# Implications of the Cassini Grand Finale INMS measurements for atmospheric chemistry on Saturn (and vice versa)

Julianne Moses, Zarah Brown, Tommi Koskinen, Leigh Fletcher, Sandrine

Guerlet, Joseph Serigano, Luke Moore, J. Hunter Hunter Waite, Lotfi

Ben-Jaffel, Marina Galand, et al.

► To cite this version:

Julianne Moses, Zarah Brown, Tommi Koskinen, Leigh Fletcher, Sandrine Guerlet, et al.. Implications of the Cassini Grand Finale INMS measurements for atmospheric chemistry on Saturn (and vice versa). 55th Annual Meeting of the Division for Planetary Sciences, Oct 2023, San Antonio, United States. hal-04788773

HAL Id: hal-04788773

https://hal.science/hal-04788773v1

Submitted on 18 Nov 2024

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# Implications of the Cassini Grand Finale INMS measurements for atmospheric chemistry on Saturn (and vice versa)

Julianne Moses<fnref n="1" /> Zarah Brown² Tommi Koskinen² Leigh Fletcher³

Sandrine Guerlet<fnref n="4" /> Joseph Serigano⁵ Luke Moore⁶ J. Hunter Waite<fnref n="7" />

Lotfi Ben-Jaffel⁸ Marina Galand⁹ Joshua Chadney⁹ Sarah Horst⁵

James Sinclair<fnref n="10" /> Veronique Vuitton¹¹ Ingo Mueller-Wodarg⁹

<footnote n="1">¹Space Science Institute, ²University of Arizona, ³University of Leicester,</footnote>

<footnote n="4">⁴Laboratoire de Meteorologie Dynamique, ⁵Johns Hopkins University, ⁶Boston Univ.,</footnote>

<footnote n="7">⁷Southwest Research Institute, ⁸IAP-CNRS, ⁹Imperial College London,</footnote>

<footnote n="10">¹⁰Jet Propulsion Laboratory/Caltech, ¹¹Univ. Grenoble Alpes, CNRS, IPAG</footnote>
*In situ* measurements from the Ion and Neutral Mass Spectrometer (INMS) instrument during the Grand Finale stage of the *Cassini* mission have revealed surprisingly large amounts of ring material flowing into Saturn's equatorial upper atmosphere. Our photochemical models indicate that the composition of Saturn's ionosphere and neutral stratosphere would be significantly affected by this incoming material if a large fraction of the ring debris were entering the atmosphere as vapor, or if solid ring particles were vaporized during entry. However, the observational consequences predicted by these models are not evident in our surveys of *Cassini* infrared and ultraviolet remote-sensing data from the last years of the *Cassini* mission. This lack of evidence for ring-derived molecules in the lower thermosphere and stratosphere suggests that either the inflow inferred by INMS derives from a recent dynamical event in the ring system that occurred a few months to a few years before the 2017 measurements, or that the incoming material derives predominantly from small dust particles (less than 100 nm radius) that are entering the atmosphere slowly enough to avoid ablating. If a recent but continuing ring event is the culprit, the abundance of HC₃N and HCN could build up to become observable within the next few years, and the CO₂ abundance could be enhanced over what was seen during the *Cassini* mission.
Future infrared observations or upper limits for these molecules in Saturn's stratosphere could shed light on the origin, timing, magnitude, and nature of Saturn's ring-atmosphere interaction. Regarding this point, we note that *JWST* observations from Saturn in 2022 did not see any evidence for the expected species (Fletcher et al. 2023), further reinforcing the dust hypothesis or the very transient nature of the event.

More information can be found at https://www.sciencedirect.com/science/article/pii/S0019103522004201?via%3Dihub