Mid Infrared analysis of Jupiter South Pole from JWST MIRI-MRS observations: Thermo-chemical disturbances caused by auroral activity

Jupiter’s Polar Regions host a very strong auroral activity. The Jovian auroras leave their imprint in the ultraviolet spectral region, but also in the Mid-Infrared, which suggests that they can influence the thermal structure by heating up not only the thermosphere, but also the stratosphere by particle precipitation. Some studies suggest that auroral activity also influences the atmospheric chemistry by enhancing or depleting some stratospheric hydrocarbons produced by photochemistry, as well as other components such as HCN. Some hypotheses link these variations with the presence of polar hazes at high latitudes on Jupiter.

JWST performed several observations of the Jovian System in 2022, most of them as part of the Early Release Science program 1373 (ERS-1373). One of these observations targeted the South Polar Region. On the 24^th of December 2022, two spectrometers on board JWST, NIRSPec and MIRI carried out this observation, covering the spectral range from 1 to 28 μm (with the wavelengths beyond 15 microns completely saturated). Along with this observation, another earlier one was performed on July 2022 (OBS-1022), as part of the commissioning program. This complementary observation only covered the ranges 4.9-5.8, 7.4-8.8 and 11.5-13.5 μm, since it aimed only at testing the pointing of the instrument.

Both of these observations allowed us to obtain sufficient spectral and spatial information to map stratospheric temperature and hydrocarbons abundances.

We will show a complete analysis of the 1022 dataset. Despite the limited spectral range, we were able to measure stratospheric temperatures at pressures between 10 and 0.1 mbar and map the homopause height. To do so, we first needed to retrieve the homopause height (which determines the methane vertical profile of Jupiter) by a simultaneous analysis of fourteen different models of the atmosphere. We found that the auroral oval leaves an imprint in the stratosphere, creating a warmer region where the auroral oval can be spotted in the UV and IR. The analysis also shows an upwards displacement of the homopause level in the auroral oval, in agreement with previous studies but with a much better spatial resolution. We were also able to retrieve 3D maps of acetylene VMR.

Along with this analysis, we will present preliminary results on MIRI 1373 observation. This observation covers the full spectral region from 5 to 28 μm and, hence, it has sufficient information to determine the abundances and distributions of other molecules, such as ammonia, phosphine, ethylene and ethane among others. We will also present processed NIRCam images from the polar region as a support for the spectral analysis.