Ingo Mueller-Wodarg

We use JAMMIES (JAMMIES is Another Model Making Ionospheric EStimates), a new model of Jupiter's non‐auroral ionosphere, to demonstrate that neutral wind‐driven field‐aligned plasma transport can explain decades of measurements inconsistent with a solar‐dominated ionosphere. Two observations highlight these inconsistencies: a minimum in emission along the magnetic equator where solar ionization maximizes, and a systematic asymmetry where vertical dawn plasma densities exceed those at dusk. JAMMIES models the chemical and dynamical evolution of plasma in a dipole coordinate system. Observed emissions can be reproduced via two mechanisms: (i) field‐aligned neutral‐ion collisions driven by a steady‐state global neutral wind pattern, or (ii) field‐perpendicular electrodynamic plasma drifts at the magnetic equator. Mechanism (i), induced by persistent auroral heating, also reproduces disparate vertical plasma profiles. Results show that neutral wind‐driven dynamics dominate Jovian ionospheric structure, which is found to be spatially variable but temporally stable.

Jupiter’s upper atmosphere (mesosphere/thermosphere/ionosphere) is driven primarily by its interaction with the magnetosphere which maps an electric potential into the magnetic polar region and is accompanied by energetic electron precipitation into the upper atmosphere. While the latter significantly contributes towards the ionospheric densities, the former generates westward accelerations at auroral latitudes and a transfer of angular momentum from atmosphere to magnetosphere as well as local Joule heating. In-situ solar heating is insignificant in the upper atmosphere, but the solar ionization plays a key role especially at non-auroral latitudes. Over the past years, we have developed the Jupiter Thermosphere Ionosphere Model (JTIM) (Mueller-Wodarg et al., 2025) to numerically calculate this time-dependent coupling and test the sensitivity of the global atmosphere system to forcing from the magnetosphere interaction. With JTIM, we calculate the global dynamics and redistribution of energy. Most recently, we have updated the JTIM model with more realistic electric potentials from the BATSrU model (Sarkango et al., 2019) and electron impact ionization rates from the Jupiter Auroral Ionosphere Code (JAIC) (Nichols et al., 2026). We will present latest simulations and compare with available observations. Our calculations allow us to better understand the underlying physical processes in this complex system, including the role of coupling with the deeper atmosphere and global distribution and transport of angular momentum as well as variability of the entire system.

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 James Webb Space Telescope (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 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.

Solar energetic events can have considerable effects on planetary ionospheres. However, the erratic nature of these solar energetic events make observations difficult. Here we show a mutual radio occultation observation, which serendipitously occurred just 10 minutes after a large solar flare impacted Mars. This resulted in the largest lower ionospheric layer ever recorded, where it was 278% its typical size. We used in-situ soft x-ray irradiance measurements to show a threefold increase in flux. This infers a different relation of soft X-ray to this layer’s density than previously thought, with variations depending on the amount of spectrum ‘hardening’ leading to the increase of ionisation from secondaries.

Planetary upper atmospheres couple the deep atmosphere to the space environment. The dynamics and energetics of this rarefied, partially ionized region govern atmospheric evolution. At Jupiter, decades of past plasma measurements have revealed a variable and enigmatic ionosphere inconsistent with photochemical predictions and unusual global structures imprinted by the planet’s powerful magnetic field. Upper-atmospheric temperatures have been measured sporadically and thus are unable to fully characterize the energy transfer mechanism responsible for its unexpectedly hot thermosphere. Observations to date have been too limited spatially, or too insensitive, to uncover the driving mechanisms behind the strong variability and magnetically organized features found in Jupiter’s upper atmosphere. Here, we present high spatial resolution global maps of ion densities and temperatures constructed from >175,000 Keck/NIRSPEC spectra collected over 4 yr. Irregular ionospheric emission features, first seen more than 25 yr ago, are shown to be persistent and due to local ion density modifications. Global temperatures decrease steadily from auroral to equatorial latitudes and are remarkably stable, with equatorial deviations of <10% night to night. Thus, despite appearing stochastic in previous observations, Jupiter’s upper atmosphere exhibits predominantly spatial rather than temporal variability, yielding a steady global structure generated by local plasma dynamics. These results illustrate how neutral winds and magnetic fields can create globally persistent plasma structures on hydrogen-dominated worlds and provide an explanation for decades of puzzling Jovian upper-atmospheric observations.

