JWST/NIRSpec reveals the atmospheric driver of Saturn's variable magnetospheric rotation rate

Stallard, T.S. and Moore, Luke and Melin, Henrik and Smith, Chris G.A. and Agiwal, Omakshi and Chowdhury, M. Nahid and Johnson, Rosie E. and Knowles, Katie L. and Thomas, Emma M. and Tiranti, Paola I. and O'Donoghue, James and Mohamed, Khalid and Mueller‐Wodarg, Ingo and Coxon, John and Badman, Sarah and Caggiano, Joe A. (2026) JWST/NIRSpec reveals the atmospheric driver of Saturn's variable magnetospheric rotation rate. Journal of Geophysical Research: Space Physics. ISSN 2169-9402 (In Press)

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Abstract

Past measurements of Saturn's upper atmosphere have allowed only a broad scale view of the temperature and ion density structures within the auroral region. However, Saturn's auroral currents include a planetary period current component that is produced by neutral atmospheric flows. In order to understand the ultimate source for Saturn's planetary period aurora, we need vastly improved measurements of Saturn's auroral region. Here, using the first JWST/NIRSpec observations of Saturn, we reveal incredibly high spatial resolution ($<$500 km/pixel) views of Saturn's auroral region for the first time. This provides an at least an order-of-magnitude improvement in our measurement of the temperature and column density structure within Saturn's auroral region. It reveals an auroral region at the time of observation that is highly controlled by the planetary period currents, resulting in a series of upwards and downward currents from the pole to below the main auroral region. These are paired with reflected and inverted regions of heating and cooling across the auroral region. These patterns match surprisingly well to past model predictions, suggesting both the changes in column density and temperature are the direct result of localized heating positioned over the region of strongest particle precipitation. This strongly indicates that the planetary period currents are produced by a feedback loop, powered by the energy of magnetospherically generated aurora, preferentially heating one side of the auroral region.