Farouk El-Baz

Document Type

Article

Publication Date

9-17-1974

Abstract

The Apollo mistions have gradually inereased our knowledge of the Moon's chemistry, age, and mode of formation of its surfiwe features and materials, Apollo li and landings proved that mare materials are valcanic rocks that were derived from deep-scated basaltie melts about 8,7 and 3.2 billion years ago, respee- tively. Later missions Providedl additional information on lunar mare basalts as well the older, anorthositie. highland pocks. Datn on the chemical make-up of returned samples iere extended 9), larger arens the Moon bY orbiting geo- chemical experiments, These have also mappodl inhomogeneities in hmar surface chemistry, including radionctive anomalies on both the noar and far sides. Lunar samples and photographs indicate that the moon is a well-preserved museum of ancient impaot sears. The crust of the Moon, which was formed about 46 billion years ago, was subjeeted to intensive metamorphism by large impacts. Although bombardment continues to the present day, the rate and size of impact- ng bodies were much groater in the first 0.7 billion years of the Moon's history. The last ofthe large. circular, nultiringed basins occurred about 3.9 billion years ago. These basins, many of which show positive gravity anomalies (mascons). were flooded by voleaaie basalts during period of at aast 600 million years. In addition to flling the eireular basins, more $O on the nearside than on the farside, the basalts also eovered lowlands and cireum-basin troughs. Profiles of the outer lunar skin were constructed from the mapping camera system,- including Ahe laser altimeter, and the radar sounder data. Materials of the eruet, aecording to the lunar seismie data. extend to the depth of about 65 ki on the near side, probable more OR the farside. The mantle which underlies thecrust probably extends to about 1100 km depth. It is also probable that a molten or par- tially molten gone or core underlies the mantle, where interaetions between both may eause the deep-seated moonquakes. The three basie theories of lunar origin--- capture, fission. andl binary aceretion are still eompeting for first piace. The last tobe the most popular the thre at this time; it requires the least nmber of assumptions in placing the Moon in Earth orbit and simply nccounts for the chemieal differenees bet weon the two bodies. Although the question of origin has not vet been resolved, we are besinning to see the value of interiseiplinary synthesis of Apollo scientitie returns. Durng the next few years we should begin to renp the frits of attempts at this synthesis. Then ie nar be fortnnnte enoueh tO fake nothes touk at the Moon from the proposed Lunar Polar Orbit (LPO) mission in about 1979.

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