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Probing Saturn’s tropospheric cloud with Cassini/VIMS

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journal contribution
posted on 02.03.2016, 09:46 by J. K. Barstow, P. G. J. Irwin, Leigh Nicholas Fletcher, R. S. Giles, C. Merlet
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.

History

Citation

Icarus, 2016, 271, pp. 400–417

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

AM (Accepted Manuscript)

Published in

Icarus

Publisher

Elsevier for Academic Press Inc.

issn

0019-1035

Acceptance date

07/01/2016

Copyright date

2016

Available date

19/01/2018

Publisher version

http://www.sciencedirect.com/science/article/pii/S0019103516000178

Notes

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.

Language

en

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