Jupiter's polar stratosphere exhibits unique chemical and dynamical processes that shape its atmospheric composition and structure. This paper reviews observational constraints and modeling efforts aimed at understanding the complex interplay between chemistry, dynamics, and aerosol microphysics in Jupiter's high-latitude regions.

Hydrocarbon observations from various instruments (e.g. Voyager/IRIS, Cassini/CIRS, IRTF/TEXES, Juno/UVS, and JWST/MIRI) have revealed significant abundance enhancements and latitudinal variations of species like acetylene (C₂H₂), ethylene (C₂H₄), ethane (C₂H₆), methylacetylene (CH₃C₂H), and benzene (C₆H₆) within the auroral regions. These enhancements are attributed to the influence of auroral processes and possible enhanced vertical mixing. IRTF/TEXES and JWST/MIRI also provided insights into the vertical structure of the polar atmosphere, suggesting that the methane homopause (i.e. the altitude where the methane molecular diffusion coefficient equals the vertical eddy diffusion one, and above which CH₄ abundance decreases due to the molecular diffusion), is located at higher altitudes within the auroral regions compared to lower latitudes. Some of these observations also indicate that the aerosol layer is located at higher altitudes (above 20 mbar) in the polar regions compared to lower latitudes (around 50 mbar).

Modeling efforts have aimed to reproduce the observed meridional distributions of hydrocarbons and constrain the atmospheric dynamics and transport processes. 2D photochemical modeling, with parametrized meridional diffusion coefficients (Kyy) and advective circulation, suggests that a combination of moderate Kyy and a circulation cell with upwelling motions at the equator and downwelling motions at mid-latitudes is required to reproduce the observed meridional gradient of ethane (C₂H₆). Auroral chemistry models have explored the production of larger hydrocarbon ions and neutral species through ion-neutral reactions initiated by precipitating auroral particles, highlighting the potential role of auroral processes in the formation of stratospheric haze.

Cassini and ALMA observations of hydrogen cyanide (HCN) have revealed a striking enhancement and distinct vertical distribution within the auroral regions compared to lower latitudes, suggesting the influence of atmospheric dynamics on the chemical distributions. Measurements of the Doppler shifts in H₃⁺ emission lines from ground-based telescopes, combined with measurements of wind-induced Doppler shifted HCN lines from ALMA, have revealed the presence of strong upper-atmospheric winds circulating around Jupiter's polar regions, possibly influencing the circulation down to the middle stratosphere.

Recent observations and modeling efforts have advanced our understanding of Jupiter's polar stratosphere. Key findings include the enhancement of hydrocarbon abundances within auroral regions, the higher altitude of the methane homopause and aerosol layers in polar regions, and the interplay between chemistry, dynamics, and aerosol microphysics in shaping the atmospheric composition and structure. We summarize the remaining outstanding questions that are to be addressed by current as well as forthcoming facilities and space missions.

Figure 1: Summary schematics of selected chemical distributions across Jupiter’s polar region. Particle precipitation leads to the formation of H₃⁺ in the ionosphere, and to UV-auroras through the H and H₂ emissions at the μbar level. Around the μbar level and below, solar-UV photolysis as well as charged particle precipitation leads to the formation of hydrocarbons. As hydrocarbons diffuse downward, they combine into heavier hydrocarbons and eventually form aerosols. HCN produced in the upper atmosphere, possibly from N₂ destruction, becomes incorporated into aerosols before reaching ∼2mbar or below.

How to cite: Hue, V., Cavalié, T., Sinclair, J. A., Zhang, X., Benmahi, B., Rodríguez-Ovalle, P., Giles, R. S., Stallard, T. S., Johnson, R. E., Dobrijevic, M., Fouchet, T., Greathouse, T. K., Grodent, D. C., Hueso, R., Mousis, O., and Nixon, C. A.: The Polar Stratosphere of Jupiter, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-512, https://doi.org/10.5194/epsc2024-512, 2024.

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How to cite: Smirnova, M., Galanti, E., Caruso, A., Buccino, D., Gomez Casajus, L. A., Gramigna, E., Zannoni, M., Parisi, M., Hubbard, B., Steffes, P., Levin, S., Bolton, S., Tortora, P., and Kaspi, Y.: Analysis of Jupiter's atmosphere using Juno's radio occultations, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-866, https://doi.org/10.5194/epsc2024-866, 2024.

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Updated formation and structure models of Jupiter predict a metal-poor envelope. This is at odds with the two to three times solar metallicity measured by the Galileo probe. Additionally, Juno data imply that water and ammonia are enriched. This talk explores whether Jupiter can have a deep radiative layer separating the atmosphere from the deeper interior. The radiative layer could be caused by a hydrogen-transparency window or depletion of alkali metals.

We show that heavy-element accretion during Jupiter's evolution can lead to the desired atmospheric enrichment and that this configuration is stable over billions of years. The origin of the heavy elements could be cumulative small impacts or one large impact. The preferred scenario requires a deep radiative zone due to a local reduction of the opacity at ∼ 2000 K by ∼ 90%, which is supported by Juno data, and vertical mixing through the boundary with a similar efficiency to molecular diffusion (D ≤ 10^-2 cm²/s). Most of Jupiter's molecular envelope could have solar composition while its uppermost atmosphere is enriched with heavier elements. The enrichment likely originates from the accretion of solid objects.

This possibility resolves the long-standing mismatch between Jupiter's interior models and atmospheric composition measurements. Furthermore, our results imply that the measured atmospheric composition of exoplanets does not necessarily reflect their bulk compositions. We also investigate whether the enrichment could be due to the erosion of a dilute core and show that this is highly unlikely. The core-erosion scenario is inconsistent with evolution calculations, the deep radiative layer, and published interior models.

How to cite: Müller, S. and Helled, R.: Can Jupiter's atmospheric metallicity be different from the deep interior?, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-734, https://doi.org/10.5194/epsc2024-734, 2024.

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Jupiter’s upper atmosphere (thermosphere/ionosphere) forms the link between its deeper atmosphere and the vast magnetosphere with its current systems, some of which close in the planet’s auroral region. The combination of acceleration and heating have profound influence on the dynamics and temperatures of Jupiter’s upper atmosphere. The ongoing Juno and future JUICE missions as well as Earth based observations provide us with new measurements and questions about the upper atmosphere structure and dynamics. Fundamentally, the aim is to understand this highly coupled upper atmosphere region which is driven to varying degrees by the magnetosphere and by the deeper atmosphere via vertically propagating waves.

