Past orientation of the lunar spin axis
- PMID: 17840827
- DOI: 10.1126/science.189.4200.377
Past orientation of the lunar spin axis
Abstract
The orientation of the lunar spin axis is traced from the early history of the earth-moon system to the present day. Tides raised on the earth by the moon have caused an expansion of the lunar orbit. Tides raised on the moon by the earth have de-spun the moon to synchronous rotation and driven its spin axis to a Cassini state-that is, in a coprecessing configuration, coplanar with the lunar orbit normal and the normal to the Laplacian plane (which is at present coincident with the normal to the ecliptic). This combination of events has resulted in a complex history for the lunar spin axis. For much of the period during which its orbital semimajor axis expanded between 30 and 40 earth radii, the obliquity of the moon was of order 25 degrees to 50 degrees . In fact, for a brief period the obliquity periodically attained a value as high as 77 degrees ; that is, the spin axis of the moon was only 13 degrees from lying in its orbit plane.
Comment in
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Tidal evolution of the Moon from a high-obliquity, high-angular-momentum Earth.Nature. 2016 Nov 17;539(7629):402-406. doi: 10.1038/nature19846. Epub 2016 Oct 31. Nature. 2016. PMID: 27799656
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