Publication Date:
2014-06-13
Description:
The Gravity Recovery and Interior Laboratory (GRAIL) mission has sampled lunar gravity with unprecedented accuracy and resolution. The lunar GM , the product of the gravitational constant G and the mass M , is very well determined. However, uncertainties in the mass and mean density, 3345.56 ± 0.40 kg/m 3 , are limited by the accuracy of G . Values of the spherical harmonic degree-2 gravity coefficients J 2 and C 22 , as well as the Love number k 2 describing lunar degree-2 elastic response to tidal forces, come from two independent analyses of the 3-month GRAIL Primary Mission data at the Jet Propulsion Laboratory and the Goddard Space Flight Center. The two k 2 determinations, with uncertainties of ~1%, differ by 1%; the average value is 0.02416 ± 0.00022 at a 1-month period with reference radius R = 1738 km. Lunar Laser Ranging (LLR) data analysis determines ( C–A )/ B and ( B–A )/ C , where A 〈 B 〈 C are the principal moments of inertia; the flattening of the fluid outer core; the dissipation at its solid boundaries; and the monthly tidal dissipation Q = 37.5 ± 4. The moment of inertia computation combines the GRAIL-determined J 2 and C 22 with LLR-derived ( C–A )/ B and ( B–A )/ C . The normalized mean moment of inertia of the solid Moon is I s / MR 2 = 0.392728 ± 0.000012. Matching the density, moment, and Love number, calculated models have a fluid outer core with radius 200–380 km, a solid inner core with radius 0–280 km and mass fraction 0–1%, and a deep mantle zone of low seismic shear velocity. The mass fraction of the combined inner and outer core is ≤1.5%.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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