HR: 1340h
AN: P43B-1295    [Abstracts]
TI: Infrared Observations Of Saturn's Rings : Azimuthal Variations And Thermal Modeling
AU: * Leyrat, C
EM: cedric.leyrat@jpl.nasa.gov
AF: Jet Propulsion Laboratory - California Institute of Technology, 4800 Oak Grove Drive, PASADENA, CA 91109, United States
AU: Spilker, L J
EM: Linda.J.Spilker@jpl.nasa.gov
AF: Jet Propulsion Laboratory - California Institute of Technology, 4800 Oak Grove Drive, PASADENA, CA 91109, United States
AU: Altobelli, N
EM: nicolas.altobelli@sciops.esa.int
AF: European Space Agency ESA/ESAC, European Space Astronomy Centre (ESAC) P.O. Box - Apdo. de correos 50727, MADRID, 28080, Spain
AU: Pilorz, S
EM: stuart.pilorz@jpl.nasa.gov
AF: Jet Propulsion Laboratory - California Institute of Technology, 4800 Oak Grove Drive, PASADENA, CA 91109, United States
AU: Ferrari, C
EM: cecile.ferrari@discovery.saclay.cea.fr
AF: University Paris 7 / CEA Saclay, SAp/CEA Saclay Orme des merisiers, Bat 709, Gif sur Yvette, 91191, France
AU: Edgington, S G
EM: Scott.G.Edgington@jpl.nasa.gov
AF: Jet Propulsion Laboratory - California Institute of Technology, 4800 Oak Grove Drive, PASADENA, CA 91109, United States
AU: Wallis, B D
EM: bwallis@frazmtn.com
AF: Jet Propulsion Laboratory - California Institute of Technology, 4800 Oak Grove Drive, PASADENA, CA 91109, United States
AU: Nugent, C
EM: cnugent@ucla.edu
AF: UCLA University of California, Department of Earth and Space Sciences 595 Charles Young Drive East, LOS ANGELES, CA 90095, United States
AU: Flasar, M
EM: Michael.Flasar@gsfc.nasa.gov
AF: Goddard Spaceflight Center, Planetary Systems Branch, Code 693, GREENBELT, MD 20771, United States
AB: Saturn's rings represent a collection of icy centimeter to meter size particles with their local dynamic dictated by self gravity, mutual collisions, surface roughness and thickness of the rings themselves. The infrared observations obtained by the CIRS infrared spectrometer on board Cassini over the last 3.5 year contain informations on the local dynamic, as the thermal signature of planetary rings is influenced both by the ring structure and the particle properties. The ring temperature is very dependent on the solar phase angle (Spilker et al., this issue), and on the local hour angle around Saturn, depending on whether or not particles' visible hemispheres are heated by the Sun. The geometric filling factor, which can be estimated from CIRS spectra, is less dependent on the local hour angle, suggesting that the non isothermal behavior of particles' surfaces have low impact, but it is very dependent on the spacecraft elevation for the A and C rings. The ring small scale structure can be explored using CIRS data. Variations of the filling factor with the local hour angle relative to the spacecraft azimuth reveals self-gravity wakes. We derive morphological parameters of such wakes in both A and B rings assuming that wakes can be modeled either by regularly spaced bars with infinite or finite optical depth. Our results indicates that wakes in the A ring are almost flat, with a ratio height/width ≈ 0.44 ± 0.16 and with a pitch angle relative to the orbital motion direction of ≈ 27deg. This is consistent with UVIS (Colwell et al., 2006) and VIMS data (Hedman et al., 2007). Such models are more difficult to constrain in the B ring, but small variations of the filling factor indicate that the pitch angle decreases drastically in this ring. We also present a new thermal bar model to explain azimuthal variations of temperatures in the A ring. We compare results with previous ring thermal models of spherical particles. The Cassini/CIRS azimuthal scans data set is crucial input for any future modeling of Saturn's rings' thermal and dynamical properties.
DE: 6265 Planetary rings
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting