North vs South on Saturn: Discovery of a Pronounced Hemispherical Asymmetry in Saturn's 5-Micron Emission and Associated Deep Cloud Structure by Cassini/VIMS

Details North vs South on Saturn: Discovery of a Pronounced Hemispherical Asymmetry in Saturn's 5-Micron Emission and Associated Deep Cloud Structure by Cassini/VIMS North vs South on Saturn: Discovery of a Pronounced Hemispherical Asymmetry in Saturn's 5-Micron Emission and Associated Deep Cloud Structure by Cassini/VIMS

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.0503b&link_type=abstract

American Astronomical Society, DPS meeting #38, #05.03; Bulletin of the American Astronomical Society, Vol. 38, p.488

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We report the discovery of a pronounced North/South hemispherical asymmetry in the 5-micron radiation emitted from Saturn's interior observed by Cassini/VIMS in global-scale spectral images of the planet's nightside. These nightside images, uncontaminated by sunlight which otherwise adds significant reflected light to the southern summer hemisphere, shows that northern latitudes poleward of 8 degrees latitude emit about twice the 5-micron flux as their southern latitude counterparts. Such asymmetry has now been seen consistently in 2005 and 2006, whenever VIMS has been able to image both the north and south nightside hemispheres. The 2:1 difference in hemispherical emission is nearly uniform over the entire 5-micron emission spectrum from 4.8 to 5.1 microns, spanning 21 VIMS channels. As noted previously (Baines et al., Earth, Moon, and Planets 96, 119-147), such 2:1 5-micron flux variations are regularly seen in high-spatial resolution imagery on Saturn, indicating significant small-scale variability in cloud cover near the 2-bar level (Baines et al., BAAS 37, 658). Similarly, the 2:1 hemispherical variability likely indicates a global-scale variation in the opacity of Saturn's deep clouds, with northern clouds having an average 5-micron optical depth about 0.7 less than the average southern cloud. This hemispherical difference may be a manifestation of seasonal changes at depth on Saturn, with distinct thinning of deep-seated (likely ammonium hydrosulfide and/or water) clouds in the winter northern hemisphere and/or thickening of these deep clouds in the summer southern hemisphere. Such possible seasonal variability in Saturn's deep-cloud structure will be monitored over the next few years as Saturn encounters equinox conditions in 2010.

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