Towards an Understanding of Thermal Throughput across Saturn's Rings with Cassini CIRS

One of the more striking aspects of Saturn's main ring system is its aspect ratio. It spans over 270,000 km from ansa to ansa, yet its thickness normal to the ring plane is less than a million times its breadth. Hence, studies of the rings’ structure focus mostly on radial and azimuthal features. But in the thermal infrared the finite vertical thickness of the main rings is clearly manifest in the measured temperature differences between that face of the rings exposed to direct solar illumination (the lit face) and the opposite (unlit) face derived from observations with Cassini's Composite Infrared Spectrometer (CIRS).

As previous work has shown (Spilker et al., 2006), the thermal flux from Saturn’s rings observed by CIRS is a function of observing geometry. To control for these variations, we specifically designed paired observations of the lit and unlit sides of the rings where observing variables such as the emission, phase and local hour angles were kept as similar as possible to facilitate direct comparison between the lit and unlit observations. The ultimate goal of this work is to understand these lit/unlit temperature differentials and their variation with radius and optical depth. Constraining the amount of thermal energy exchange between the lit and unlit sides of the rings will allow us to derive information about the main rings' structure and dynamics in this third dimension. This presentation is a progress report on our analysis of such observations and our plans for future work.

This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Copyright 2014 California Institute of Technology. Government sponsorship acknowledged.