1 nm ) solar spectra, as long as high-resolution cross sections are included in the model.īetween April and September 2017, after spending 13 years exploring the Kronian system, the Cassini spacecraft performed 23 proximal orbits passing within Saturn’s D ring, allowing us to directly probe the upper atmosphere of a gas giant planet. We find that these peaks are still formed when using low-resolution ( Δ λ = 1 nm) or mid-resolution ( Δ λ = 0. We assess the importance of spectral resolution in the energy deposition model by using a high-resolution H 2 photo-absorption cross section, which has the effect of producing additional ionisation peaks near 800 km altitude. The ion reaction rate profiles we determine are important to obtain accurate ion density profiles, meanwhile methane photo-dissociation is key to initiate complex organic chemical processes. Our energy deposition model calculates ion production rate profiles through photo-ionisation and electron-impact ionisation processes, as well as rates of photo-dissociation of CH 4. These neutral profiles are fed into an energy deposition model employing soft X-ray and Extreme UltraViolet (EUV) solar fluxes at a range of spectral resolutions ( Δ λ = 4 × 1 0 − 3 nm to 1 nm) assembled from TIMED/SEE, from SOHO/SUMER, and from the Whole Heliosphere Interval (WHI) quiet Sun campaign. ![]() We construct Saturn equatorial neutral temperature and density profiles of H, H 2, He, and CH 4, between 10 −12 and 1 bar using measurements from Cassini’s Ion Neutral Mass Spectrometer (INMS) taken during the spacecraft’s final plunge into Saturn’s atmosphere on 15 September 2017, combined with previous deeper atmospheric measurements from the Cassini Composite InfraRed Spectrometer (CIRS) and from the UltraViolet Imaging Spectrograph (UVIS).
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