Uranian ring orbits
Abstract
Most of our detailed knowledge of the dynamics, detailed structure, and orbital characteristics of the narrow Uranian rings has come from more than 25 years of Earth-based and spacecraft occultations. First detected on March 10, 1977, during a campaign to study the atmosphere of Uranus from a stellar occultation of SAO158687 (Elliot et al. 1977, Nature 267,328; Millis et al. 1977, Nature 267,330; Hubbard et al. 1980, Astron J. 845,1663), dozens of high-SNR occultations were observed as Uranus traversed the star-rich field of the Milky Way, but observations had dwindled by 2002 because Uranus had moved to a region with fewer background stars, high-speed InSb aperture photometers were being phased out at major observatories, eliminating the capability of ~100 Hz IR photometry in the 2.2 methane band, and the rings were approaching an edge-on view from the Earth, reducing the transit time of the star across the projection of each ring and thus reducing the SNR still further. Thus, the 1977-2002 Uranus occultation data represent a complete and distinct set of ring measurements. As part of a ring data archiving project supported by NASA's PDART program, we have assembled a comprehensive set of Uranus occultation data from this period and have determined an updated geometric model for the Uranus system, including a complete set of keplerian orbital elements for the ten classical narrow rings, a solution for the direction of the planet's pole, and fitted values for the planet's gravitational harmonic coefficients J2 and J4. Our results are consistent with those of Jacobson 2014 (Astron. J. 148/5/76), but in addition we identify and determine the amplitudes, pattern speeds, and phases of six normal modes for three rings: the m=2 mode for the delta ring, the m=3 mode for the eta ring (see Chancia et al. 2017, Astron. J. 154/4/153) , and the m=0, 6, -1, and -2 modes for the gamma ring (see French et al. this conference).
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.477F