Lowell Observatory Colloquia

The Depths of Saturn: New Insights into the Dynamics and Chemistry of Saturnís Tropospheric Meteorology revealed by Cassini/VIMS and RADAR Imagery and Spectra

Kevin Baines, Jet Propulsion Laboratory

Lowell Observatory, Giclas Lecture Hall, December 13, 2012 at 3:30 p.m.

Numerous meteorological features in the depths of Saturn down to the ~ 4-bar level have been discovered and characterized by the Visual Infrared Mapping Spectrometer (VIMS) onboard the Cassini Orbiter. Salient among these features are: (1) a long-lived (> 5 year) "String of Pearls" chain of 20-24 regularly-spaced, similarly-sized circular cloud-clearings near the 3-bar-level at temperate latitudes, (2) numerous equatorial plumes in the 2-3-bar level centered near 6o latitude in both the northern and southern hemispheres, and (3) two types of convective storm- generated clouds observed erupting up to the 300 mbar level comprised of significant components of (a) spectroscopically-identifiable ammonia and (b) carbon-soot- impregnated condensates, observed above lightning storms near 35 [degrees] in both hemispheres. To obtain observations at depth, VIMS uses Saturnís indigenous thermal radiation at 5 [microns] to reveal meteorological features down to the 4-bar level of NH4SH cloud formation. As well, the Cassini /RADAR instrument is used in passive mode to map ammonia humidity at depth (~ 2-3 bar) near- simultaneously with VIMS. For both the equatorial plumes and the northern storm of 2010-2011, significant structure in ammonia humidity is observed, largely correlated with the VIMS clouds. The talk will discuss such observational results as well as present current ideas on the dynamics and chemistry behind these phenomena, including (time permitting): (1) Possible dynamical connections between the String of Pearls and the northern storm that erupted within it in December 2010, (2) the possible role of sequestration of NH3 in underlying water clouds to cause some equatorial plumes to appear remarkably NH3-dry, and (3) the role of lightning in creating carbon soot near the 10-20 bar level some 75-100 km below the visible cloudtops.

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