A Post-Equinox View of Saturn’s rings
LW Esposito
University of Colorado
Boulder CO 30309-0392
Cassini observed the Saturn Equinox of 2009, providing a unique geometry and
unexpected findings:
1. The oblique lighting exposed vertical ring structure and embedded objects;
2. Saturn’s Rings were the coldest ever;
3. Cassini images inspired new occultation and spectral analysis of ring structures
like those in the images.
Steady progress and new discoveries continue after the equinox. We can now
recognize some aspects of a ‘Post-Equinox View’:
1. Cassini equinox observations show Saturn’s rings as a complex geophysical
system, incompletely modeled as a single-phase fluid;
2. Self-gravity causes wakes, viscosity, overstabilty and local aggregate growth
3. Larger fragments may provide the seeds for growth of new aggregates;
4. The F ring may be the easiest place to observe aggregation/disaggregation.
These findings have significant implications for our understanding of ring dynamics,
origin and history:
1. Self-gravity plays a large role;
2. Accretion continues today in rings A, B, C and F, that can renew the ring material;
3. Resonance forcing and Kepler shear provide the energy for a multitude of
dynamics and local aggregate growth;
4. Structure forms throughout the rings, at scales from meters to kilometers
Questions that we now can address following the equinox:
1. Is the red color of the rings caused by Carbon or nano-hematite?
2. Are the rings young or old?
3. Can we estimate the B ring mass from haloes, or from precession of CD ringlets?
4. Or must we wait until the ring gravity is evident during Cassini’s final orbits?
5. What is the relative contribution of deterministic and stochastic forcing in
creating the observed structure?
6. Do moons continue to form today?
I will review these new findings, questions and possible paths to answers. Those
who attend my poster will be asked for their own views.