Large impact craters and the moon's orientation |
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| Authors: | HJ Melosh |
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| Institution: | Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, Calif. USA |
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| Abstract: | This paper investigates the idea that large impact events have caused the moon to change its orientation in space. It is found that the very largest impact events, such as those which formed Imbrium and Orientale, probably did reorient the moon. This reorientation is primarily due to the change in the moon's moments of inertia consequent upon crater formation. The impulse delivered by the impact can at most unlock the moon's synchronous rotation for a few thousand years, and is thus not of major importance. The moon will attain its new orientation in less than a few times 104 years as a result of tidal friction. Since the large craters eventually are filled by isostatic rebound and extrusive igneous activity, the moon may eventually regain its original orientation unless other phenomena cause new changes in the distribution of mass on its surface. |
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