HR: 14:55h
AN: P53E-02 INVITED [Abstracts]
TI: Thermal Studies of Saturn's Rings
AU: * Pilorz, S
EM: stuart.pilorz@jpl.nasa.gov
AF: JPL, 4800 Oak Grove Dr., Pasadena, CA 91109, United States
AU: Altobelli, N
EM: naltobel@jpl.nasa.gov
AF: ESA/ESAC, Camino bajo del Castillo, s/n
Urbanizacio Villafranca del Castillo
Villanueva de la Canada, Madrid, 28692, Spain
AU: Leyrat, C
EM: cleyrat@jpl.nasa.gov
AF: JPL, 4800 Oak Grove Dr., Pasadena, CA 91109, United States
AU: Spilker, L
EM: linda.spilker@jpl.nasa.gov
AF: JPL, 4800 Oak Grove Dr., Pasadena, CA 91109, United States
AB:
The observed thermal emission from Saturn's rings has a locational and directional variation that ultimately
results from the time dependent response of individual ring particles to the quasi-periodic radiation forcing they
experience as they orbit Saturn. The observed thermal emission from any radial region of the rings is
representative of a large ensemble of particles or structures which are subject to statistically similar conditions
as they orbit. Near any particular radius, the thermal forcing and response are quasi-periodic around an orbit,
varying secularly with Saturn's twenty-nine year seasonal cycle.
This talk will discuss the coupled thermal and radiative transfer processes within the rings as determined by the
interplay between individual particle properties and those of the ensemble (i.e., the ring structure), and the
constraints that are placed on those by the most comprehensive thermal observations of the rings to date, taken
with the Cassini Infrared Spectrometer (CIRS). Over one hundred thousand thermal-infrared spectra of the rings,
between 10 and 500 cm-1, have been taken with the CIRS Focal Plane 1 (FP1) detector since Cassini orbit
insertion in July, 2004. They resemble scaled Planck functions with well resolved peaks indicative of
temperatures between approximately 60 and 120 K.
We investigate the properties of a mapping from a space of physical parameters describing ring particles and
their distribution onto predicted time-dependent spectral thermal emission. Ring emission is modeled using a
radiative transfer code augmented with ray tracing calculations; a thermal model is embedded within the
calculation to model the particles as a thermal source, and statistical averaging is incorporated. The model is
specified by a vector of parameters describing a vertically varying particle size distribution, spin distribution,
thermal inertia, albedo and optical depth, and when driven by radiation calculated from ephemeris parameters it
produces a self-consistent, time- and direction-dependent emission spectrum accounting for mutual shading,
interparticle heating, and directionally varying emission.
Any parameter vector generates a set of emission spectra that vary with orbital location and direction, and
perturbations of the parameters allow investigation of the mapping represented by the model.
We present analyses of the dimensionality of some sets of Cassini observations, evaluate the agreement of
some simple mono- and multi-layer toy models with these, and present sensitivity studies highlighting the
interplay of parameters and limitations of the model.
This research was carried out at JPL/Caltech, under contract with NASA.
DE: 0545 Modeling (4255)
DE: 5465 Rings and dust
DE: 6275 Saturn
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting