Thermal Structure and Composition of Saturn's Upper Atmosphere From Cassini/Ion Neutral Mass Spectrometer Measurements

Roger V. Yelle; J. Serigano; T. T. Koskinen; S. M. Hörst; M. E. Perry; R. S. Perryman; J. Hunter Waite

doi:10.1029/2018GL078454

Thermal Structure and Composition of Saturn's Upper Atmosphere From Cassini/Ion Neutral Mass Spectrometer Measurements

Roger V. Yelle, J. Serigano, T. T. Koskinen, S. M. Hörst, M. E. Perry, R. S. Perryman, J. Hunter Waite

Research output: Contribution to journal › Article › peer-review

22 Scopus citations

Abstract

Analysis of measurements of the H₂ density in Saturn's equatorial thermosphere indicates temperatures from 340 to 370 K. The deepest measurements, obtained during Cassini's final plunge into the atmosphere, measure the thermospheric temperature profile. The measurements are well fit by a Bates profile with an exospheric temperature of 354 K and a temperature gradient at 1.2 × 10⁻⁴ Pa of 0.4 K/km, corresponding to a thermal conduction flux of 7.3 × 10⁻⁵ W/m². The helium profiles are consistent with diffusive equilibrium. The CH₄ profiles are not in diffusive equilibrium but instead have a roughly constant mixing ratio relative to H₂. We interpret this as the signature of a downward external flux of ∼10¹³ m⁻² s⁻¹. Saturn's rings are the most likely source of this external material.

Original language	English (US)
Pages (from-to)	10,951-10,958
Journal	Geophysical Research Letters
Volume	45
Issue number	20
DOIs	https://doi.org/10.1029/2018GL078454
State	Published - Oct 28 2018

Keywords

Saturn
aeronomy
composition
rings
thermosphere

ASJC Scopus subject areas

Geophysics
General Earth and Planetary Sciences

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10.1029/2018GL078454

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@article{6e66487048534509995b04876b61dd1c,

title = "Thermal Structure and Composition of Saturn's Upper Atmosphere From Cassini/Ion Neutral Mass Spectrometer Measurements",

abstract = "Analysis of measurements of the H2 density in Saturn's equatorial thermosphere indicates temperatures from 340 to 370 K. The deepest measurements, obtained during Cassini's final plunge into the atmosphere, measure the thermospheric temperature profile. The measurements are well fit by a Bates profile with an exospheric temperature of 354 K and a temperature gradient at 1.2 × 10−4 Pa of 0.4 K/km, corresponding to a thermal conduction flux of 7.3 × 10−5 W/m2. The helium profiles are consistent with diffusive equilibrium. The CH4 profiles are not in diffusive equilibrium but instead have a roughly constant mixing ratio relative to H2. We interpret this as the signature of a downward external flux of ∼1013 m−2 s−1. Saturn's rings are the most likely source of this external material.",

keywords = "Saturn, aeronomy, composition, rings, thermosphere",

author = "Yelle, {Roger V.} and J. Serigano and Koskinen, {T. T.} and H{\"o}rst, {S. M.} and Perry, {M. E.} and Perryman, {R. S.} and Waite, {J. Hunter}",

note = "Funding Information: The research described in this paper has been supported by NASA Prime contract NAS7-03001 under JPL subcontract 1405853 to the Southwest Research Institute and SWRI subcontract to the University of Arizona. We acknowledge the resolute planning and execution by the Cassini spacecraft operations team in obtaining the data from the proximal orbits. The data analyzed here is archived in the Planetary Data System. Publisher Copyright: {\textcopyright}2018. American Geophysical Union. All Rights Reserved.",

year = "2018",

month = oct,

day = "28",

doi = "10.1029/2018GL078454",

language = "English (US)",

volume = "45",

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journal = "Geophysical Research Letters",

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AU - Yelle, Roger V.

AU - Serigano, J.

AU - Koskinen, T. T.

AU - Hörst, S. M.

AU - Perry, M. E.

AU - Perryman, R. S.

AU - Waite, J. Hunter

N1 - Funding Information: The research described in this paper has been supported by NASA Prime contract NAS7-03001 under JPL subcontract 1405853 to the Southwest Research Institute and SWRI subcontract to the University of Arizona. We acknowledge the resolute planning and execution by the Cassini spacecraft operations team in obtaining the data from the proximal orbits. The data analyzed here is archived in the Planetary Data System. Publisher Copyright: ©2018. American Geophysical Union. All Rights Reserved.

PY - 2018/10/28

Y1 - 2018/10/28

N2 - Analysis of measurements of the H2 density in Saturn's equatorial thermosphere indicates temperatures from 340 to 370 K. The deepest measurements, obtained during Cassini's final plunge into the atmosphere, measure the thermospheric temperature profile. The measurements are well fit by a Bates profile with an exospheric temperature of 354 K and a temperature gradient at 1.2 × 10−4 Pa of 0.4 K/km, corresponding to a thermal conduction flux of 7.3 × 10−5 W/m2. The helium profiles are consistent with diffusive equilibrium. The CH4 profiles are not in diffusive equilibrium but instead have a roughly constant mixing ratio relative to H2. We interpret this as the signature of a downward external flux of ∼1013 m−2 s−1. Saturn's rings are the most likely source of this external material.

AB - Analysis of measurements of the H2 density in Saturn's equatorial thermosphere indicates temperatures from 340 to 370 K. The deepest measurements, obtained during Cassini's final plunge into the atmosphere, measure the thermospheric temperature profile. The measurements are well fit by a Bates profile with an exospheric temperature of 354 K and a temperature gradient at 1.2 × 10−4 Pa of 0.4 K/km, corresponding to a thermal conduction flux of 7.3 × 10−5 W/m2. The helium profiles are consistent with diffusive equilibrium. The CH4 profiles are not in diffusive equilibrium but instead have a roughly constant mixing ratio relative to H2. We interpret this as the signature of a downward external flux of ∼1013 m−2 s−1. Saturn's rings are the most likely source of this external material.

KW - Saturn

KW - aeronomy

KW - composition

KW - rings

KW - thermosphere

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Thermal Structure and Composition of Saturn's Upper Atmosphere From Cassini/Ion Neutral Mass Spectrometer Measurements

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