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T.A. Livengood (U of MD \& NASA/GSFC), T. Kostiuk (NASA/GSFC), C.M. Lisse (STScI), H.U. K\"aufl (ESO Garching)
The Saturn system was imaged at mid-infrared wavelengths in October-December 1996 using the Thermal Infrared MultiMode Instrument (TIMMI) on the 3.6m telescope of the European Southern Observatory. The sub-earth point was about -3.3\circ latitude (planetocentric) at this time, presenting a low inclination angle view of the rings. Photometric images were made in six filters from 7.6~\mum to 12.8~\mum with the TIMMI 64\times 64 Ga:Si array at an image scale of 0.47~arcsec/pixel. The image radiance has been absolutely calibrated with disc-center signal from Jupiter images acquired at times and airmass similar to the Saturn images, compared with Voyager IRIS spectroscopy of the same region on Jupiter. Preliminary analysis of the ring photometry indicates a peak in the emitted radiance of the rings near 12~\mum. A significant difference in the radiance from the East and West ansae is observed, with the West (receding) ansa brighter than the East (approaching) ansa. The W/E brightness ratio is wavelength-dependent, with a maximum near 12~\mum. Spatial resolution in the images is sufficient to examine radial dependence in the ring signal and in the W/E brightness asymmetry with discrimination of ~1/20 Saturn radius. Possible explanations for the brightness asymmetry will be discussed, including thermal heating and cooling, ring geometry, and ring particle properties and composition.
The authors acknowledge the support of the NASA Planetary Astronomy Program and of the NSF Planetary Astronomy Program.
The author(s) of this abstract have provided an email address for comments about the abstract: timothy.a.livengood@gsfc.nasa.gov