Examining Ring Particle Vertical Transport with Cassini CIRS
Abstract
Dynamical interactions such as mutual collisions between ring particles and resonances with Saturn's moons conspire to insure that the particles comprising Saturn's rings not only have non-zero eccentricities, but finite inclinations as well. As a result, ring particles can generally be expected to cross above and below the ring plane as they orbit Saturn. Thermal models published to date do not consider this vertical transport across the ring plane, but constrain them to lie in either a static monolayer (Froidevaux, 1981; Ferrari and Leyrat, 2006) or multilayer (Kawata, 1983).
We have analyzed observations from Cassini's Composite Infrared Spectrometer (CIRS) from 10 to 600 cm-1 to identify those regions where ring particle vertical motion modifies the overall thermal budget. We compare the thermal flux emitted from the lit side of the rings to that coming from the unilluminated side using pairs of CIRS radial scans with otherwise similar geometric parameters (i.e. phase angle, local hour angle and solar inclination angle). Practically no discernible flux difference is observed between the lit and unlit sides of the optically thin C ring. This is expected, as the radiation field is relatively constant across such a thin layer of particles. The optically thickest portions of the B ring, where large filling factors and high collision rates impede ring particles from crossing the ring plane, display flux differences of 1.6 - 1.8 W/m2 at high phase angles (125 - 150°). At low phase angles (< 60°), the observed difference in thermal flux across the core of the B ring is 2.5 W/m2. At regions of intermediate optical depth, τ 1, thermal flux differences measured by CIRS are lower than a simple slab model would predict. These are regions where vertical mixing is expected to be significant.- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #38
- Pub Date:
- September 2006
- Bibcode:
- 2006DPS....38.4707B