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Origin of the Moon's orbital inclination from resonant disk interactions

Nature volume 403, pages 741–743 (2000)Cite this article

Abstract

The Moon is generally believed to have formed from the debris disk created by a large body colliding with the early Earth1,2. Recent models of this process predict that the orbit of the newly formed Moon should be in, or very near, the Earth's equatorial plane3,4. This prediction, however, is at odds with the known history of the lunar orbit: the orbit is currently expanding, but can be traced back in time to reveal that, when the Moon formed, its orbital inclination relative to the Earth's equator was I ≈ 10° (refs 5, 6). The cause of this initial inclination has been a mystery for over 30 years, as most dynamical processes (such as those that act to flatten Saturn's rings) will tend to decrease orbital inclinations. Here we show that the Moon's substantial orbital inclination is probably a natural result of its formation from an impact-generated disk. The mechanism involves a gravitational resonance between the Moon and accretion-disk material, which can increase orbital inclinations up to ∼15°.

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Figure 1: The evolution of the Moon's orbit as it resonantly interacts with an inner impact-generated disk.
Figure 2: The Moon's initial orbital inclination.

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Acknowledgements

We thank L. Dones, D. Stevenson, G. Stewart and J. Wisdom for comments, and A. G. W. Cameron for data from his SPH impact simulations. This work was supported by NASA's Planetary Geology and Geophysics, and Origins of Solar Systems, Programs.

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  1. Southwest Research Institute, 1050 Walnut Street, Suite 426, Boulder, 80302, Colorado, USA

    William R. Ward & Robin M. Canup

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  1. William R. Ward
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Correspondence to William R. Ward.

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Ward, W., Canup, R. Origin of the Moon's orbital inclination from resonant disk interactions. Nature 403, 741–743 (2000). https://doi.org/10.1038/35001516

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