Observations of continuous vertical electron and ion distributions at Jupiter were obtained simultaneously for the first time on 2023 September 7 UTC. On that date, Juno performed a radio occultation experiment and, in parallel, JWST and Keck scanned Jupiter’s limb, focused on characterizing H 3 + . Here, using Keck infrared spectra, we derive constraints on H 3 + densities and temperatures. While on-disk column densities are roughly constant with latitude, with a mean value of (5.7 ± 2.1) × 10 ¹⁵ m ⁻² , temperatures decrease smoothly from 774 ± 50 K at high latitude to 683 ± 28 K at low latitude. Vertical H 3 + temperatures are comparable to their on-disk values and mostly isothermal. Keck spectra sampled Jupiter’s dawn limb, finding H 3 + volumetric number densities of (1–40) × 10 ⁸ m ⁻³ with peak altitudes near 1500 km. Comparison with the Juno electron altitude density profile confirms Jupiter’s ionosphere is proton dominated. Ionospheric model simulations that can broadly replicate observed plasma densities indicate that field-aligned vertical transport driven by neutral winds is primarily responsible for the observed high-altitude peak. We use model outputs, validated by comparison with plasma observations, to demonstrate that H 3 + is in photochemical equilibrium (PCE) below ∼1600 km altitude in Jupiter’s ionosphere. PCE analysis further reveals that the diurnal peak in N H 3 + can occur before noon, that peak electron densities should generally be 11 m ⁻³ , and that rapidly varying auroral H 3 + emissions can be explained by narrow ( 3 + just above the homopause produced by energetic particle precipitation.

This study investigates the non‐solar trends and variability in Jupiter's sub‐auroral ionosphere from Pioneer, Voyager, Galileo, and Juno radio occultation electron density profiles. We show that these data are correlated with magnetic field geometry via primarily westward and equatorward thermospheric neutral winds driving field‐aligned plasma transport. This process separates Jupiter's ionosphere into variable vertical plasma drift regions, which organize most of the observed spatial and local time variability in electron density data. However, the ionospheric structure appears to be more variable when wind‐driven transport is weak, shaped by additional drivers that need further investigation. Nonetheless, Jupiter's sub‐auroral ionosphere appears to primarily be a closed system with remarkably stable vertical structure over 6 decades.

This study investigates the non-solar trends and variability in Jupiter’s sub-auroral ionosphere from Pioneer, Voyager, Galileo, and Juno radio occultation electron density profiles. We show that these data are correlated with magnetic field geometry via primarily westward and equatorward thermospheric neutral winds driving field-aligned plasma transport. This process separates Jupiter’s ionosphere into variable vertical plasma drift regions, which organize most of the observed spatial and local time variability in electron density data. However, the ionospheric structure appears to be more variable when wind-driven transport is weak, shaped by additional drivers that need further investigation. Nonetheless, Jupiter’s sub-auroral ionosphere appears to primarily be a closed system with remarkably stable structure over ~6 decades.

The primary source of heating in the upper atmospheres (thermospheres) of giant planets has been the subject of long debate. The conundrum (or “energy crisis”) consists in observed thermosphere temperatures at low and midlatitudes exceeding values expected from solar heating by several hundred kelvins, suggesting the presence of another energy source. Several theories have been proposed to explain the high temperatures, from heating by upward-propagating gravity or acoustic waves to heating of auroral regions by magnetosphere–atmosphere coupling. While auroral heating provides sufficient energy, the problem becomes one of global energy redistribution. On a rapidly rotating planet, Coriolis forces act to “trap” auroral energy in the polar regions, heating up the poles but leaving the equator cold. On Saturn, the redistribution of energy from poles to equator was recently achieved by invoking Rayleigh drag, possibly related to atmospheric gravity or acoustic waves. Using a new general circulation model of Jupiter, we reproduce well the observed low and midlatitude thermosphere temperatures without the need to invoke Rayleigh drag. Instead, the planet’s magnetic field is strong enough to cause significant ion drag and slowing down zonal winds in the nonauroral thermosphere and allow global energy redistribution. This distinguishes Jupiter from Saturn and most likely the other gas giant planets in our solar system may have implications on extrasolar planets with strong magnetic fields as well.

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 65N, 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 60N; four arms from a six‐pointed star, each extend below 45N with the final two arms missing. Neither set of features has any known analog at other planets.