Effects of Janus' orbit change every four years on Saturn's A ring
Abstract
Every four years, Janus and Epimetheus change their orbits, because of their unique dynamical capture in horseshoe orbits (Yoder et al, 1983). Both Janus and Epimetheus drive strong density waves in the rings, but because of their configuration with variable orbits, their nearby resonance locations change every four years. As a result, the observed composite waves are driven by both satellites, each at two different semimajor axes at different times (Tiscareno et al, 2007). Moreover, the 7:6 Lindblad resonance with Janus controls the edge of the A ring, which is also affected by this dynamical behavior. We have examined a series of mosaics of the A ring edge derived from Cassini ISS images taken between 2005 and 2014, as well as large suite of occultation data. During the first period (2006 to 2009), when Janus was on its inner orbital leg, we have a regular 7-lobed pattern, with one minimum aligned with the orbital longitude of Janus, in agreement with the results obtained by Spitale and Porco (2009). Fits to the occultation data show a strong m=7 radial perturbation with an amplitude of 12.8 km, moving with Janus. During the second period (2010 to 2013), when Janus was on its outer orbital leg, we see a more irregular pattern with typically 5 or 6 lobes. We also see no obvious alignment with Janus. Individual distinctive features on the A edge appear to move at the keplerien rate over periods of several days. We will present a more complete analysis of these data and suggest a possible dynamical model for the behavior of the A ring edge after 2010.
- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #46
- Pub Date:
- November 2014
- Bibcode:
- 2014DPS....4640204E