Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p13b1675s&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P13B-1675
Physics
[6265] Planetary Sciences: Solar System Objects / Planetary Rings, [6275] Planetary Sciences: Solar System Objects / Saturn
Scientific paper
For a few days around Saturn ring equinox, the Cassini Composite Infrared Spectrometer (CIRS) obtained data on Saturn's rings at different local times and phase angles. We examine results from 15 scans taken near equinox. The sun was shining on the south side of the rings prior to the equinox crossing. The solar elevation angle in the 15 scans varied between -0.00007 degrees and 0.036 degrees and the phase angle ranged from 30 degrees to 147 degrees. The equinox geometry is unique because the sun is edge-on to the rings. Saturn heating dominates while solar heating is at a minimum. The ring temperature varies between the lit and unlit sides of the A and B rings when the sun is the dominant heat source. With the sun shining on the rings the temperature of the lit rings decreases with increasing phase angle and the ring temperature in the shadow is less than the ring temperature at noon. At equinox the ring temperature does not decrease with increasing phase angle and the temperature at noon is no longer greater than the temperature in the shadow. As the solar elevation angle decreased the last few degrees, the ring temperatures on the lit and unlit sides rapidly decreased to the coldest temperatures observed thus far. At equinox radial and longitudinal temperature variations are observed in the A, B and C rings and the Cassini Division. The radial temperature variations result both from the decreasing Saturn solid angle with increasing distance from the planet and varying optical depth as the screening effect of optically thicker rings limits the heat contribution to primarily one hemisphere of Saturn. Both monolayer and multilayer models can explain the radial variations in ring temperature except for the A ring. A ring model fits produce temperatures that are lower than observed temperatures perhaps because of the effects from gravitational wakes, density waves and bending waves that are not included in the models. Saturn ring temperatures near equinox also vary with ring local time, especially in the C ring which is the closest to the Saturn heating source. Model results will be discussed. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA and at CEA Saclay supported by the "Centre National d'Etudes Spatiales". Copyright 2011 California Institute of Technology. Government sponsorship acknowledged.
Ferrari Cecile
Morishima Ryuji
Spilker Linda J.
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