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Title: Probing Saturn’s tropospheric cloud with Cassini/VIMS
Authors: Barstow, J. K.
Irwin, P. G. J.
Fletcher, Leigh Nicholas
Giles, R. S.
Merlet, C.
First Published: 19-Jan-2016
Publisher: Elsevier for Academic Press Inc.
Citation: Icarus, 2016, 271, pp. 400–417
Abstract: In its decade of operation the Cassini mission has allowed us to look deep into Saturn’s atmosphere and investigate the processes occurring below its enshrouding haze. We use Visual and Infrared Mapping Spectrometer (VIMS) 4.6–5.2 µ m data from early in the mission to investigate the location and properties of Saturn’s cloud structure between 0.6 and 5 bar. We average nightside spectra from 2006 over latitude circles and model the spectral limb darkening using the NEMESIS radiative transfer and retrieval tool. We present our best-fit deep cloud model for latitudes −40∘<λ<50∘,−40∘<λ<50∘, along with retrieved abundances for NH3, PH3 and AsH3. We find an increase in NH3 abundance at the equator, a cloud base at ∼2.3 bar and no evidence for cloud particles with strong absorption features in the 4.6–5.2 µm wavelength range, all of which are consistent with previous work. Non-scattering cloud models assuming a composition of either NH3 or NH4SH, with a scattering haze overlying, fit limb darkening curves and spectra at all latitudes well; the retrieved optical depth for the tropospheric haze is decreased in the northern (winter) hemisphere, implying that the haze has a photochemical origin. Our ability to test this hypothesis by examining spectra at different seasons is restricted by the varying geometry of VIMS observations over the life of the mission, and the appearance of the Saturn storm towards the end of 2010.
DOI Link: 10.1016/j.icarus.2016.01.013
ISSN: 0019-1035
Version: Post-print
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2016 Published by Elsevier Inc. This manuscript version is made available after the end of the embargo period under the CC-BY-NC-ND 4.0 license 
Description: The file associated with this record is under a 24-month embargo from publication in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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