Observational Constraint on the Radius and Oblateness of the Lunar Core-Mantle Boundary (original) (raw)
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Abstract
Lunar laser ranging (LLR) data and Apollo seismic data analyses, revealed independent evidence for the presence of a fluid lunar core. However, the size of the lunar fluid core remained uncertain by ±55 km (encompassing two contrasting 2011 Apollo seismic data analyses). Here we show that a new description of the lunar interior's dynamical model provides a determination of the radius and geometry of the lunar core-mantle boundary (CMB) from the LLR observations. We compare the present-day lunar core oblateness obtained from LLR analysis with the expected hydrostatic model values, over a range of previously expected CMB radii. The findings suggest a core oblateness (fc=(2.2±0.6)×10-4) that satisfies the assumption of hydrostatic equilibrium over a tight range of lunar CMB radii (RCMB=381±12 km). Our estimates of a presently relaxed lunar CMB translates to a core mass fraction in the range of 1.59-1.77% with a present-day free core nutation within (367±100) years.
Publication:
Geophysical Research Letters
Pub Date:
July 2019
DOI:
arXiv:
Bibcode:
Keywords:
- Moon;
- hydrostatic fluid core;
- nonhydrostatic lithosphere;
- core-mantle boundary;
- free core nutation;
- LLR-GRAIL combination;
- lunar ephemeris;
- Physics - Geophysics;
- Astrophysics - Earth and Planetary Astrophysics;
- General Relativity and Quantum Cosmology
E-Print:
Accepted for publication in Geophysical Research Letters