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Science 4 August 2006:
Vol. 313. no. 5787, pp. 652 - 655
DOI: 10.1126/science.1128237
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Reports

Evidence for a Past High-Eccentricity Lunar Orbit

Ian Garrick-Bethell,* Jack Wisdom, Maria T. Zuber

The large differences between the Moon's three principal moments of inertia have been a mystery since Laplace considered them in 1799. Here we present calculations that show how past high-eccentricity orbits can account for the moment differences, represented by the low-order lunar gravity field and libration parameters. One of our solutions is that the Moon may have once been in a 3:2 resonance of orbit period to spin period, similar to Mercury's present state. The possibility of past high-eccentricity orbits suggests a rich dynamical history and may influence our understanding of the early thermal evolution of the Moon.

Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.

* To whom correspondence should be addressed. E-mail: iang{at}mit.edu

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Excitation of Lunar Eccentricity by Planetary Resonances.
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