Photochemistry in Saturn's Ring-Shadowed Atmosphere: Photochemical and Haze Production
Abstract
After 13 years of observing Saturn, Cassini explored for nearly a half Saturnian year. During this epoch, in addition to seasonal solar inclination changes, the ring shadow has moved from covering much of the northern hemisphere to covering a large swath of the southern hemisphere. The intensity of both ultraviolet and visible sunlight penetrating through the rings varied depending on Saturn's axial tilt relative to the Sun and the optical thickness of each ring system, i.e. the rings act like semi-transparent venetian blinds. This effect magnifies the effect of axial tilt alone and acts to turn off photochemistry and haze generation, an effect seen with the presence of a bluish northern atmosphere in 2004 and color change to blue in the southern hemisphere after equinox. We report on the impact of the oscillating ring shadow, seasonal axial tilt, and solar flux, on photochemistry of hydrocarbons and phosphine in Saturn's stratosphere and upper troposphere. The impact on the abundance of long-lived photochemical products leading to haze formation and on disequilibrium species is explored.We will also present analysis of Cassini's CIRS, UVIS, and VIMS datasets that provide an estimate of the evolving haze content. Specifically, we will examine how the region inside Saturn's famous hexagonal jet stream evolves over time from a relatively clear atmosphere to hazy atmosphere and how the jet stream acts like a barrier to transport, thus isolating Saturn's north polar region from outside influences. Lastly, an estimate of the impact of ultraviolet ring-shine on photochemistry is provided.The research described in this paper was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Copyright 2018 California Institute of Technology. Government sponsorship is acknowledged.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E.948E