A Multilayer Model For Thermal Infrared Emission Of Saturn'S Rings: Particle Properties Estimated From Cassini-CIRS Data In The Early Phase

Details A Multilayer Model For Thermal Infrared Emission Of Saturn'S Rings: Particle Properties Estimated From Cassini-CIRS Data In The Early Phase A Multilayer Model For Thermal Infrared Emission Of Saturn'S Rings: Particle Properties Estimated From Cassini-CIRS Data In The Early Phase

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.1804m&link_type=abstract

American Astronomical Society, DPS meeting #41, #18.04

Astronomy and Astrophysics

Astronomy

Scientific paper

Since the Saturn orbit insertion of the Cassini spacecraft in mid-2004, the Cassini composite infrared spectrometer (CIRS) measured temperatures of Saturn's main rings at various observational geometries. In the present study, we apply our new thermal model for fitting to Cassini-CIRS data in the early phase. Our model is based on classical radiative transfer and takes into account the heat transport due to particle motion in the azimuthal and vertical directions. We assume a bimodal size distribution consisting of particles with spherically symmetric temperatures and non-spinning Lambert particles, which we call fast and slow rotators, respectively. The most important parameters, which control ring temperatures, are the albedo in visible light A, the fraction of fast rotators in cross section f, and the thermal inertia Γ. From the data fitting, we obtain [A,f,Γ] = [0.17(+0.06 -0.10),0.67(+0.07 -0.08),20(+32 -20)], [0.67(+0.03 -0.09),0.10(+0.20 -0.10),14(+32 -13)], [0.55(+0.03 -0.03),0.48(+0.24 -0.19), 11(+8 -7)], and [0.52(+0.02 -0.01),0.76(+0.15 -0.17),18(+7 -5)] for the C, B, inner A, and outer A rings, respectively. Here Γ is in MKS units, and we take into account the uncertainty of vertical motion of particles for the B ring, namely, whether particles rebound at the mid plane due to mutual collisions or not. The albedo values are consistent with those obtained in photometric observations, except our model indicates a smaller albedo for the C ring; this is probably because the emissivity of particles in the C ring is slightly lower than unity.
This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Government sponsorship acknowledged.

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