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P. A. Yanamandra-Fisher, B. M. Fisher, G. S. Orton, M. Ressler (JPL/CIT), B. Beach-Kimball (Univ. Conn.), I. Suarez (PCC), V. U (CIT)
We initiated an observational campaign of near- and mid-infrared spectrophotometry of Saturn's main rings from the 1995 Earth -- Saturn ring plane crossings epoch. We acquired data at the NASA/InfraRed Telescope Facility (IRTF) from 1995 to 2002 with NSFCAM, a 1-5 \mum camera, and MIRLIN, a 10-\mum camera, at several diagnostic wavelengths spanning the spectral interval from 1.58- to 24-\mum. Our observational program has, therefore, covered nearly one third of a Saturnian year, following the progressive march of the rings from their edge-on presentation at the equator in 1995 (vernal equinox) to their maximum opening, obscuring the northern pole of Saturn (southern summer solstice). Our specific scientific objectives are to determine near-infrared reflectivity, brightness temperature, thermal inertia, opacities of the rings and azimuthal/ansae asymmetries. Our preliminary results indicate that the brightness temperature of the rings peaks near 18 \mum, with a east/west ansae asymmetry of few degrees, similar to the near-infrared reflectivity asymmetry. Our current efforts are aimed at modelling Ring A near-infrared reflectivity and thermal properties as function of solar elevation (or ring opening angle ROA from 0 to 26\circ), inclination and phase angle to gain insight into the nature of the ring particles. Over the range of ROA, particles in Ring A experienced thermal heating and cooling as they entered and exited Saturn shadow. In 2003-04, Ring A was outside the planetary shadow, not experiencing any thermal cooling nor heating, thereby allowing the decoupling of planetary shadow effects and azimuthal heterogeneities.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.