Exploring such a complex system requires global numerical models. Based on our Saturn Thermosphere Ionosphere Model (STIM) [1, 2, 3], we have developed a Jupiter Thermosphere Ionosphere Model (JTIM) which includes similar features as STIM, a thermosphere model coupled chemically and dynamically to an ionosphere model. The code numerically solves the coupled non-linear Navier Stokes equations of momentum, energy and continuity, including eddy and molecular diffusion of neutral gases and full two-way ion-neutral coupling. The magnetosphere interaction is currently accounted for by mapping a magnetospheric electric field and precipitation pattern into the polar regions and allowing for particle impact ionization in the auroral regions. The thermosphere’s lower boundary is flexible to allow for coupling to the deeper atmosphere via mean background parameters and atmospheric waves.

We present first simulations of the model with a focus on the complex thermosphere dynamics and thermal structure. The use of similar models for both Saturn and Jupiter allows for direct comparisons between the planets and difference in underlying physical processes under differing boundary conditions. We also address the question of the well-known upper atmosphere temperature conundrum which is common to all giant planets in our solar system.

References:

[1] Müller-Wodarg et al. A global circulation model of Saturn’s thermosphere. Icarus, 180, 2006.

[2] Müller-Wodarg et al. Magnetosphere-atmosphere coupling at Saturn: 1 – Response of thermosphere and ionosphere to steady state polar forcing. Icarus, 221, 2012.

[3] Müller-Wodarg et al. Atmospheric Waves and Their Possible Effect on the Thermal Structure of Saturn's Thermosphere. Geophysical Research Letters, 46, 2019.

How to cite: Müller-Wodarg, I., Iñurrigarro Rodriguez, P., Moore, L., Medvedev, A., and Koskinen, T.: Dynamics and thermal structure of Jupiter’s thermosphere in response to magnetosphere-atmosphere coupling, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-553, https://doi.org/10.5194/epsc2024-553, 2024.

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By combining data from JunoCam and ground-based images, we present a history of the large-scale cyclonic structures in Jupiter’s S2 domain spanning 7.5 years, thus establishing the range of lifetimes of chaotic formations for the first time. The S2 domain lies between the prograde jets at 36ºS (planetographic) and 43ºS, encompassing the traditionally named South South Temperate Belt (SSTB) and Zone (SSTZ).  The most distinctive features here are 6 to 9 long-lived anticyclonic white ovals (AWOs) [ref.1].  Between them are a number of cyclonic circulations, which have been well characterised by short-term imaging from previous spacecraft, but could not be comprehensively followed because many of them were not well resolved in ground-based images.  Images from JunoCam now enable most or all of them to be characterised on each of Juno’s orbits (e.g. Figure 1), and modern amateur imaging can resolve them more frequently for several months around Jupiter’s oppositions (e.g. Figure 2).  Thus we can now document these cyclonic features in the SSTB continuously from 2015 to 2023, along with high-resolution views of them from JunoCam.

They fall into three categories:  (i) Cyclonic dark spots or oblongs, often dark brown. (ii) Cylonic white oblongs (CWOs).  (iii) Folded filamentary regions (FFRs).

The first two are closed circulations; FFRs are more chaotic and may emit disturbance to east and west. The JunoCam images also sometimes reveal long, pale fawn-coloured sectors of the SSTB that resemble CWOs in structure and are probably closed circulations. In ground-based images these may appear as a dull-white CWO (because JunoCam is more sensitive to blue absorption than typical amateur filters) or as a nondescript sector of the SSTB. 

A diagrammatic chart showing the history of these types of cyclonic feature is in Figure 3.  Any of them can last for as little as ~4 months.  CWOs often last longer, ranging up to 2.8 years in this survey, and up to nearly 6 years in earlier ground-based records [ref.1].  FFRs also have a large range of lifetimes, although they may sometimes be temporarily weak; two have existed for the full duration of this survey (>7.5 years). Some sectors (delimited by AWOs) have shown repeated changes between the cyclonic types: any of three types can convert into any other over a matter of months, sometimes via a pale ochre oblong as intermediate (Figures 1 & 4).

Dark oblongs may form when a FFR becomes inactive.  Dark spots or oblongs often end their lives by becoming redder and then lighter in colour, sometimes becoming white.  Some of these dark spots are very small and can turn into white ovals that do not expand; these are not considered further here.  Longer structures can turn into light oblongs which expand in longitude as CWOs. 

CWOs sometimes brighten rapidly in their early stages; a new one in 2018 was very bright white and also bright in the 889-nm methane band, as was one in 2013 (just before this survey period).  This was not a transient convective plume, but static methane-brightness of the white oblong, which is a very rare condition for a cyclonic oval on Jupiter.  CWOs always expand in longitude during their lifetime. Four CWOs whose later stages were observed by JunoCam all ended gradually, changing from white to dull white or fawn, sometimes being very long but retaining the loop form suggesting continuing circulation; sometimes it was also visibly disturbed.  This stage lasted for up to a year; then in three cases it was terminated by a new FFR developing within its former boundaries.

New FFRs have appeared and disappeared about once a year.  A young FFR is usually small and expands, though they do not grow indefinitely.  We have never noted an especially bright convective outbreak initiating a FFR, though many could have gone undetected; and only one JunoCam observation of a young one showed it as methane-bright.

All three types are equivalent to cyclonic features in most other domains, although their relative size and importance vary. [See our abstract in the ODAA1 session for the STB.]  For example, dark spots or oblongs are smaller versions of ‘barges’ in the NEB; CWOs resemble structures in the STB; and FFRs are increasingly dominant in higher-latitude domains. This study is the first to show the full timecourse of FFRs.  Similar studies will be possible for other domains, in which the FFRs may be more variable and perhaps shorter-lived because they are not usually confined by AWOs.

Acknowledgements:  Some of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004).

Details of the observations are posted in our regular reports on the JunoCam and BAA websites: 

https://www.missionjuno.swri.edu/junocam;  https://britastro.org/sections/jupiter

Reference 1:  Rogers J, Adamoli G, Hahn G, Jacquesson M, Vedovato M, & Mettig H-J (2014).  ‘Jupiter’s southern high-latitude domains: long-lived features and dynamics, 2001-2012.’ http://www.britastro.org/jupiter/sstemp2014.htm

Figure 1:

Figure 2:

Figure 3:

Figure 4:

How to cite: Rogers, J., Hansen, C., Eichstädt, G., Orton, G., Momary, T., Adamoli, G., Bullen, R., Jacquesson, M., Vedovato, M., and Mettig, H.-J.: Longevity of cyclonic formations in Jupiter’s S2 (South South Temperate) Domain, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-378, https://doi.org/10.5194/epsc2024-378, 2024.

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Introduction

Storms on Earth barely develop counter-rotating cores nor do so computer simulations of two-dimensional and incompressible Euler fluids [2]. But on Jupiter, JunoCam [1], the visible light imager on NASA's Juno spacecraft, collected image data of northern circumpolar cyclones (CPCs) that show distinct counter-rotating cores. Those cores occur either frequently, or they are often stable over several months.

The data points of our long-term time series are separated by the duration of at least one Juno orbit. Short-term image sequences taken during each of the considered Jupiter flybys reveal the morphology as well as the dynamics of a CPC.

While color images provide sufficient detail to measure angular velocities by stereo correspondence, and to derive vorticity maps, some of the methane-band image sequences reveal that counter-rotating cores do not stand out significantly. Two layers of clouds, one with a converging cyclonic flow, and one with a diverging anticyclonic flow, are not immediatley suggested by methane-band images. Therefore, a fluid-dynamical solution of counter-rotation within a two dimensional geometry ought to be found.

A counter-rotating core in a vortex of a two-dimensional Euler fluid is unstable. It is either ejected or disrupted in many cases.

Modelling a second layer, one with a steady flow, and allowing for some friction with the two-dimensional fluid of interest, can stabilize the counter-rotating core. The friction acts equivalently to vortex flux into or out of the layer of interest. The vortex flux is defined to be proportional to the difference between the vorticity fields of the two fluid layers, while the reference vorticity field remains constant. The global parameter of proportionality can be varied between 0 and 1, where 0 means no effect to the two-dimensional Euler fluid, and 1 means an identical copy of the steady flow. It's convenient to define the parameter of proportionality in terms the half-life of the vorticity flux in a sense that after that time, half of the vorticity difference would be leveled out in the absence of dynamics. A half-life of infinity translates into a parameter of proportionality of 0 for each simulation step, and a half-life of 0 translates into a parameter of proportionality of 1.

Vorticity maps and radial vorticity profiles in JunoCam images of CPCs

Figure 1

The first column of Figure 1 shows a northern CPC without a counter-rotating core. The angular velocity is increasing with decreasing distance from its center. The morphology shows a  typical spiral structure, the vorticity map shows a strongly cyclonic core, and the radial vorticity profile (blue line in the diagram) has its cyclonic maximum at the center of the cyclone (left end of the x-axis).

The two other columns show two CPCs with counter-rotating cores. The central column shows a gradual transition from cyclonic to anticyclonic rotation with decreasing radius, while the right colums shows a sharp boundary between the anticyclonic core and its cyclonic environment. In both cases, the radial vorticity profile shows an anticyclonic maximum at the center of the cyclone and a shallow local cyclonic maximum outside the center of the cyclone.

While an anticyclonic morphology can form for a cyclone with cyclonic vorticity decreasing towards the center, measurements of the dynamics return distinct anticyclonic rotation in the cores.

Long-term stability of anticyclonic cores

Figure 2

JunoCam observes the same CPC during several Jupiter flybys. Figure 2 shows such an example. The same CPC was observed during the PJ50, PJ51, PJ54, and PJ58 flybys. Each time, an anticyclonic morphology was detected at the core of the CPC. This means either that such a morphology developed with each flyby, or, more plausibly, lasted at least from PJ50 (2023 APR 08) to PJ58 (2024 FEB 03), hence for about ten months.

Methane-band images hint towards 2D embedding of the counter-rotation

Figure 3

The left column of Figure 3 shows a CPC with a cyclonic core, while the right column shows an example with a counter-rotating core. In both cases, color and methane-band images are available. The methane-band images do not show a significant difference between the relative elevation profiles of the two cyclones. With the cyclonic core assumed to be embedded in a 2D flow, this suggests that the same should be considered for the anticyclonic core.

Counter-rotating cores are unstable in an incompressible 2D Euler flow

Figure 4

Counter-rotating cores in an incompressible 2D Euler flow are usually either ejected or disrupted. Figure 4 visualizes time series of both scenarios. Bluish symbolizes cyclonic vorticity, and yellowish anticyclonic vorticity.

Vorticity flux by friction with a second layer stabilizes counter-rotation

Figure 5

Each row in Figure 5 represents a time series of the same 2D flow, but with varying levels of friction with a steady flow identical to the left-most column of the survey. The half-life of the vorticity flux increases from top to bottom. The top line approximates a steady flow with a stable counter-rotating core rather quickly, while the bottom line represents just the 2D Euler fluid without friction.

Conclusion

The counter-rotating core observed in Jupiter's northern CPCs suggest to exist in an approximately 2D fluid dynamical settings. Such a flow appears to be unstable for an incompressible 2D Euler flow. But for an appropriate vorticity exchange with a steady flow in a second 2D layer, the incompressible 2D Euler flow can be extended to a vortex with a stable counter-rotating core. The cause of the assumed steady flow in the second fluid level is out of the scope of this article.

Acknowledgement

Some of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004).

References

[1] C.J. Hansen, M.A. Caplinger, A. Ingersoll, M.A. Ravine, E. Jensen, S. Bolton, G. Orton. Junocam: Juno’s Outreach Camera. Space Sci Rev 2013:475-506, 2017

[2] Eichstädt, G., Hansen, C., and Orton, G.: Fluid Dynamical 2D Simulations of Jupiter's South Polar Region Based On JunoCam Image Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12025, https://doi.org/10.5194/egusphere-egu2020-12025, 2020.

How to cite: Eichstädt, G., Brueshaber, S., Li, C., Orton, G., Rogers, J., Hansen-Koharcheck, C., and Bolton, S.: Counter-rotating cores in Jupiter's circum-polar cyclones observed by JunoCam and modeled in 2D, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-154, https://doi.org/10.5194/epsc2024-154, 2024.

