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

Moses, J. I.; Brown, Zarah; Koskinen, Tommi; Fletcher, Leigh N.; Serigano, Joseph; Guerlet, Sandrine; Moore, Luke; Waite, J. H.; Ben‐Jaffel, Lotfi; Galand, M.; Chadney, Joshua; Hörst, Sarah M.; Sinclair, James; Vuitton, V.; Mueller-Wodarg, Ingo

doi:10.1016/j.icarus.2022.115328

Cited by 10 publications

(26 citation statements)

References 180 publications

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“…(2020) and Moses et al. (2023) there is the possibility that a significant fraction of the neutrals detected by the INMS results from fast inflowing icy dust components vapourizing in the instrument. Moses et al.…”

Section: Resultsmentioning

confidence: 95%

“…X,H 3 + . These show lesser variation and agree somewhat better with the direct INMS measurements (Miller et al, 2020;Serigano et al, 2022a), especially when restricted to CH 4 , N 2 , and CO. A potential explanation for the latter could be similar to the basis for Case B as described by Moses et al (2023): Only the most volatile species enter the atmosphere as vapor, and most of the INMS data are due to impact fragmentation of grain-bound species, which are thus also not available for reactions in the ionosphere.…”

Section: 𝐴𝐴 𝐴𝐴mentioning

confidence: 99%

“…Consequently, number densities for heavier volatiles (e.g., H 2 O, CH 4 , NH 3 , CO 2 , N 2 , and CO) are not necessarily well constrained. Recent modeling efforts are not able to reproduce some of the expected effects of the measured high influxes of these species on the ionospheric and stratospheric chemistry (Moses et al., 2023). The aim of the present study is to present an alternative indirect method to constrain mixing ratios of heavier volatiles in Saturn's ionosphere.…”

Section: Introductionmentioning

confidence: 99%

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Utilizing Helium Ion Chemistry to Derive Mixing Ratios of Heavier Neutral Species in Saturn's Equatorial Ionosphere

et al. 2023

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A surprisingly strong influx of organic‐rich material into Saturn's upper atmosphere from its rings was observed during the proximal obits of the Grand Finale of the Cassini mission. Measurements by the Ion and Neutral Mass Spectrometer (INMS) gave insights into the composition of the material, but it remains to be resolved what fraction of the inferred heavy volatiles should be attributed as originating from the fragmentation of dust particles in the instrument versus natural ablation of grains in the atmosphere. In the present study, we utilize measured light ion and neutral densities to further constrain the abundances of heavy volatiles in Saturn's ionosphere through a steady‐state model focusing on helium ion chemistry. We first show that the principal loss mechanism of He+ in Saturn's equatorial ionosphere is through reactions with species other than H2. Based on the assumption of photochemical equilibrium at altitudes below 2,500 km, we then proceed by estimating the mixing ratio of heavier volatiles down to the closest approaches for Cassini's proximal orbits 288 and 292. Our derived mixing ratios for the inbound part of both orbits fall below those reported from direct measurements by the INMS, with values of ∼2 × 10−4 at closest approaches and order‐of‐magnitude variations in either direction over the orbits. This aligns with previous suggestions that a large fraction of the neutrals measured by the INMS stems from the fragmentation of infalling dust particles that do not significantly ablate in the considered part of Saturn's atmosphere and are thus unavailable for reactions.

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Section: Resultsmentioning

confidence: 95%

Section: 𝐴𝐴 𝐴𝐴mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Utilizing Helium Ion Chemistry to Derive Mixing Ratios of Heavier Neutral Species in Saturn's Equatorial Ionosphere

et al. 2023

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“…In the second step, we considered the possibility of H enhancement by influx of water and other species from the rings of the planet (Serigano et al 2022). The same photochemistry model shows that the corresponding H content is important (factor ∼1.75), yet such a large influx of water above 1.0 × 10 7 cm -2 s -1 seems inconsistent with UVIS occultation observations (Moses et al 2022).…”

Section: Discussionmentioning

confidence: 99%

“…During the grand finale orbits of Cassini, substantial influxes of water ((0.4-13.7) × 10 8 cm −2 s −1 ), methane ((7-25.7) × 10 8 cm −2 s −1 ), and other heavy species have been reported around the equatorial region, showing the complexity of the coupling between the rings and the Saturn ionosphere/upper atmosphere (Waite et al 2018;Yelle et al 2018;Serigano et al 2020). Such species modify the atmospheric structure and composition at specific latitudes (Yelle et al 2018;Moses et al 2022) and, according to the photochemistry model used here, enhance the H content. Independently, we also have a good indication of water precipitation from Enceladus into the upper atmosphere of Saturn, with an average downward flux of ∼1.5 × 10 6 cm −2 s −1 planet-wide (Moses et al 2000;Moore et al 2015).…”

Section: Model Comparison To Observationsmentioning

confidence: 99%

The Enigmatic Abundance of Atomic Hydrogen in Saturn’s Upper Atmosphere

et al. 2023

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A planet’s Lyα emission is sensitive to its thermospheric structure. Here we report joint Hubble Space Telescope and Cassini cross-calibration observations of the Saturn Lyα emission made 2 weeks before the Cassini grand finale. To investigate the long-term Saturn Lyα airglow observed by different ultraviolet instruments, we cross-correlate their calibration, finding that while the official Cassini/UVIS sensitivity should be lowered by ∼75%, the Voyager 1/UVS sensitivities should be enhanced by ∼20% at the Lyα channels. This comparison also allowed us to discover a permanent feature of the Saturn disk Lyα brightness that appears at all longitudes as a brightness excess (Lyα bulge) of ∼30% (∼12σ) extending over the latitude range ∼5°–35° N compared to the regions at equator and ∼60° N. This feature is confirmed by three distinct instruments between 1980 and 2017 in the Saturn north hemisphere. To analyze the Lyα observations, we use a radiation transfer model of resonant scattering of solar and interplanetary Lyα photons and a latitude-dependent photochemistry model of the upper atmosphere constrained by occultation and remote-sensing observations. For each latitude, we show that the Lyα observations are sensitive to the temperature profile in the upper stratosphere and lower thermosphere, thus providing useful information in a region of the atmosphere that is difficult to probe by other means. In the Saturn Lyα bulge region, at latitudes between ∼5° and ∼35°, the observed brightening and line broadening support seasonal effects, variation of the temperature vertical profile, and potential superthermal atoms that require confirmation.

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