HR: 1340h
AN: P43B-1297    [Abstracts]
TI: The Vertical Temperature Distribution Across Saturn's Rings as Observed by Cassini CIRS
AU: * Brooks, S M
EM: Shawn.M.Brooks@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive M/S 230-205, Pasadena, CA 91109,
AU: Spilker, L J
EM: Linda.J.Spilker@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive M/S 230-205, Pasadena, CA 91109,
AU: Pilorz, S H
EM: Stuart.H.Pilorz@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive M/S 230-205, Pasadena, CA 91109,
AU: Edgington, S G
EM: Scott.G.Edgington@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive M/S 230-205, Pasadena, CA 91109,
AU: Cuzzi, J N
EM: cuzzi@cosmic.arc.nasa.go
AF: NASA Ames Research Center, M/S 245-3, Moffett Field, CA 94035,
AB: 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 may be responsible for modifying the overall thermal budget. 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 (e.g.\ Froidevaux 1981, Ferrari and Leyrat 2006) or a multilayer (e.g.\ Kawata, 1983). 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.\ similar phase angle, local hour angle and solar elevation angle). The Sun was at elevation angles, B' , between 20.5° and 23.5° when these observations were made. Practically no discernible temperature difference is observed between the lit and unlit sides of the optically thin C ring. This is expected, as the radiation field should be 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 temperature differences of 18 - 20 K at high phase angles ( 125 - 150° ). At low phase angles ( < 60° ), the observed difference in temperature across the core of the B ring is 25 K . We will present a simple, empricial model to construct a framework within which to interpret these observations. However, a full understanding of the model results await more observations and a more complex model that takes the behavior of Saturn's ring particles more fully into account.
DE: 5759 Rings and dust
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting