The moon after Apollo

The Apollo missions have gradually increased our knowledge of the Moon's chemistry, age, and mode of formation of its surface features and materials Apollo 11 and 12 landings proved that mare materials are volcanic rocks that were derived from deep-seated basaltic melts about 3.7 and 3.2 billion years ago, respectively. Later missions provided additional information on lunar mare basalts as well as the older, anorthositic, highland rocks. Data on the chemical make-up of returned samples were extended to larger areas of the Moon by orbiting geochemical experiments. These have also mapped inhomogeneities in lunar surface chemistry, including radioactive anomalies on both the near and far sides.Lunar samples and photographs indicate that the moon is a well-preserved museum of ancient impact scars. The crust of the Moon, which was formed about 4.6 billion years ago, was subjected to intensive metamorphism by large impacts. Although bombardment continues to the present day, the rate and size of impacting bodies were much greater in the first 0.7 billion years of the Moon's history. The last of the large, circular, multiringed basins occurred about 3.9 billion years ago. These basins, many of which show positive gravity anomalies (mascons), were flooded by volcanic basalts during a period of at least 600 million years. In addition to filling the circular basins, more so on the near side than on the far side, the basalts also covered lowlands and circum-basin troughs.Profiles of the outer lunar skin were constructed from the mapping camera system, including the laser altimeter, and the radar sounder data. Materials of the crust, according to the lunar seismic data, extend to the depth of about 65 km on the near side, probably more on the far side. The mantle which underlies the crust probably extends to about 1100 km depth. It is also probable that a molten or partially molten zone or core underlies the mantle, where interactions between both may cause the deep-seated moonquakes.The three basic theories of lunar origin—capture, fission, and binary accretion—are still competing for first place. The last seems to be the most popular of the three at this time; it requires the least number of assumptions in placing the Moon in Earth orbit, and simply accounts for the chemical differences between the two bodies. Although the question of origin has not yet been resolved, we are beginning to see the value of interdisciplinary synthesis of Apollo scientific returns. During the next few years we should begin to reap the fruits of attempts at this synthesis. Then, we may be fortunate enough to take another look at the Moon from the proposed Lunar Polar Orbit (LPO) mission in about 1979.