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Whistler-mode chorus waves are frequently observed in the Jovian magnetosphere and are known to play an important role in the dynamics of radiation belt electrons. By combining the observations from Galileo and Juno, we conducted a detailed statistical analysis of the spatial distribution of the occurrence rates, power spectral densities and averaged amplitudes of chorus waves in the Jovian magnetosphere. The statistical results show that chorus waves are mainly distributed in the near-equatorial (<20°) region at 5< M-shell <12. The averaged wave amplitudes range from several pT to tens of pT and are significantly enhanced in the vicinity of Europa and Ganymede. The wave amplitudes peak at M-shell = 8-11 within λ≤10° with a strong dawn-dusk asymmetry. In addition, the wave power spectral intensities decrease monotonically with increasing f/f_ce, where f and f_ce are the wave frequency and electron gyrofrequency, respectively. We subsequently construct an empirical model of the distribution of chorus wave amplitudes with M-shell, magnetic latitude and magnetic local time. Based on the developed wave model, we investigate the resonant interactions between chorus wave and radiation belt electrons at different M-shells. Our results improve the current understanding of the statistical distribution properties of chorus waves and their role in the dynamics of radiation belt electrons at Jupiter.

How to cite: Cao, X., Lu, P., Ni, B., and Wang, S.: Statistical distribution of chorus waves in the Jovian magnetosphere and their resonant interactions with radiation belt electrons, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-689, https://doi.org/10.5194/epsc2024-689, 2024.

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We present observations of Jupiter’s atmosphere using JWST’s NIRSpec (Jakobsen+2022, doi:10.1051/0004-6361/202142663) integral field unit (IFU) spectrometer acquired during the first year of scientific operations.  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.  Spectrometers that span the 1-5 µm range provide access to reflected sunlight inside and outside of strong methane bands; ionospheric emission from H3+; and deep thermal emission from an atmospheric ‘window’ near 5 µm (where gaseous absorption is relatively low).  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’s dynamic atmosphere, with sensitivity to wavelengths that have been previously inaccessible.  In this presentation, we compare NIRSpec/IFU spectra to those acquired by the JIRAM instrument (2-5 µm spectrometer) on NASA’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:  We used the NIRSpec/IFU instrument to acquire spatially-resolved spectral maps of Jupiter across a 3x3” field-of-view (FOV), using mosaicking to ensure wide spatial coverage.  Two gratings were used at high spectral resolution (R~2700, G235H and G395H) to span the 1.8-5.3 µm range.  While the small NIRSpec FOV precludes global mapping of Jupiter, representative regions of the atmosphere can be explored by combining multiple datasets.  As part of early-release science (ERS, PIs:  de Pater & 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 µm) tiles and three G235H tiles (1.8-3.2 µm) were used to map Jupiter’s South Polar domain on 2022-12-27.  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 µm and strong thermal emission at 5 µm by subdividing long integrations into shorter durations (known as groups).  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:  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.  Intriguingly, reflectivity maps between 3.0 and 4.5 µm (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).  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.  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.  A persistent cluster defines the edge or halo of the GRS, showing a spectrum that is distinct from the GRS interior.  We repeated the same analysis on Juno/JIRAM spectra of the GRS acquired during Juno’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.  The same clusters were identified, and the same persistent halo.  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 µm reflectivity peak, indicating the presence of different cloud and haze properties (compositions, particle sizes, altitude distributions, etc.) in the different clusters.  Clusters closer to the GRS centre appear to have a distinct 2.7-µm reflectivity peak that is spectrally broader with enhanced reflection out beyond 3.0 µm.  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.  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:  2.7 µm (reflection from deep clouds); 4.5 µm (combined reflection and thermal emission); and 4.6 µm (deep thermal emission).

South Polar Domain:  The December-2022 mosaic spans approximately 100^o longitude (centred on ~20^oW) and 50-90^oS, with clearly-identifiable transitions in reflectivity and thermal emission associated with the edge of the South Polar Hood (SPH, 68^oS graphic); a low-reflectivity band (62-68^oS between prograde jets S5 and S6); and reflective bands between 50-60^oS with numerous small cyclones and anticyclonic ovals between the S4 and S5 jets.  Folded Filamentary Regions (FFRs) are observed in a band at the edge of the SPH (68-73^oS, Rogers+2022, doi:10.1016/j.icarus.2021.114742), appearing dark at 5 µm, but the spatial sampling of the NIRSpec/IFU spaxels is insufficient to resolve details of the edges of the circumpolar cyclones (CPCs).  H₃⁺ emission clearly traces the outline of the southern auroral oval.  Zonal averages of the southern mosaic will be used to explore changes in aerosol properties and composition across the edge of the SPH.  Juno/JIRAM acquired a high-resolution M-band map of Jupiter’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.  The entire south polar domain is bright at 5 µm (i.e., thinner clouds, despite the reflective small-particle hazes of the SPH), punctuated by the darker (cloudier) FFRs and CPCs.

Acknowledgements:  JIRAM is funded by ASI–INAF Agreement 2016-23-H.3-2023.

How to cite: Fletcher, L. N., Biagiotti, F., King, O. R. T., Roman, M. T., Melin, H., Harkett, J., de Pater, I., Fouchet, T., Mura, A., Grassi, D., Piccioni, G., Wong, M., Rodríguez-Ovalle, P., Irwin, P., Orton, G., Fry, P., Bjoraker, G., and Hueso, R.: Structure of Jupiter's Great Red Spot and South Polar Domain from JWST/NIRSpec and Juno/JIRAM, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-801, https://doi.org/10.5194/epsc2024-801, 2024.

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The Juno Microwave Radiometer (MWR) has been collecting data in the Jovian system since 2016.  MWR has 6 independent channels, at frequencies of 0.6, 1.2, 2.5, 4.8, 9.6, and 22 GHz, with bandwidths ranging from 3.2% to 3.5% (Janssen et al.  2016).  The angular resolution of the 0.6 and 1.2 GHz channels is roughly 21˚ and the other channels have about 11˚ beamwidth.  The two low-frequency channels have high- and low-gain outputs, to accommodate the dynamic range needed for observations of the Jovian synchrotron emission.  The absolute gain is calibrated to roughly 1%, but is very stable over hours-long time scales, so that the uncertainty in difference measurements is less than 0.2%, a fact which is very important for optimal use of the data (Zhang et al. 2020).  The antenna patterns are well characterized, and the trajectory, spacecraft orientation, and spin typically enable differential limb-darkening measurements of the atmosphere with brightness temperature estimates that deconvolve the antenna gain for better effective angular resolution (Oyafuso et al. 2020).  Lower frequencies penetrate to greater depths, and MWR’s 6 channels cover three orders of magnitude from deepest to shallowest contribution function, with the 600-MHz channel achieving passive measurements of the temperature and opacity at hundreds of km into Jupiter’s atmosphere, or several km into the ice shells of Ganymede and Europa.

MWR has produced a remarkable series of discoveries.  Measurements of the atmosphere have yielded conclusions about Jupiter’s temperature and composition vs depth and latitude (e.g. Li et al. 2024), Ferrel-like circulation cells (Duer et al. 2021), 3-dimensional characterization of atmospheric storms (Bolton et al. 2021), multi-year variability of large-scale features at depth, nature of the circumpolar cyclones, prevalence and distribution of lightning (Brown et al. 2018), depletion of alkali metals (Bhattacharya et al. 2023), time-varying free electrons over the northern aurora, and more.  Measurements of Ganymede (Brown et al. 2023, Zhang et al. 2023) and Europa have given insight into their subsurface ice, while observations of Io tell us about its rocky surface and lava below. MWR observations of synchrotron emission give us an unprecedented view of the inner radiation belts.   We will present an overview of MWR results to date, with an emphasis on the most recent discoveries and how the MWR data are used to achieve them.

References

Bhattacharya, A. et al. 2023.  ApJL, 952:L27.

Bolton, S. et al. 2021.  Science, 374, 968–972.

Brown, S. et al. 2018.  Nature, 558, 87.

Brown, S. et al. 2023.  JGR Planets, 128, Issue 6.

Duer, K. et al. 2021.  GRL, 48 (23), e2021GL095651

Janssen, M. et al. 2017. Space Sci. Rev. 213, 139.

Li, C. et al. 2024.  Icarus, 414, 116028.

Oyafuso, F. et al. 2020. Earth and Space Science,7, e2020EA001254.

Zhang, Z. et al. 2020.  Earth and Space Science,7, e2020EA001229.

Zhang, Z. et al. 2023.  GRL,50, e2022GL101565.

How to cite: Levin, S. and the Juno MWR Team: Juno Microwave Radiometer Results From 8 Years At Jupiter, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-674, https://doi.org/10.5194/epsc2024-674, 2024.

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Introduction

This is a preliminary report on measurements by Juno’s Microwave Radiometer (MWR) of cyclonic vortices in Jupiter’s north polar region. Juno discovered cyclones close to both rotational poles, surrounded by constellations of circumpolar cyclones (CPCs) ~7° from the poles with diameters of ~4000-6000 km (Orton et al. 2017, Adriani et al. 2018). The CPCs move very slowly in longitudes fixed to the interior (System-III) and are stable in their general morphology (‘filled’ vs ‘chaotic’ or ‘spiral’) in the visible or at 5 µm (Tabataba-Vakili et al. 2020, Adriani et al. 2020, Mura et al. 2022). Mura et al. (2021, 2022) noted that the longevity and stability of the CPCs raises questions about their depth. Models range from shallow-water (Li et al. 2020) to deep convection (e.g. Yadav et al. 2020, Garcia et al. 2020, Cai et al. 2021). Credible 3D models require knowledge of their properties at depth.

MWR Observations

MWR observations, 1.38 - 50 cm in wavelength (Janssen et al. 2017), sense Jupiter at pressures of 0.7 to over 100 bars (Figure 1). Only recently could the MWR resolve the northern CPCs and North Polar Cyclone (NPC), enabled by successive close approaches (“perijoves” or PJs) migrating northward, shortening the distance between the spacecraft and the north polar region. The CPCs are all recognizable in Ch. 6, as relatively bright, with CPCs 2, 6 and 8 much dimmer than the others (Fig. 2). Unlike the CPCs, the NPC has one of the coldest antenna temperatures in the region. 

  Figure 3 shows that CPCs 1, 3, 4, 5 and 7 are detectable in Ch. 4-6. CPCs 2, 6 and 8 are undetectable in Ch. 3-5. CPCs 3, 5, and 7 are detectable in Ch. 3. A feature associated with CPC 1 could be present but is indistinguishable from a broad, warm background region.  The North Polar Cyclone has a relatively colder antenna temperature in all channels.

Discussion

The MWR maps are remarkable.  The chaotic or spiral CPCs (2, 6 and 8) are faint, smaller and closer to the rotational pole than the filled CPCs 1, 3, 5 and 7. The strength of all the cyclones (positive for the CPCs and negative for the NPC) diminish with depth. The virtual disappearance of chaotic/spiral CPCs 2, 6 and 8 in channels sensitive to pressures of 1.5 – 3 bars implies that they are probably shallower than the prominent, filled CPCs.  The appearance of CPCs in Ch. 3 means they have roots down to at least 9 bars of pressure. MWR observations of a cyclonic vortex at 38°N (Bolton et al. 2021) showed a similar behavior, but its brightness temperature ‘signature’ changed from positive to negative in Ch. 3, implying an inversion around 3-6 bars. An inversion is not evident here for either chaotic/spiral CPCs or the filled CPCs, except possibly for CPC4. Bolton et al. (2021) noted that if the warm brightness temperature is the result of a lower NH₃ abundance, a dynamical mechanism is needed to transport ammonia downward from the upper atmospheric layers. A similar mechanism may be responsible for the northern CPCs, with the diversity of their strengths and depth dependences governed by a range of cyclonic vorticities. The cold NPC remains the most puzzling, as it is more similar to anticyclones, e.g. the Great Red Spot and an anticyclone at 19°N (Bolton et al. 2021), requiring higher NH₃ abundances or colder temperatures. Separating physical temperatures and NH₃ opacity is possible using observations resolving the cyclones over a range of emission angles, an approach successfully used for Jupiter’s equator (Li et al. 2024). We will take advantage of this using MWR measurements of this region at increasing spatial resolution between now and the expected mission end in late 2025.

Some of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004).

Figure 1. Contribution functions of MWR channels. Measurements from Ch. 1 and 2, were not used in this study; their fields of view are twice as large as Ch. 3-6, and they did not resolve the CPCs sufficiently.

Figure 2. The morphologies of the region northward of 78° planetocentric latitude from three Juno instruments. Longitudes are 0° at the bottom and increase clockwise. The MWR map shows composite antenna temperatures for Ch. 6 PJ52-PJ60. The MWR fields of view are about the same size as the CPCs shown at higher resolution by JunoCam and JIRAM. The JunoCam map combines PJ57 and PJ58, and the 5-µm JIRAM map is the last contiguous one of this region. The North Polar Cyclone (“NPC”) and numerical CPC labels are shown in the JunoCam panel. The locations of the CPCs are very similar in each of the maps, due to their very slow longitudinal motion in System III.

Figure 3.  MWR maps of antenna temperature from PJ60 observations in Ch. 3-6 with the same orientation as in Fig. 2, together with the pressure of the contribution function maximum of each channel (see Fig. 1).  The fields of view of these channels are the same. Numerical identifications of the CPCs are shown. The keys give the respective range of antenna temperature values for each channel.

References

Adriani, A. et al. 2018. Nature 555, 216.

Adriani, A. et al. 2020. J. Geophys. Res. Planets 125, e2019JE006098.

Bolton et al. 2021. Science 374, 968.

Cai, T. et al. 2021. Planet. Sci. J. 2, 81.

Janssen, M. et al. 2017. Space Sci. Rev. 213, 139.

Garcia, F. et al. 2020. Mon. Not. Roy. Astron. Soc. 499, 4698.

Gavriel, N. & Kaspi, Y, 2021. Nature Geosci. 14, 559.

Li, C. et al. 2020. Proc. Nat. Acad. Sci USA 117, 24082.

Li, C. et al. 2024.  Icarus 414, 116028 (15 pp).

Mura, A. et al. 2021. Geophys. Res. Lett. 481, 32021GL094235.

Mura, A. et al. 2022. J. Geophys. Res. Planets 127, e2022JJE007241.

Orton, G. S. et al. 2017. Geophys. Res. Lett. 44, 4599.

Tabataba-Vakili, F. et al. 2020. Icarus 335, 113405.

Yadav, R. K. et al. 2020. Sci. Adv. 6, eabb9298.

How to cite: Orton, G., Brown, S., Brueshaber, S., Li, C., Levin, S., Ingersoll, A., Zhang, Z., Rogers, J., Eichstaedt, G., Bolton, S., Momary, T., Hansen, C., Fletcher, L., and Mura, A.: Unexpected Results from Microwave Sounding of Jupiter’s North Polar Cyclones, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-280, https://doi.org/10.5194/epsc2024-280, 2024.

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 Jupiter’s atmosphere is primarily composed of molecular hydrogen and helium.

Since the atmosphere of this gaseous giant represents a high-density environment, the H₂ Collision Induced Absorption (CIA) fundamental band represents one of the main sources of opacity in the infrared part of the spectrum, particularly between 1 and 5 μm, which is a spectral range widely used by remote sensing instruments.

For this reason, it is important to have experimental data on the CIA absorption and to compare them with the theoretical models present in the literature, to have an estimation as accurate as possible of Jupiter’s atmospheric opacity, which represents important information for the already deployed Juno and Juice missions.

Consequently, measurements of the hydrogen CIA fundamental band have been performed in a wide range of temperature and pressure conditions, including the Jovian upper-tropospheric ones.

We performed measurements using a pure H₂ gas and an H₂-He mixture at typical Jovian concentrations (13.6% of He) and for different mixing ratios.

We used an experimental setup called PASSxS (Planetary Atmosphere Simulation for Spectroscopy) [1], which allows us to record spectra in the spectral range from 1 to 5 μm.

It comprises two stainless steel concentric vessels, as shown in Figure 1. The inner one contains the gaseous mixture under investigation, while the external can be evacuated to ensure thermal insulation of the sample chamber from the external environment.

Moreover, the inner vessel contains a multipass cell coupled with an FT-IR spectrometer. It has been aligned to reach an optical path of 3.27 m. The spectral resolution of the FT-IR ranges from  0.06 to 10 cm^-1. For a more detailed description of the experimental setup refer to [1].

Figure 1: a graphical sketch of the PASSxS

Thanks to this experimental setup we obtained some high signal-to-noise ratio measurements in a temperature range that goes from 120K to 500K. Figure 2 shows the experimental binary absorption coefficients for a pure H₂ gas in this temperature range. These are the first experimental measurements of the CIA H₂ fundamental band at temperatures higher than 300K.

Figure 2: Pure H₂ binary absorption coefficients in the [120, 500] K temperature range

Moreover, we studied the H₂ CIA fundamental band for an H₂-He mixture for various He concentrations, from a minimum of 13.6% of He (Jovian concentration) to a maximum of 90% of He. Figure 3 shows the absorption coefficients obtained for the mixture of interest with a He concentration that goes from 0% (pure H₂ case) to 70% at room temperature. The measurements have been taken by inserting an initial H₂ pressure of 6 bar, and different He pressures.

As you can see, as the He concentration increases, the peak around 4200 cm^-1 becomes more pronounced.

Figure 3: Experimental absorption coefficients at room temperature for an H₂-He mixture at different He concentrations, for an initial H₂ pressure of 6 bar

Starting from the measurements acquired with the H₂-He mixture at a certain temperature, it is also possible to separate the contributions to the total absorption coefficients due to the H₂-H₂ and the H₂-He collisions, which are shown in Figure 4.

This allows us to re-calculate the absorption coefficients for any mixing ratio, and possibly study the opacity in this spectral range of any gaseous planet whose atmosphere is predominantly made of H₂ and He.

Figure 4: Absorption coefficients at room temperature for the H₂-H₂ (blue curve) and H₂-He (green curve) contributions. The red curves represent Abel's theoretical models [3]

Furthermore, using the typical Jovian He concentration we also performed measurements at three pressure and temperature conditions, chosen along Jupiter’s atmospheric profile shown in Figure 5. The three dots superimposed on the curve represent the chosen set points.

Figure 5: Jovian atmospheric profile [2]

Figure 6 shows the experimental absorption coefficients (blue curve) acquired for an H₂-He mixture for typical Jovian concentrations at 402 K and a pressure of 19.2 bar.

The band shows a maximum absorption around 4200 cm^-1 where the absorption coefficients reach a value of almost 5.8 10^-4 cm^-1.

Furthermore, the experimental data have been compared with Abel’s theoretical model [3] shown as the red curve. As one can see, there are some discrepancies between the data and the model, which should be investigated further.

Figure 6: Experimental absorption coefficients (blue curve) at typical Jupiter's upper-tropospheric conditions. The red curve represents Abel’s theoretical model [3]

Looking at the left side of the main peak of the band shown in Figure 6, it is easy to notice the presence of some tiny features called interference dips [4] not reproduced by the theoretical model.

They have been studied by acquiring some high-resolution spectra for a pure H₂ gas and an H₂-He mixture at room temperature for different pressure conditions.

The interference dips represent a lack of absorption at specific wavelengths.

We managed to resolve all four interference dips observed at the following wavenumbers: 4126 cm^-1, 4143 cm^-1, 4155 cm^-1 and 4161 cm^-1.

Acknowledgments: This work has been developed under the ASI-INAF agreement n. 2023-6-HH.0.

References:

[1] M. Snels and al. (2021), AMT 14, 7187–7197, https://doi.org/10.5194/amt-14-7187-2021.

[2] A. Seiff (1997),  Science Vol 276, pp.102-104,https://www.science.org/doi/10.1126/science.276.5309.102.

[3] M. Abel et al., (2012), The Journal of Chemical Physics, 136,https://doi.org/10.1063/1.3676405

[4] J. Van Kranendonk (1968), Canadian Journal of Physics Vol. 46, N. 10, https://doi.org/10.1139/p68-150.

How to cite: Vitali, F., Stefani, S., Piccioni, G., Grassi, D., and Snels, M.: Experimental results on the H2-H2 and H2-He collisional-induced absorption coefficients at typical Jupiter’s upper tropospheric conditions.  , Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-775, https://doi.org/10.5194/epsc2024-775, 2024.

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How to cite: Markham, S. and Guillot, T.: Stable stratification of the helium rain layer yields vastly different interiors and magnetic fields for Jupiter and Saturn, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-950, https://doi.org/10.5194/epsc2024-950, 2024.

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Gravity measurements of the gas giants, as well as ring seismology in the case of Saturn, have led to increasingly complex structure models for both planets. The latest interior models for Jupiter and Saturn include a dilute, diffuse, or fuzzy core at their centres (e.g., Mankovich & Fuller 2021; Militzer et al. 2022). However, the dynamical nature of this central region and its effects on the dynamo process are not well constrained. Some hypothesise that the deep interior takes the form of a fully stably stratified dilute core while others argue for a convecting (inner) dilute core and a stably stratified transitional envelope atop. Either of these models will act to alter the geometry of the convective dynamo region considerably, especially in combination with likely additional stably stratified layers at mid-depths, due to helium rain.

Here we use 3D numerical MHD simulations to explore the effect of a dilute-core dynamo. As a first step, we adopt an imposed axial dipole with varying strength as a proxy for a deep dilute-core dynamo. We investigate its effects on the dynamical flows and magnetic field generation process in the convective metallic hydrogen layer above. In addition, a stably stratified transitional layer between the dilute-core dynamo and the convective metallic hydrogen layer has been implemented in our numerical models. 

With these numerical simulations, we aim to elucidate 1) which type of structures models leads to Jupiter-like or Saturn-like surface magnetic fields, and 2) if the deep dilute-core dynamo will leave observable imprints in the spatial or temporal pattern of the magnetic field. 

How to cite: Wulff, P., Cao, H., and Aurnou, J.: The Effects of Nested Dynamos in the Gas Giants, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-688, https://doi.org/10.5194/epsc2024-688, 2024.

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How to cite: Nettelmann, N. and Fortney, J.: The disappearance of Jupiter's dilute core in favor of helium, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-73, https://doi.org/10.5194/epsc2024-73, 2024.

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How to cite: Moirano, A., Bonfond, B., Mura, A., Hue, V., Caruso, A., Benmahi, B., Grodent, D., Head, L. A., Gérard, J.-C., Sicorello, G., Greathouse, T. K., Gomez Casajus, L., Tortora, P., and Zannoni, M. and the JIRAM team: Moon-induced infrared and ultraviolet auroral emission at Jupiter: overview during the Juno mission, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-593, https://doi.org/10.5194/epsc2024-593, 2024.

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The Jovian magnetosphere, the largest in the Solar System, extends up to 50-100 Jovian radii. Io, Jupiter's innermost Galilean moon, orbits deep within this magnetosphere. Io’s volcanic activity emits 1 ton per second of material into the magnetosphere mainly SO₂. Collisions with magnetospheric particles ionize SO2, forming a torus-shaped plasma cloud called the Io Plasma Torus (IPT) around Jupiter. When Io moves through Jupiter’s magnetic field, Alfvén waves are generated that propagate along Jupiter's magnetic field lines, leading to Alfvén Wings that extend from Io toward Jupiter's poles.

In the past few years, Juno’s radio science instrumentation, which can transmit dual-frequency X-band (8.4 GHz) and Ka-band (32 GHz) radio signals, has been used to conduct radio occultation experiments for the measurements of the ionospheric plasma surrounding Jupiter and its moons, Ganymede and Europa. Recently, the spacecraft performed two close flybys of Io on December 29, 2023 and February 4, 2024, namely I57 and I58. During both encounters, the radio ray path traveled through the Alfvén wings that connect Io to Jupiter. On both Io’s flybys, the downlink plasma was extracted using the dual-link single-uplink multifrequency calibration. Indeed, by performing a linear combination of the X and Ka-band data collected at the Earth’s antenna (namely, the differential frequency depicted in Figure 1), we can directly extract the dispersive contribution to the Doppler shift in the downlink. The extracted Doppler shift induced by the dispersive media indicated a high electron concentration within the Alfvén wings.

Figure 1 Downlink plasma obtained by a linear combination of X and Ka-band data collected during the Io's flybys I57 and I58

These data provide information on the path delay of the signal and, consequently, the Total Electron Content along the line of sight. In order to retrieve the electron density inside these structures from the Doppler measurements, we must introduce some geometrical assumptions on the Alfvén wing's size, orientation, and electron density distribution. Due to their tubular shape, conventional radio occultation inversion methods cannot be used to perform this analysis. Consequently, for these experiments we developed novel techniques tailored to this particular case. We modified an existing ray-tracing-based inversion algorithm, used in the past for the analysis of spherical and oblate ionospheres, by adding the assumption of a cylindrical distribution of electrons within the Alfvén wing. Alternatively, we assumed the electron density to be constant along horizontal tubes parallel to the Juno-Earth line to get an average density along the portion of the line-of-sight traversing the Alfvén wing. Using these approaches led to electron densities up to 17,000-30,000 cm^-3 .

