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N. Altobelli, L. Spilker, S. Pilorz, S. G. Edgington, B. Wallis (NASA-JPL), F.M. Flasar (Goddart Space Flight Center)
We analyze data sets obtained with the Composite Infrared Spectrometer (CIRS) on-board the Cassini spacecraft after the Saturn Orbit Insertion (SOI). Our goal is to benefit from the high spatial resolution and the various viewing geometries offered by the mid-IR interferometer (FP3 channel, 600 cm-1-1100 cm-1) to derive detailed radial temperature profiles for both the C ring and the Cassini Division.
Thermal radial profiles were derived previously for the C ring from the Voyager IRIS data, suggesting a decrease in temperature with increasing Saturn distance. Models of the Voyager data reproduced this trend, taking into account the incident Saturn thermal flux, but uncertainties remained on local variations in particle albedo or particle density. In particular, the IRIS data seem to underestimate the optically thicker ringlets. Using the CIRS FP3 1x10 array of detectors allows better resolution of the local temperature variations and therefore the ability to sense finer structures of the C ring. Scans over the Cassini Division performed with FP1 during SOI also revealed structures at the limit of the detector's resolution. As the spacecraft will never be so close again to the ring, we use FP3 scans to resolve the cooler and optically thicker ringlets in this region.
While high resolution scans (long exposure time) improve the temperature fit, they lead to a smear of the footprints (because of the spacecraft motion) which should be minimized to resolve fine-scale radial structures. We also check the consistency of our temperature fits using the high resolution values for the optical thickness as provided by the Voyager photopolarimeter subsystem. This allows us to better constrain the FP3 geometrical filling factor, which improves the quality of the temperature fits. Our preliminary results will be presented.
This work was performed at NASA-JPL under NRC grant.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.