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No. 37: Jan-Feb 1985

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The puzzle of the moon's origin

The moon is the closest and best-studied astronomical object. Yet, there is no agreement as to its mode of origin. One might say that planetary scientists have just about thrown in the towel on the three major theories of lunar origin. Two recent articles attest to this discouraging situation.

A Sky and Telescope article provides an excellent review of all three theories, indicating the reasons why each fails to convince a majority of scientists. The theories and the primary reasons for their rejection are:

(1) Fission from earth. Lack of sufficient angular momentum in the earthmoon system and the fact that the moon does not orbit in the plane of the earth's equator. (2) Gravitational capture. The capture of such a large object in a nearly circular orbit is considered too improbable. (3) Earth-moon accretion as a double planet. The compositions of the earth and moon are too different.

This article concludes that the resolution of the problem of lunar origin must await our return to the moon for more scientific exploration.

(Rubin, Alan E.; "Whence Came the Moon?" Sky and Telescope, 68:389, 1984.)

An article in Science also discusses the classical theories of lunar origin and quickly disposes of them for the above reasons. However, a fourth theory makes an appearance, which we might call the Big Splash Theory. The idea is that a Mars-sized object (1/10 the earth's mass) made a grazing collision with the earth when the solar system was more heavily populated with debris. This collision vaporized the projectile's rocky mantle as well as a similar quantity from the earth. This material was flung into orbit by the force of the impact and the expanding hot gases. Beyond the Roche Limit, the expelled debris coalesced into the moon. This fourth theory is now seriously considered by planetary scientists who -- so far -- have found no serious defects.

(Kerr, Richard A.; "Making the Moon from a Big Splash," Science, 226:1060, 1984.)

From Science Frontiers #37, JAN-FEB 1985. 1985-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:


  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987