A Mercury orientation model including non-zero obliquity and librations |
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| Authors: | Jean-Luc Margot |
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| Institution: | (1) University of Virginia, Charlottesville, VA, USA;(2) U.S. Geological Survey, Flagstaff, AZ, USA;(3) University of Maryland, College Park, MD, USA;(4) W. M. Keck Observatory, Kamuela, HI, USA;(5) Vatican Observatory, Vatican City State, Italy;(6) IMCCE, Paris Observatory, CNRS, Paris, France;(7) U.S. Naval Observatory, Washington DC, USA;(8) Institute for Applied Astronomy, St. Petersburg, Russia;(9) NASA Goddard Space Flight Center, Greenbelt, MD, USA;(10) DLR Berlin Adlershof, Berlin, Germany;(11) University of Western Ontario, London, Canada;(12) University of New Hampshire, Durham, NH, USA;(13) University of Hawaii, Honolulu, HI, USA;(14) Cornell University, Ithaca, NY, USA;(15) Queen Mary, University of London, London, UK |
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| Abstract: | Planetary orientation models describe the orientation of the spin axis and prime meridian of planets in inertial space as
a function of time. The models are required for the planning and execution of Earth-based or space-based observational work,
e.g. to compute viewing geometries and to tie observations to planetary coordinate systems. The current orientation model
for Mercury is inadequate because it uses an obsolete spin orientation, neglects oscillations in the spin rate called longitude
librations, and relies on a prime meridian that no longer reflects its intended dynamical significance. These effects result
in positional errors on the surface of ~1.5 km in latitude and up to several km in longitude, about two orders of magnitude
larger than the finest image resolution currently attainable. Here we present an updated orientation model which incorporates
modern values of the spin orientation, includes a formulation for longitude librations, and restores the dynamical significance
to the prime meridian. We also use modern values of the orbit normal, spin axis orientation, and precession rates to quantify
an important relationship between the obliquity and moment of inertia differences. |
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