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Title:
Mercury Interior Properties from Measurements of Librations
Authors:
Margot, Jean-Luc; Peale, Stanton J.; Jurgens, Raymond F.; Slade, Martin A.; Holin, Igor V.
Affiliation:
AA(California Institute of Technology), AB(University of California, Santa Barbara), AC(Jet Propulsion Laboratory), AD(Jet Propulsion Laboratory), AE(Space Research Institute)
Publication:
Mercury, 25th meeting of the IAU, Joint Discussion 2, 16 July, 2003, Sydney, Australia, meeting abstract
Publication Date:
00/2003
Origin:
IAU
Bibliographic Code:
2003IAUJD...2E..16M

Abstract

Peale (1976) showed that the measurement of four quantities (the obliquity of the planet the amplitude of its longitude librations and the second-degree gravitational harmonics) are sufficient to determine the size and state of Mercury's core. The nature of the core has profound implications for theories of planetary magnetic field generation and planetary thermal evolution.

Here we describe the successful implementation of a new Earth-based radar technique (Holin 1992) that provides spin state measurements with unprecedented accuracy. We observed Mercury with the Goldstone radar and the Green Bank Telescope near aphelion in May-June 2002 and near perihelion in January 2003. We illuminated the planet with a monochromatic signal recorded the scattered power at the two antennas and cross-correlated the echoes in the time domain. In all cases we obtained very strong correlations which directly constrain the instantaneous spin rate and orientation. Spin rate variations can be measured to 1 part in 100 000 or better while the spin rate signature expected from the longitude librations is roughly 1 part in 10 000.

We will present our measurements of the spin state and the longitude librations along with inferences about interior properties.

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