Mercury's resonant rotation from secular orbital elements

Abstract

We used recently produced Solar System ephemerides, which incorporate two years of ranging observations to the MESSENGER spacecraft, to extract the secular orbital elements for Mercury and associated uncertainties. As Mercury is in a stable 3:2 spin-orbit resonance these values constitute an important reference for the planet's measured rotational parameters, which in turn strongly bear on physical interpretation of Mercury's interior structure. In particular, we derive a mean orbital period of 87.96934962 $\pm$ 0.00000037 days and (assuming a perfect resonance) a spin rate of 6.138506839 $\pm$ 0.000000028 degree/day. The difference between this rotation rate and the currently adopted rotation rate (Archinal et al, 2011) corresponds to a longitudinal displacement of approx. 67 m per year at the equator. Moreover, we present a basic approach for the calculation of the orientation of the instantaneous Laplace and Cassini planes of Mercury. The analysis allows us to assess the uncertainties in physical parameters of the planet when derived from observations of Mercury's rotation.

References in corpus (4)

• The free precession and libration of Mercury
• INPOP new release: INPOP10e
• Effect of core--mantle and tidal torques on Mercury's spin axis orientation
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• The influence of a fluid core and a solid inner core on the Cassini sate of Mercury
• The reference frames of Mercury after MESSENGER
• A Post-Newtonian Analysis of Regularized 4D-EGB Theory: Complete Set of PPN Parameters and Observational Constraints
• Deviation of Mercury's spin axis from an exact Cassini state induced by dissipation