Structure of Jupiter's Great Red Spot and South Polar Domain from JWST/NIRSpec and Juno/JIRAM
Authors: Fletcher Leigh N. , Biagiotti Francesco , King Oliver R.T. , Roman Michael T. , Melin Henrik , Harkett Jake , de Pater Imke , Fouchet Thierry , Mura Alessandro , Grassi Davide , Piccioni Guiseppe , Wong Mike , Rodríguez-Ovalle Pablo , Irwin Patrick , Orton Glenn , Fry Pat , Bjoraker Gordy , Hueso Ricardo 
Published: July 2024

We present observations of Jupiter&#8217;s atmosphere using JWST&#8217;s NIRSpec (Jakobsen+2022, doi:10.1051/0004-6361/202142663) integral field unit (IFU) spectrometer acquired during the first year of scientific operations.&#160; Near-infrared spectroscopic mapping provides a key tool for studying giant planet clouds, hazes, and gaseous composition from the cloud-forming weather layer to the radiatively-controlled lower stratosphere.&#160; Spectrometers that span the 1-5 &#181;m range provide access to reflected sunlight inside and outside of strong methane bands; ionospheric emission from H3+; and deep thermal emission from an atmospheric &#8216;window&#8217; near 5 &#181;m (where gaseous absorption is relatively low).&#160; The superb spectral sensitivity, spectral resolution (R~2700), and uninterrupted spectral range of NIRSpec/IFU has provided an exquisite dataset for studying the 3D structure of Jupiter&#8217;s dynamic atmosphere, with sensitivity to wavelengths that have been previously inaccessible.&#160; In this presentation, we compare NIRSpec/IFU spectra to those acquired by the JIRAM instrument (2-5 &#181;m spectrometer) on NASA&#8217;s Juno spacecraft (Adriani+2017, doi:10.1007/s11214-014-0094-y), and look ahead to future Jupiter observations by the MAJIS instrument on JUICE (Poulet+2024, doi:10.1007/s11214-024-01057-2).JWST Observations:&#160; We used the NIRSpec/IFU instrument to acquire spatially-resolved spectral maps of Jupiter across a 3x3&#8221; field-of-view (FOV), using mosaicking to ensure wide spatial coverage.&#160; Two gratings were used at high spectral resolution (R~2700, G235H and G395H) to span the 1.8-5.3 &#181;m range.&#160; While the small NIRSpec FOV precludes global mapping of Jupiter, representative regions of the atmosphere can be explored by combining multiple datasets.&#160; As part of early-release science (ERS, PIs:&#160; de Pater &amp; Fouchet) programme 1373, six mosaic tiles were used to map the Great Red Spot on 2022-07-27 using both gratings; six G395H (2.8-5.3 &#181;m) tiles and three G235H tiles (1.8-3.2 &#181;m) were used to map Jupiter&#8217;s South Polar domain on 2022-12-27.&#160; Data were reduced and navigated using the JWST pipeline and custom Solar System processing (King+2023, doi:10.3847/2515-5172/ad045f), mitigating the effects of saturation in reflectivity peaks near ~2 &#181;m and strong thermal emission at 5 &#181;m by subdividing long integrations into shorter durations (known as groups).&#160; Emission features from H3+ and CH4 fluorescence were identified in the data (Melin+2024) and removed to enable fitting of the neutral atmosphere.Great Red Spot:&#160; JWST captured the GRS in July 2022 in a relatively quiescent state (Fig. 1), with fine tendrils of material (reddish in visible light) forming an anticlockwise spiral at the edge of the vortex, and cloud-free lanes of low reflectivity and bright thermal emission surrounding both the red anticyclone and the reflective aerosols of the GRS hollow.&#160; Intriguingly, reflectivity maps between 3.0 and 4.5 &#181;m (sounding upper-tropospheric aerosols) show a series of concentric ovals, forming lanes around the centre of the GRS, with the most reflective in the centre where wind speeds are lowest (and sometimes there is a counter-rotating cyclonic core).&#160; A combination of principal component analysis (PCA) and Gaussian Mixture Models (GMM) was used to identify self-similar NIRSpec spectra (Biagiotti+2024, doi:10.5194/egusphere-egu24-12950), forming clusters for subsequent spectral inversion with NEMESIS to derive aerosol properties and gaseous abundances.&#160; The clustering naturally identified the different spectra in the dark cloud-free regions; the whitish aerosols of the GRS hollow; and the red-orange aerosols of the GRS.&#160; A persistent cluster defines the edge or halo of the GRS, showing a spectrum that is distinct from the GRS interior.&#160; We repeated the same analysis on Juno/JIRAM spectra of the GRS acquired during Juno&#8217;s first perijove (2016-08-27, Grassi+2021, doi:10.1093/mnras/stab740), albeit with lower spectral resolution and coarser coverage of the JIRAM spectrometer.&#160; The same clusters were identified, and the same persistent halo.&#160; The halo may be associated with the mixture of red chromophores and the underlying background clouds. The clusters show considerable difference in the shape of the 2.6-2.8 &#181;m reflectivity peak, indicating the presence of different cloud and haze properties (compositions, particle sizes, altitude distributions, etc.) in the different clusters.&#160; Clusters closer to the GRS centre appear to have a distinct 2.7-&#181;m reflectivity peak that is spectrally broader with enhanced reflection out beyond 3.0 &#181;m.&#160; Inversions varying the properties of the upper haze, deeper clouds, and abundances of ammonia and phosphine will be presented to determine the origin of the concentric lanes within the GRS.&#160; Results will be compared to previous near-IR studies from Galileo/NIMS (Baines+2002, doi:10.1006/icar.2002.6901) and ground-based observations (Bjoraker+2018, doi:10.3847/1538-3881/aad186).Figure 1 Jupiter's Great Red Spot observed by NIRpec at three wavelengths:&#160; 2.7 &#181;m (reflection from deep clouds); 4.5 &#181;m (combined reflection and thermal emission); and 4.6 &#181;m (deep thermal emission).South Polar Domain:&#160; The December-2022 mosaic spans approximately 100o longitude (centred on ~20oW) and 50-90oS, with clearly-identifiable transitions in reflectivity and thermal emission associated with the edge of the South Polar Hood (SPH, 68oS graphic); a low-reflectivity band (62-68oS between prograde jets S5 and S6); and reflective bands between 50-60oS with numerous small cyclones and anticyclonic ovals between the S4 and S5 jets.&#160; Folded Filamentary Regions (FFRs) are observed in a band at the edge of the SPH (68-73oS, Rogers+2022, doi:10.1016/j.icarus.2021.114742), appearing dark at 5 &#181;m, but the spatial sampling of the NIRSpec/IFU spaxels is insufficient to resolve details of the edges of the circumpolar cyclones (CPCs).&#160; H3+ emission clearly traces the outline of the southern auroral oval.&#160; Zonal averages of the southern mosaic will be used to explore changes in aerosol properties and composition across the edge of the SPH.&#160; Juno/JIRAM acquired a high-resolution M-band map of Jupiter&#8217;s south polar domain 9 days earlier (2022-12-15, perijove 47), allowing us to explore the longevity of the features in this longitude range.&#160; The entire south polar domain is bright at 5 &#181;m (i.e., thinner clouds, despite the reflective small-particle hazes of the SPH), punctuated by the darker (cloudier) FFRs and CPCs.Acknowledgements:&#160; JIRAM is funded by ASI&#8211;INAF Agreement 2016-23-H.3-2023.