Saturn Ring Temperatures at Equinox with Cassini CIRS

Details Saturn Ring Temperatures at Equinox with Cassini CIRS Saturn Ring Temperatures at Equinox with Cassini CIRS

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p51b1131s&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P51B-1131

Physics

[6265] Planetary Sciences: Solar System Objects / Planetary Rings, [6275] Planetary Sciences: Solar System Objects / Saturn

Scientific paper

The Cassini Composite infrared spectrometer (CIRS) retrieved the temperatures of Saturn’s main rings at equinox for the first time, as the sun traversed from the south to north side of the rings. At equinox the rings are edge-on as seen from the sun and essentially edge-on (maximum ring opening of only about 2.5 degrees) as seen from the Earth, so it is not possible to measure the main ring temperatures from Earth. The main rings cooled to their lowest temperatures measured to date. At equinox the solar input is very small and the primary heat sources for the rings are Saturn thermal and visible energy. Temperatures are almost identical for similar geometries on the north and south sides of the rings. The ring temperatures at equinox were: C ring, 55-75 K; B ring, 45-60 K; Cassini Division, 45 - 58 K; and A ring, 43 - 52 K. CIRS has acquired a wide-ranging set of thermal measurements of Saturn’s main rings (A, B, C and Cassini Division) at solar elevations from zero to 24 degrees. The equinox geometry is unique because Saturn heating dominates, contrasted to earlier in the mission when the primary heat source is visible-wavelength energy from the sun. When the sun is the dominant heat source the ring temperature varies between the lit and unlit sides of the A and B rings. As the solar elevation decreased the last few degrees, the ring temperatures on the lit and unlit sides of the rings decreased in a non-linear fashion. The thermal model by Morishima et al. (2009) is able to reproduce most of the equinox temperatures observed by CIRS. Equinox results will be presented. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Copyright 2009 California Institute of Technology. Government sponsorship acknowledged.

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