Saturn's atmospheric response to the large influx of ring material inferred from Cassini INMS measurements

Abstract

During the Grand Finale stage of the Cassini mission, organic-rich ring material was discovered to be flowing into Saturn's equatorial upper atmosphere at a surprisingly large rate. Through a series of photochemical models, we have examined the consequences of this ring material on the chemistry of Saturn's neutral and ionized atmosphere. We find that if a substantial fraction of this material enters the atmosphere as vapor or becomes vaporized as the solid ring particles ablate upon atmospheric entry, then the ring-derived vapor would strongly affect the composition of Saturn's ionosphere and neutral stratosphere. Our surveys of Cassini infrared and ultraviolet remote-sensing data from the final few years of the mission, however, reveal none of these predicted chemical consequences. We therefore conclude that either (1) the inferred ring influx represents an anomalous, transient situation that was triggered by some recent dynamical event in the ring system that occurred a few months to a few tens of years before the 2017 end of the Cassini mission, or (2) a large fraction of the incoming material must have been entering the atmosphere as small dust particles less than ~100 nm in radius, rather than as vapor or as large particles that are likely to ablate. Future observations or upper limits for stratospheric neutral species such as HC${}_3$N, HCN, and CO${}_2$ at infrared wavelengths could shed light on the origin, timing, magnitude, and nature of a possible vapor-rich ring-inflow event.

arXiv commentaccepted in Icarus

References in corpus (18)

• Disequilibrium Carbon, Oxygen, and Nitrogen Chemistry in the Atmospheres of HD 189733b and HD 209458b
• The Deep Water Abundance on Jupiter: New Constraints from Thermochemical Kinetics and Diffusion Modeling
• Dust Ablation on the Giant Planets: Consequences for Stratospheric Photochemistry
• Chemical Constraints on the Water and Total Oxygen Abundances in the Deep Atmosphere of Saturn
• The domination of Saturn's low latitude ionosphere by ring `rain'
• Models of Saturn's Interior Constructed with Accelerated Concentric Maclaurin Spheroid Method
• Seasonal stratospheric photochemistry on Uranus and Neptune
• Modeling the disequilibrium species for Jupiter and Saturn: Implications for Juno and Saturn entry probe
• Seasonal Evolution of Saturn's Polar Temperatures and Composition
• On the abundance of non-cometary HCN on Jupiter
• A pole to pole pressure temperature map of Saturn's thermosphere from Cassini Grand Finale data
• Saturn's upper atmosphere during the Voyager era: Reanalysis and modeling of the UVS occultations
• Herschel map of Saturn's stratospheric water, delivered by the plumes of Enceladus
• 1D photochemical model of the ionosphere and the stratosphere of Neptune
• Compositional Measurements of Saturn's Upper Atmosphere and Rings from Cassini INMS
• Energy deposition in Saturn's equatorial upper atmosphere
• Implications from secondary emission from neutral impact on Cassini plasma and dust measurements
• Bright clumps in the D68 ringlet near the end of the Cassini Mission

Cited by in corpus (3)

• Saturn's Atmosphere in Northern Summer Revealed by JWST/MIRI
• The enigmatic abundance of atomic hydrogen in Saturn's upper atmosphere
• Seasonal variation of Saturn's Lyman-$\alpha$ brightness