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Models of Saturn's Equatorial Ionosphere Based on In Situ Data From Cassini's Grand Finale
Author(s) -
Moore L.,
Cravens T. E.,
MüllerWodarg I.,
Perry M. E.,
Waite J. H.,
Perryman R.,
Nagy A.,
Mitchell D.,
Persoon A.,
Wahlund J.E.,
Morooka M. W.
Publication year - 2018
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2018gl078162
Subject(s) - saturn , ionosphere , ion , altitude (triangle) , physics , atmosphere (unit) , astrobiology , aeronomy , thermosphere , mass spectrometry , atmospheric sciences , astronomy , planet , meteorology , geometry , mathematics , quantum mechanics
We present new models of Saturn's equatorial ionosphere based on the first in situ measurements of its upper atmosphere. The neutral spectrum measured by Cassini's Ion and Neutral Mass Spectrometer, which includes substantial methane, ammonia, and organics in addition to the anticipated molecular hydrogen, helium, and water, serves as input for unexpectedly complex ionospheric chemistry. Heavy molecular ions are found to dominate Saturn's equatorial low‐altitude ionosphere, with a mean ion mass of 11 Da. Key molecular ions include H 3 O + and HCO + ; other abundant heavy ions depend upon the makeup of the mass 28 neutral species, which cannot be uniquely determined. Ion and Neutral Mass Spectrometer neutral species lead to generally good agreement between modeled and observed plasma densities, though poor reproduction of measured H + and H 3 + variability and an overabundance of modeled H 3 + potentially hint at missing physical processes in the model, including a loss process that affects H 3 + but not H + .