JWST/NIRSpec detection of complex structures in Saturn's sub‐auroral ionosphere and stratosphere

Stallard, T. S., Moore, L., Melin, H., Agiwal, O., Nahid Chowdhury, M., Johnson, R. E., Knowles, K. L., Thomas, E. M., Tiranti, P. I., O'Donoghue, J. ORCID: https://orcid.org/0000-0002-4218-1191, Mohamed, K., Mueller‐Wodarg, I., Fletcher, L., de Pater, I., Fouchet, T. and Badman, S. V. (2025) JWST/NIRSpec detection of complex structures in Saturn's sub‐auroral ionosphere and stratosphere. Geophysical Research Letters, 52 (17). e2025GL116491. ISSN 0094-8276 doi: 10.1029/2025GL116491

Abstract/Summary

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°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°N; four arms from a six‐pointed star, each extend below 45°N with the final two arms missing. Neither set of features has any known analog at other planets.

Item Type	Article
URI	https://centaur.reading.ac.uk/id/eprint/124135
Identification Number/DOI	10.1029/2025GL116491
Refereed	Yes
Divisions	Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
Publisher	American Geophysical Union
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