Journal Article

Core–mantle interactions for Mercury

B. Noyelles, J. Dufey and A. Lemaitre

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 407, issue 1, pages 479-496
Published in print September 2010 | ISSN: 0035-8711
Published online August 2010 | e-ISSN: 1365-2966 | DOI:
Core–mantle interactions for Mercury

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Mercury is the target of two space missions: MESSENGER (NASA), orbit insertion of which is planned for 2011 March, and ESA/JAXA BepiColombo, which would be launched in 2014. They will observe the surface of the planet with high accuracy (about 1 arcsec for BepiColombo), and this will encourage further study its rotation. Mercury is assumed to be composed of a rigid mantle and a partially molten core. We study the influence of the core–mantle interactions on the rotation perturbed by the solar gravitational interaction by modelling the core as an ellipsoidal cavity filled with inviscid fluid of constant uniform density and vorticity. We use both analytical (Lie transforms) and numerical tools to study this rotation with different shapes of the core. We stress on, in particular, the proper frequencies of the system, because they characterize the response of Mercury to the different solicitations, due to the orbital motion of Mercury around the Sun. We show that, contrary to its size, the shape of the core cannot be determined from observations of either longitudinal or polar motions. However, we highlight the strong influence of resonance between the proper frequency of the core and the spin of Mercury that raises the velocity field inside the core. We show that the key parameter is the polar flattening of the core. This effect cannot be directly derived from observations of the surface of Mercury, but we cannot exclude the possibility of an indirect detection by measuring the magnetic field.

Keywords: planets and satellites: individual: Mercury; planets and satellites: interior

Journal Article.  7110 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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