Energy deposition in Saturn’s equatorial upper atmosphere

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

“…As can be seen, our background structure models have exospheric temperatures within a few degrees of previous analyses (Yelle et al, 2018;Waite et al, 2018;Chadney et al, 2022) and consider a thermal Yelle et al (2018). The orange curve is the Chadney et al (2022) 9.2 • latitude model, and the gray curves are various low-latitude (± 35 • ) temperature profiles derived from a combined analysis of UVIS occultations and CIRS limb retrievals from Brown et al (2021). Temperatures for our red and blue models at pressures greater than the horizontal dashed line are derived from our combined Cassini CIRS limb and nadir retrievals.…”

“…The above expression assumes that the atmospheric temperature and mean molecular mass are constant with radius over the limited radial range that is being used to determine the exospheric temperature from the INMS data -an assumption that is not strictly valid but that provides a reasonable structure model for our purposes. An alternative method would be to convert the vertical coordinate to gravitational potential (Yelle et al, 2018;Chadney et al, 2022;Serigano et al, 2022). As can be seen, our background structure models have exospheric temperatures within a few degrees of previous analyses (Yelle et al, 2018;Waite et al, 2018;Chadney et al, 2022) and consider a thermal Yelle et al (2018).…”

“…An alternative method would be to convert the vertical coordinate to gravitational potential (Yelle et al, 2018;Chadney et al, 2022;Serigano et al, 2022). As can be seen, our background structure models have exospheric temperatures within a few degrees of previous analyses (Yelle et al, 2018;Waite et al, 2018;Chadney et al, 2022) and consider a thermal Yelle et al (2018). The orange curve is the Chadney et al (2022) 9.2 • latitude model, and the gray curves are various low-latitude (± 35 • ) temperature profiles derived from a combined analysis of UVIS occultations and CIRS limb retrievals from Brown et al (2021).…”

“…Some of the consequences of this infalling ring-derived vapor and dust on Saturn's ionosphere have been discussed previously. Briefly, the inflow of neutral molecules from the rings causes heavy molecular ions with relatively short chemical lifetimes to supplant H + and H 3 + as the dominant ions near Saturn's main ionospheric peak at pressures ∼10 −6 -10 −7 mbar (Moore et al, 2018;Waite et al, 2018;Cravens et al, 2019;Dreyer et al, 2021;Chadney et al, 2022;Vigren et al, 2022), and incoming ring dust may influence ionospheric structure and charge balance (Mitchell et al, 2018;Hadid et al, 2019;Persoon et al, 2019;Morooka et al, 2019;Vigren et al, 2022;Johansson et al, 2022). From model-data comparisons and photochemical-equilibrium arguments, Dreyer et al (2021) find that the dominant heavy ion at low latitudes near 1700 km altitude should have an effective electron-recombination rate coefficient of ≲ 3 × 10 −7 at an electron temperature of 300 K, which makes HCO + a prime candidate for the dominant ion at the main peak (see also Moore et al, 2018).…”

Compositional Measurements of Saturn's Upper Atmosphere and Rings From Cassini INMS: An Extended Analysis of Measurements From Cassini's Grand Finale Orbits

“…This exogenous material, however, could play an important role in photochemistry and composition deeper in Saturn's atmosphere. Indeed, using INMS results from atmospheric entry, Chadney et al (2022) found that the addition of an influx of CH 4 into Saturn's thermosphere leads to photodissociated products in the region that could contribute to further chemistry and lead to the formation of higher mass molecules. Furthermore, Koskinen et al (2016) previously highlighted the idea of CH 4 photochemistry in the lower region of Saturn's ionosphere to initiate the chemistry that produces benzene and ultimately polycyclic aromatic HC and stratospheric haze in Saturn.…”