JWST/NIRSpec Detection of Complex Structures in Saturn's Sub-Auroral Ionosphere and Stratosphere

Tom S. Stallard; Luke Moore; Henrik Melin; Omakshi Agiwal; M. Nahid Chowdhury; Rosie E. Johnson; Katie L. Knowles; Emma M. Thomas; Paola I. Tiranti; James O’Donoghue; Khalid Mohamed; Ingo Mueller‐Wodarg; Leigh Fletcher; Imke de Pater; Thierry Fouchet; Sarah V. Badman

doi:10.1029/2025gl116491

JWST/NIRSpec Detection of Complex Structures in Saturn's Sub-Auroral Ionosphere and Stratosphere

Tom S. Stallard^*, Luke Moore, Henrik Melin, Omakshi Agiwal, M. Nahid Chowdhury, Rosie E. Johnson, Katie L. Knowles, Emma M. Thomas, Paola I. Tiranti, James O’Donoghue, Khalid Mohamed, Ingo Mueller‐Wodarg, Leigh Fletcher, Imke de Pater, Thierry Fouchet, Sarah V. Badman

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Department of Physics

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Abstract

Past observations of Saturn's sub-auroral ionosphere have provided no detailed longitudinal information, and variations in underlying stratospheric emission from methane fluorescence have never been resolved spatially. Here, we present the first near-infrared observations of Saturn using JWST's NIRSpec-IFU, revealing the 2.8–5.2 micron wavelength region in unprecedented detail. We observe the rotating auroral enhancement associated with planetary-period currents, the phase of which is re-discovered for the first time since Cassini. We discover a series of ionospheric dark beads located between 55 and 65 (Formula presented.) N, that appear to be formed by local thermospheric dynamics. In the fluorescing methane, we reveal strange dark arms extending equatorward from a dark polar cap at 60 (Formula presented.) N; four arms from a six-pointed star, each extend below 45 (Formula presented.) N with the final two arms missing. Neither set of features has any known analog at other planets.

Original language	English
Article number	e2025GL116491
Number of pages	9
Journal	Geophysical Research Letters
Volume	52
Issue number	17
Early online date	28 Aug 2025
DOIs	https://doi.org/10.1029/2025gl116491
Publication status	Published - 16 Sept 2025

Keywords

rotation period
aurora
stratosphere
Saturn
JWST
ionosphere

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ArticleFinal published version, 1.75 MBLicence: CC BY
Supporting informationData, 207 KBLicence: CC BY

https://mast.stsci.edu/search/ui/#/jwst/results?program_id=5308

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Stallard, T. S., Moore, L., Melin, H., Agiwal, O., Chowdhury, M. N., Johnson, R. E., Knowles, K. L., Thomas, E. M., Tiranti, P. I., O’Donoghue, J., Mohamed, K., Mueller‐Wodarg, I., Fletcher, L., de Pater, I., Fouchet, T., & Badman, S. V. (2025). JWST/NIRSpec Detection of Complex Structures in Saturn's Sub-Auroral Ionosphere and Stratosphere. Geophysical Research Letters, 52(17), Article e2025GL116491. https://doi.org/10.1029/2025gl116491

@article{7e4a7f9d3d614cadb24f277441b52c73,

title = "JWST/NIRSpec Detection of Complex Structures in Saturn's Sub-Auroral Ionosphere and Stratosphere",

abstract = "Past observations of Saturn's sub-auroral ionosphere have provided no detailed longitudinal information, and variations in underlying stratospheric emission from methane fluorescence have never been resolved spatially. Here, we present the first near-infrared observations of Saturn using JWST's NIRSpec-IFU, revealing the 2.8–5.2 micron wavelength region in unprecedented detail. We observe the rotating auroral enhancement associated with planetary-period currents, the phase of which is re-discovered for the first time since Cassini. We discover a series of ionospheric dark beads located between 55 and 65 (Formula presented.) N, that appear to be formed by local thermospheric dynamics. In the fluorescing methane, we reveal strange dark arms extending equatorward from a dark polar cap at 60 (Formula presented.) N; four arms from a six-pointed star, each extend below 45 (Formula presented.) N with the final two arms missing. Neither set of features has any known analog at other planets.",

