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GEOPHYSICAL RESEARCH LETTERS, VOL. 26, NO. 19, PAGES 3045–3048, 1999

Lunar Orbital Evolution: A Synthesis of Recent Results

Bruce G. Bills

Scripps Institution of Oceanography, La Jolla, California

Richard D. Ray

Space Geodesy Branch, NASA GSFC, Greenbelt, Maryland

Abstract

The present rate of tidal dissipation in the Earth-Moon system is known to be anomalously high, in the sense that the implied age of the lunar orbit is only 1.5 × 10⁹ years, though other evidence suggests an age closer to 4 × 10⁹ years. To assess how long the anomalous dissipation has persisted, we use published estimates of lunar orbital configurations derived from (a) fine grained sediments containing tidal laminations and (b) numerical ocean models averaged over varying ocean geometries. The implied histories of the lunar semimajor axis are surprisingly consistent over the past 10⁹ years. The ocean models imply, on average, reduced dissipation in the past because of a spatial mismatch between tidal forcing and oceanic normal modes of higher frequencies. Webb’s ocean model suggests that the “anomalous” oceanic dissipation began about 10⁹ years ago and has been increasing since then.

Received 19 April 1999; accepted 16 July 1999.

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Citation: Bills, B. G., and R. D. Ray (1999), Lunar Orbital Evolution: A Synthesis of Recent Results, Geophys. Res. Lett., 26(19), 3045–3048.

This paper is not subject to U.S. copyright. Published in 1999 by the American Geophysical Union.