Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.6704y&link_type=abstract
American Astronomical Society, DPS meeting #41, #67.04
Astronomy and Astrophysics
Astronomy
Scientific paper
The shaking of Mercury's orbit by the planets forces librations in longitude in addition to those at harmonics of the orbit period that have been used to detect Mercury's molten core.
We extend the analytical formulation of Peale et al (2009) in order to predict the amplitude and the phase of these long period forced librations.
The perturbation by Jupiter could have an amplitude exceeding the 35 arcsec amplitude of the 88 day forced libration because the 11.86 year period of forcing is near the 12 year free libration period.
We develop an equation linking the long period libration amplitudes and the moment of inertia ratio (B-A)/Cm. The libration amplitude is proportional to this ratio far enough from the resonance.
The model for the time evolution of the rotation angle and rotation rate is very close to the solution obtained through a numerical integration of the equations of motion.
The amplitude of the librations in longitude caused by the planetary perturbations of the orbit affect the spin rate at a level that may be too small to be detectable in the radar data. However, because of the accumulation of long period phase, they affect the angular orientation of Mercury about its rotation axis at a possibly detectable level.
This will need to be taken into account to interpret future spacecraft observations that rely on angular measurements (imaging, gravity) instead of spin rate measurements.
Margot Jean-Luc
Peale Stanton J.
Yseboodt Marie
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