Ring Orbits from Multiple Occultation Observations

Details Ring Orbits from Multiple Occultation Observations Ring Orbits from Multiple Occultation Observations

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.4202f&link_type=abstract

American Astronomical Society, DPS meeting #38, #42.02; Bulletin of the American Astronomical Society, Vol. 38, p.559

Astronomy and Astrophysics

Astronomy

1

Scientific paper

Planetary rings provide a remarkable laboratory for the investigation of a wide range of dynamical effects, including resonance-driven density and bending waves, satellite wakes, shepherding of narrow ringlets, and non-circular edges of gaps. Careful quantitative examination of these features requires a very accurate absolute radius scale and planetary pole direction, achievable by combining multiple stellar and radio occultation observations. Uncertainty in the location of the spacecraft (at the km level) introduces a fundamental uncertainty into the geometric solution for the ring radius scale, and in the end one must solve for corrections to the spacecraft trajectory as part of the overall determination of the ring orbital model. Using JPL's NAIF toolkit, we have developed accurate algorithms for computing the event time of a ring occultation during an Earth-based or spacecraft occultation, including the effects of spacecraft trajectory errors mapped in two orthogonal directions transverse to the line of sight, based on osculating orbital elements for the instantaneous spacecraft path. These are the fundamental building blocks for a global solution for the pole direction and orbits of the rings of Saturn and Uranus. For Uranus, our new orbit solution includes the full set of digitally recorded occultation data from 1977-2002, yielding a radius scale accurate at the 100 meter level. For Saturn, we explore the potential for highly accurate ring orbit determination as occultation observations from dozens of stellar and radio occultations become publicly available over the course of the ongoing Cassini orbital tour. Saturn's pole precession is also detectable from ring occultation data, and we set limits on the accuracy of the precession rate determination and the implications for our understanding of the mass distribution in Saturn's interior. This work was supported in part by the NASA PGG program.

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