keywords = "rotation period, aurora, stratosphere, Saturn, JWST, ionosphere",

author = "Stallard, \{Tom S.\} and Luke Moore and Henrik Melin and Omakshi Agiwal and Chowdhury, \{M. Nahid\} and Johnson, \{Rosie E.\} and Knowles, \{Katie L.\} and Thomas, \{Emma M.\} and Tiranti, \{Paola I.\} and James O{\textquoteright}Donoghue and Khalid Mohamed and Ingo Mueller‐Wodarg and Leigh Fletcher and \{de Pater\}, Imke and Thierry Fouchet and Badman, \{Sarah V.\}",

note = "{\textcopyright} 2025. The Author(s).",

year = "2025",

month = sep,

day = "16",

doi = "10.1029/2025gl116491",

language = "English",

volume = "52",

journal = "Geophysical Research Letters",

issn = "0094-8276",

publisher = "Wiley",

number = "17",

}

Stallard, TS, Moore, L, Melin, H, Agiwal, O, Chowdhury, MN, Johnson, RE, Knowles, KL, Thomas, EM, Tiranti, PI, O’Donoghue, J, Mohamed, K, Mueller‐Wodarg, I, Fletcher, L, de Pater, I, Fouchet, T & Badman, SV 2025, 'JWST/NIRSpec Detection of Complex Structures in Saturn's Sub-Auroral Ionosphere and Stratosphere', Geophysical Research Letters, vol. 52, no. 17, e2025GL116491. https://doi.org/10.1029/2025gl116491

TY - JOUR

T1 - JWST/NIRSpec Detection of Complex Structures in Saturn's Sub-Auroral Ionosphere and Stratosphere

AU - Stallard, Tom S.

AU - Moore, Luke

AU - Melin, Henrik

AU - Agiwal, Omakshi

AU - Chowdhury, M. Nahid

AU - Johnson, Rosie E.

AU - Knowles, Katie L.

AU - Thomas, Emma M.

AU - Tiranti, Paola I.

AU - O’Donoghue, James

AU - Mohamed, Khalid

AU - Mueller‐Wodarg, Ingo

AU - Fletcher, Leigh

AU - de Pater, Imke

AU - Fouchet, Thierry

AU - Badman, Sarah V.

PY - 2025/9/16

Y1 - 2025/9/16

N2 - Past observations of Saturn's sub-auroral ionosphere have provided no detailed longitudinal information, and variations in underlying stratospheric emission from methane fluorescence have never been resolved spatially. Here, we present the first near-infrared observations of Saturn using JWST's NIRSpec-IFU, revealing the 2.8–5.2 micron wavelength region in unprecedented detail. We observe the rotating auroral enhancement associated with planetary-period currents, the phase of which is re-discovered for the first time since Cassini. We discover a series of ionospheric dark beads located between 55 and 65 (Formula presented.) N, that appear to be formed by local thermospheric dynamics. In the fluorescing methane, we reveal strange dark arms extending equatorward from a dark polar cap at 60 (Formula presented.) N; four arms from a six-pointed star, each extend below 45 (Formula presented.) N with the final two arms missing. Neither set of features has any known analog at other planets.

AB - Past observations of Saturn's sub-auroral ionosphere have provided no detailed longitudinal information, and variations in underlying stratospheric emission from methane fluorescence have never been resolved spatially. Here, we present the first near-infrared observations of Saturn using JWST's NIRSpec-IFU, revealing the 2.8–5.2 micron wavelength region in unprecedented detail. We observe the rotating auroral enhancement associated with planetary-period currents, the phase of which is re-discovered for the first time since Cassini. We discover a series of ionospheric dark beads located between 55 and 65 (Formula presented.) N, that appear to be formed by local thermospheric dynamics. In the fluorescing methane, we reveal strange dark arms extending equatorward from a dark polar cap at 60 (Formula presented.) N; four arms from a six-pointed star, each extend below 45 (Formula presented.) N with the final two arms missing. Neither set of features has any known analog at other planets.

KW - rotation period

KW - aurora

KW - stratosphere

KW - Saturn

KW - JWST

KW - ionosphere

UR - https://www.scopus.com/pages/publications/105014619859

U2 - 10.1029/2025gl116491

DO - 10.1029/2025gl116491

M3 - Article

SN - 0094-8276

VL - 52

JO - Geophysical Research Letters

JF - Geophysical Research Letters

IS - 17

M1 - e2025GL116491

ER -

JWST/NIRSpec Detection of Complex Structures in Saturn's Sub-Auroral Ionosphere and Stratosphere

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