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Cassini thermal observations of Saturn's main rings: Implications for particle rotation and vertical mixing

Spilker, Linda J. and Pilorz, Stuart H. and Wallis, Brad D. and Pearl, John C. and Cuzzi, Jeffrey N. and Brooks, Shawn M. and Altobelli, Nicolas and Edgington, Scott G. and Showalter, Mark and Flasar, F. Michale and Ferrari, Cecile and Leyrat, Cedric (2006) Cassini thermal observations of Saturn's main rings: Implications for particle rotation and vertical mixing. Planetary and Space Science, 54 (12). pp. 1167-1176. ISSN 0032-0633. doi:10.1016/j.pss.2006.05.033.

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In late 2004 and 2005 the Cassini composite infrared spectrometer (CIRS) obtained spatially resolved thermal infrared radial scans of Saturn's main rings (A, B and C, and Cassini Division) that show ring temperatures decreasing with increasing solar phase angle, α, on both the lit and unlit faces of the ring plane. These temperature differences suggest that Saturn's main rings include a population of ring particles that spin slowly, with a spin period greater than 3.6 h, given their low thermal inertia. The A ring shows the smallest temperature variation with α, and this variation decreases with distance from the planet. This suggests an increasing number of smaller, and/or more rapidly rotating ring particles with more uniform temperatures, resulting perhaps from stirring by the density waves in the outer A ring and/or self-gravity wakes. The temperatures of the A and B rings are correlated with their optical depth, τ, when viewed from the lit face, and anti-correlated when viewed from the unlit face. On the unlit face of the B ring, not only do the lowest temperatures correlate with the largest τ, these temperatures are also the same at both low and high α, suggesting that little sunlight is penetrating these regions. The temperature differential from the lit to the unlit side of the rings is a strong, nearly linear, function of optical depth. This is consistent with the expectation that little sunlight penetrates to the dark side of the densest rings, but also suggests that little vertical mixing of ring particles is taking place in the A and B rings.

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Additional Information:© 2006 Elsevier Ltd. Accepted 4 May 2006; available online 26 July 2006. The authors gratefully acknowledge Paul Romani, Richard Achterberg and Conor Nixon for their help designing and planning the CIRS ring observations. Thanks also to Thomas Spilker for helpful technical discussions and comments on the manuscript. We also acknowledge support from Judicael Decriem. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
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Subject Keywords:Saturn’s rings; Cassini; Cassini composite infrared spectrometer; Thermal ring measurements
Issue or Number:12
Record Number:CaltechAUTHORS:20110809-115150921
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Official Citation:Linda J. Spilker, Stuart H. Pilorz, Brad D. Wallis, John C. Pearl, Jeffrey N. Cuzzi, Shawn M. Brooks, Nicolas Altobelli, Scott G. Edgington, Mark Showalter, F. Michael Flasar, Cecile Ferrari, Cedric Leyrat, Cassini thermal observations of Saturn's main rings: Implications for particle rotation and vertical mixing, Planetary and Space Science, Volume 54, Issue 12, Surfaces and Atmospheres of the Outer Planets, their Satellites and Ring Systems from Cassini-Huygens Data, October 2006, Pages 1167-1176, ISSN 0032-0633, DOI: 10.1016/j.pss.2006.05.033.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24766
Deposited On:09 Aug 2011 21:16
Last Modified:09 Nov 2021 16:26

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