The Moon's Molten Core and Tidal Q

Details The Moon's Molten Core and Tidal Q The Moon's Molten Core and Tidal Q

Jan 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998stin...0058166w&link_type=abstract

Technical Report, Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA United States

Computer Science

Gravitational Fields, Laser Range Finders, Lunar Core, Lunar Prospector, Lunar Rotation, Moon, Periodic Variations, Radar Tracking, Boundaries, Distortion, Doppler Radar, Failure, Iron, Moments Of Inertia, Radii, Sensitivity, Signatures, Time Lag

Scientific paper

The rotation of the Moon is influenced by solid-body tides and interaction at a liquid-core/solid-mantle boundary. The Lunar Laser Ranging (LLR) data are sensitive to variations in lunar rotation. Analysis of those ranges reveals four dissipation periodicities in the rotation. These signatures can be explained with the combined effects of tide plus core, but not with either alone. The fluid core detection exceeds three times its uncertainty. The inferred core radius has a 1 -sigma upper limit of 352 km for iron and up to 374 km if sulfur is present. The tidal dissipation is strong, Q at one month is 37 +/- 5 .Q increases for longer periods and is 60 (-15, +40) at one year.Dynamical evidence for a fluid lunar core has previously been presented. These-earlier solutions included three dissipation parameters. New solutions benefit from additional LLR data and an improved gravity field from Doppler tracking of Lunar Prospector. Five dissipation parameters are now solved for. There are several options for dissipation parameters: a core coupling parameter, a time delay for tidal distortion of the moments of inertia, and five periodic terms in the rotation angles. Solutions with different combinations of these are compatible (a theory relates K/C and time delay to a series of periodic terms). The solutions used K/C, time delay, and one periodic term. When dissipation signatures at five rotation frequencies are solved for, four amplitudes (4 to 263 milliarcseconds) are detected above the noise. Attempts to explain these results using either tides alone or core alone fail (less than 3(sigma) discrepancy for the former and 9(sigma), for the latter). A combination of tides and liquid core matches the results well.

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