Vertical angular momentum constraint on lunar formation and orbital history

The Moon likely formed in a giant impact that left behind a fast-rotating Earth, but the details are still uncertain. Here, we examine the implications of a constraint that has not been fully exploited: The component of the Earth–Moon system’s angular momentum that is perpendicular to the Earth’s or...

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Published inProceedings of the National Academy of Sciences - PNAS Vol. 117; no. 27; pp. 15460 - 15464
Main Authors Tian, ZhenLiang, Wisdom, Jack
Format Journal Article
LanguageEnglish
Published Washington National Academy of Sciences 07.07.2020
Subjects
Angular momentum
Earth motion
Earth orbits
Earth orientation
Earth rotation
Lunar composition
Lunar orbits
Moon
Orbital resonances (celestial mechanics)
Physical Sciences
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Summary:The Moon likely formed in a giant impact that left behind a fast-rotating Earth, but the details are still uncertain. Here, we examine the implications of a constraint that has not been fully exploited: The component of the Earth–Moon system’s angular momentum that is perpendicular to the Earth’s orbital plane is nearly conserved in Earth–Moon history, except for possible intervals when the lunar orbit is in resonance with the Earth’s motion about the Sun. This condition sharply constrains the postimpact Earth orientation and the subsequent lunar orbital history. In particular, the scenario involving an initial highobliquity Earth cannot produce the present Earth–Moon system. A low-obliquity postimpact Earth followed by the evection limit cycle in orbital evolution remains a possible pathway for producing the present angular momentum and observed lunar composition.
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Reviewers: R.M.C., Southwest Research Institute; and S.T., Institute for Advanced Study.
Author contributions: Z.T. and J.W. designed research, performed research, analyzed data, and wrote the paper.
1Z.T. and J.W. contributed equally to this work.
Contributed by Jack Wisdom, May 4, 2020 (sent for review February 25, 2020; reviewed by Robin M. Canup and Scott Tremaine)
ISSN:0027-8424
1091-6490
1091-6490
DOI:10.1073/pnas.2003496117