglinton, one of 79 foreign participants at the conference. Nor did anyone find any trace of water--past or present; this prompted one scientist to comment that the moon was a million times as dry as the Gobi Desert.

There were new insights about the moon from another source: Apollo 12's highly sensitive seismometer, which has been recording a series of moon-quakes about once a month. Columbia University's Gary Latham traced the disturbances to an area of lunar rilles, or breaks in the lunar surface, near Fra Mauro, 120 miles to the east. Latham is convinced by the seismic evidence that the rilles, which look like dried-out river beds, are actually faults, "great cracks in the moon along which movements are presently taking place." He quickly added, however, that quakes are so small that they will present no danger to the Apollo 14 astronauts when they visit the rugged area around the crater Fra Mauro. Even if one of them stood within 50 ft. of such a quake, Latham said, he would barely feel it through his boots.

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