Energy deposition in Saturn's equatorial upper atmosphere
File(s)Chadney_etal_2021.pdf (2.57 MB)
Accepted version
Author(s)
Type
Journal Article
Abstract
We construct Saturn equatorial neutral temperature and density profiles of H, H2, He, and CH4, 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). 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 (∆λ = 4×10−3 nm to 1 nm) assembled from TIMED/SEE, from SOHO/SUMER, and from the Whole Heliosphere Interval (WHI) quiet Sun campaign. 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 CH4. 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. We assess the importance of spectral resolution in the energy deposition model by using a high-resolution H2 photo-absorption cross section, which has the effect of producing additional ionisation peaks near 800 km altitude. We find that these peaks are still formed when using low resolution (∆λ = 1 nm) or mid-resolution (∆λ = 0.1 nm) solar spectra, as long as high-resolution cross sections are included in the model.
Date Issued
2022-01-15
Date Acceptance
2021-09-27
Citation
Icarus, 2022, 372, pp.1-16
ISSN
0019-1035
Publisher
Elsevier
Start Page
1
End Page
16
Journal / Book Title
Icarus
Volume
372
Copyright Statement
This paper is embargoed until 12 months after publication.
Sponsor
Science and Technology Facilities Council (STFC)
Identifier
https://www.sciencedirect.com/science/article/pii/S0019103521003791?via%3Dihub
Grant Number
ST/N000692/1
Subjects
astro-ph.EP
astro-ph.EP
physics.space-ph
Astronomy & Astrophysics
0201 Astronomical and Space Sciences
0402 Geochemistry
0404 Geophysics
Publication Status
Published
Article Number
114724
Date Publish Online
2021-10-15