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

TL;DR

This study investigates the impact of ring material influx into Saturn's atmosphere during Cassini's final phase, finding no expected chemical signatures and suggesting the influx was either transient or composed mainly of small dust particles.

Contribution

It provides the first analysis linking Cassini's INMS measurements with atmospheric chemistry models and remote sensing data to understand ring material influx effects.

Findings

No chemical signatures of ring influx detected in Saturn's atmosphere.

The ring influx was likely transient or composed mainly of small dust particles.

Future observations could clarify the nature of the ring material influx.

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.