JWST Cycle 4 observations of Jupiter’s polar region:Constraining temperature and hydrocarbon abundances

The James Webb Space Telescope has opened a new window into the study of Giant Planets in the Solar System. During its first cycle, JWST observed Jupiter and its moons as part of the Early Release Science program ERS1373. JWST studied –Among its multiple observations – Jupiter using NIRCam imaging [1] together with NIRSpec and MIRI IFU modes [2–4], demonstrating JWST’s extraordinary capability to probe the stratospheric and thermospheric structure of the giant planet. However, these very first observations, specifically for MIRI, specifically aimed at the south polar region and only partially sampled the southern auroral oval itself, with only one observation directly probing the polar auroral region, interior of the main oval. 

A new observation campaign for Jupiter was carried out with JWST in February 2026, which overcame these coverage limitations. The main goal of this campaign was to  produce the most extensive and comprehensive dataset of Jupiter’s atmosphere obtained so far. This campaign combines observations from programs GO8173, and GO6865, providing a complete meridional coverage of the planet, and allowing systematic observations both inside and outside the northern auroral oval with the MIRI/MRS instrument. The southern auroral oval could not be directly observed, being only partially covered. However, the combined dataset offers a unique opportunity to directly compare auroral and non-auroral regions under similar observing conditions in both poles.

The new observations have been corrected using improved preprocessing techniques specifically developed for JWST/MIRI data. Desaturation routines now allow us to recover the spectroscopic information up to 20 μm, while maintaining reliable photometric calibration up to approximately 15.5 μm. In addition, a new flat-field correction algorithm has been implemented to mitigate spectral-shift artifacts that affect differently within the detector Field Of View. This work will present the full preprocessing pipeline and discuss the impact of these corrections on the quality of the acquired spectra. The cleaned spectra were then analyzed using a radiative transfer code coupled to an inversion algorithm that has already been tested in previous studies for Jupiter and Saturn’s atmospheres datasets [5].

Temperature fields were then retrieved using the CH4​ ν4​ emission band. This spectral region is particularly sensitive to the atmospheric layers around the 50 mbar up to the 1 μbar pressure level when observing bright auroral regions, enabling the study of Jupiter’s upper atmosphere in those cases. In regions with sufficient thermospheric sensitivity such as the auroral regions, simultaneous retrievals of temperature and homopause altitude were performed following the methodology described in [3,6]. From these analyses, we derived temperature profiles spanning pressures from approximately 30 mbar down to 0.01 mbar, and we explore different atmospheric scenarios to constrain the location and variability of the homopause in both polar regions. Our preliminary results reveal clear thermal contrasts between auroral and non-auroral regions, with enhanced temperatures and vertical structure variations inside the auroral ovals compared to the non-quiescent regions. The retrievals also suggest substantial differences in homopause altitude when comparing regions inside and outside the ovals, potentially linked to differences in auroral energy deposition and atmospheric circulation. These findings provide new constraints on the coupling between Jupiter’s thermosphere and stratosphere and highlight the strong dynamical influence of auroral processes on the polar atmosphere.

Once the temperature structure was obtained, we retrieved the abundances of several hydrocarbons, including C2​H2​, C2​H6​, and C6​H6​. Mapping the spatial distribution of these species in the polar regions is needed for interpreting the abundances of the exogenic molecules, since many of their spectral signatures overlap with these hydrocarbon emission features. The resulting abundance maps are compared with the meridional distributions predicted by photochemical models [7], allowing us to infer ion-neutral chemistry processes. Early analyses indicate localized enhancements and departures from purely photochemical expectations, particularly at high latitudes, supporting the presence of strong auroral chemical pathways.

A major scientific goal of this work is the study of the exogenic species CO2​, H2​O, and HCN, whose abundances can be strongly influenced by polar atmospheric processes and, more specifically, auroral activity [8, 9]. Constraining the spatial variability of these molecules in the polar regions is essential for identifying how the exogenous molecules in Jupiter’s atmosphere can evolve with time. In that line, we will present our future plans for retrieving exogenic species across the entire planet, with particular interest in the mapping of the polar regions [10]. We will compare the abundances of CO2​, H2​O, and HCN inside and outside the auroral ovals, produce polar maps of CO2​ and H2​O, and retrieve the full meridional distribution of HCN column densities. We aim to analyze these results alongside the spatial distribution of Jupiter’s stratospheric polar aerosols, providing a broader picture of the interaction between auroral activity, atmospheric chemistry, and aerosol formation in Jupiter’s upper atmosphere.

 

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