Survey of H3+ and CH4 Emissions in Jupiter's Aurorae from Juno/JIRAM Observations

The Jovian InfraRed Auroral Mapper (JIRAM) aboard NASA’s Juno spacecraft has significantly advanced our understanding of Jupiter’s aurorae by providing infrared observations with unprecedented spatial resolution. These measurements reveal fine-scale structures associated with H₃⁺ emissions and enhanced CH₄ concentrations over the polar caps, offering new insights into the coupling between Jupiter’s magnetosphere, thermosphere, and ionosphere. Leveraging Juno’s elliptical polar trajectory, the JIRAM imager and spectrometer have conducted repeated close-range observations of Jupiter’s auroral regions throughout the mission. This unique vantage point enables investigation of the morphology and temporal evolution of H₃⁺ and CH₄ emissions, particularly in the less-studied southern hemisphere, which remains largely inaccessible to Earth-based instruments. Extending beyond earlier analyses of Juno’s first perijove (PJ), we examine JIRAM observations from PJ1 (27 August 2016) to PJ40 (25 February 2022), restricting our study to orbits that provide the most complete spectroscopic coverage of the auroral regions, thereby enabling large-scale quantitative analysis and inter-orbit comparison. We derive the temperature and column density of H₃⁺ in Jupiter's auroral regions in the 3.2–3.8 mm range to generate detailed distribution maps. These reveal significant variability in auroral emissions, including a longitudinal displacement of the southern aurora over time, also evident in JIRAM L-band (3.3–3.6 mm) imagery. We further find that 3.3-mm methane bright spots are primarily confined within the auroral oval, with occasional indications of emission extending beyond the main boundary. Together, these results highlight the dynamic nature of Jupiter’s infrared aurora, consistent with variable atmospheric response to time-varying magnetospheric forcing.

Acknowledgments:

The authors acknowledge the Agenzia Spaziale Italiana (ASI) for supporting of the JIRAM contribution to the Juno mission, including this work, under the ASI contract 2016-23-H.0.