Deviation of Mercury's spin axis from an exact Cassini state induced by dissipation

Abstract

Viscous and electromagnetic drag at the fluid core boundaries generate a deviation that does not exceed 0.1 arcsec• In units of arcsec, the phase lag from tidal dissipation follows the empirical relation (80/Q),where Q is the quality factor• The maximum phase lag allowed by observations gives a lower limit on the bulk mantle viscosity of approximately 10 17 Pa s