How to cite: Caruso, A., Buccino, D., Coffin, D., Gomez Casajus, L., Parisi, M., Zannoni, M., Gramigna, E., Withers, P., Tortora, P., Park, R. S., Steffes, P., and Bolton, S.: Io's Alfvén Wing Electron Density Measured by Juno Radio Occultations, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-726, https://doi.org/10.5194/epsc2024-726, 2024.

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NASA's Juno mission has been studying Jupiter since 2016 from a polar, highly elliptical orbit. While not its primary goal, Juno has captured images and spectra of Jupiter's Galilean moons from advantageous positions using onboard cameras: JIRAM (Jovian InfraRed Auroral Mapper - infrared), JunoCam (visible), and SRU (Stellar Reference Unit - visible). Specifically, JIRAM is an instrument that combines a dual-band imager and spectrometer. Its imager has a single detector capable of capturing 2D images through two different filters: L band (3.3 to 3.6 µm) and M band (4.5 to 5 µm). The angular resolution of its pixels (0.01°) is sufficient for moon imaging, though the spatial resolution varies based on the spacecraft's distance from the moons. Initially around 100 km/pixel, it has improved to about 500 m/pixel during the closest approaches of Juno to Io. This study focuses on analyzing JIRAM's high-resolution images to understand the location, shape, and some thermal characteristics of volcanic thermal sources on the moons. Recent findings from data collected by NASA's Juno mission unveil shared thermal attributes among approximately 50 paterae on Io, Jupiter's moon. These features exhibit conspicuous "thermal rings," indicative of elevated temperatures, encircling their central floors. Prominent examples, including Loki, Surt, Fuchi, Amaterasu, Mulungu, Chors, and Dazhbog Patera, alongside numerous others, display such consistent surface temperature pattern. Analysis of this novel Juno/JIRAM dataset suggests that the presence of hot rings surrounding paterae is a prevalent occurrence, likely signaling the presence of active lava lakes. Notably, most scrutinized paterae lack recent lava flows on their flanks, implying that during the observation period, the lava lake levels remained below the rim. These findings offer valuable insights into the dynamic activity of paterae, suggesting potential mechanisms such as central magma upwelling or cyclical vertical movements akin to a piston. The intense tidal forces experienced by Io may contribute to these phenomena.The distribution of these lava lakes across the moons is investigated, anc comparisons with visible light images are also made. Notably, Loki Patera exhibits numerous islands in the same positions as seen in previous visible light images from Voyager, suggesting a consistent lava level. 

Figure 1: Loki Patera as seen from Voyager (left, in the visible) and from JIRAM (right, in the infrared)

Figure 2: Pfu 1063 as seen by JIRAM

Acknowledgments

This work is supported by the Agenzia Spaziale Italiana (ASI). JIRAM is funded by the ASI–INAF Addendum n. 2016-23-H.3-2023 to grant 2016-23-H.0. Part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.

How to cite: Mura, A., Tosi, F., Lopes, R., Zambon, F., Sordini, R., Bolton, S., Mouginis-Mark, P., Rathbun, J., Becker, H., Hansen-Koharchek, C., Adriani, A., Plainaki, C., Sindoni, G., Mirino, M., Nodjoumi, G., and Pettine, M.: Exploring the Distribution and Dynamics of Lava Lakes on Io: Insights from Juno Mission Data, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-528, https://doi.org/10.5194/epsc2024-528, 2024.

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During the Juno extended mission, the spacecraft passed Jupiter’s Galilean moons, Ganymede, and Europa, and then Io respectively.  The flyby of Ganymede was in June 2021, at a distance of ~1000 km, and in September 2022, the spacecraft flew by Europa at a distance of ~350 km.  Two flybys of Io at a distance of 1500 km occurred in December 2023 and February 2024. The close flybys were the first encounters with the moons in over two decades and provided the first opportunity to probe their subsurface at multiple microwave frequencies using Juno’s Microwave Radiometer (MWR).  The observations provided several swaths across the moons at six frequencies, ranging from 600 MHz to 22 GHz.

Early radar results of Jupiter’s icy moons dating back several decades identified the moons as extremely bright objects with significant radar scattering (Ostro et al., 1980).  Comparisons of the radar properties of Europa & Ganymede indicated important differences in the radar signatures from each other and our Moon (Ostro et al., 1992).  Possible explanations included modulations in porosity (Ostro and Shoemaker, 1990), random facets, larger than the observed wavelengths (Goldstein and Green, 1980), and the idea that the top meters of ice covering their surfaces may be crazed, fissured, and/or filled with jagged ice boulders (Goldstein and Green 1980).

The Juno MWR observations represent the first resolved interrogation of the moons Ganymede, Europa and Io’s subsurface structure.  For icy bodies such as Ganymede and Europa, the MWR observed brightness temperature, T_B,  is dependent on such ice shell parameters as ice purity, the thermal structure of the icy shell (providing a constraint on the global heat flux) as well as the distribution of internal microwave scattering, thus allowing MWR to provide integral constraints on these shell properties. The MWR observations of Ganymede showed T_B generally increases with depth, has a significant reflected synchrotron radiation component at the lowest MWR frequency, 600 MHz, and was well correlated with terrain type.  The T_B was generally anticorrelated with visible reflectivity (albedo).  hermal gradient from deepest channels constrains heat flux (and thickness of conductive ice shell).  Analysis of the MWR results at Ganymede provided a new constraint on Ganymede’s heat flux and shell thickness (conductive and total).  Using a thermal model based on modified Mixing Length Theory from Kamata et al. (2018) and a Radiative transfer model accounts for microwave radiation propagation through the ice shell including the effect of synchrotron and galactic reflected radiation the results suggest a heat flux of  mW/m² assuming pure ice.  The model suggests a thickness of conductive ice shell of   km

The surface of Jupiter’s moon Europa mapped by MWR covers a latitude range from ~20^oS to ~50^oN and a longitude range from 70^oW to 50^oE.  At these frequencies, the emission originates well beneath the nearly-transparent surface, probing from as deep as 28 km (at 0.6 GHz) and less than 20 m (at 22 GHz), depending on the purity of the ice.  At these frequencies, the emission originates well beneath the nearly-transparent surface, probing from as deep as 28 km (at 0.6 GHz) and less than 20 m (at 22 GHz), depending on the purity of the ice.  Microwave reflection plays an important role, and MWR data suggest the presence of small (radius a few cm) scatterers at depths of many meters.  Spatial variation is dominated by reflection, especially for the higher-frequency channels, and correlates with terrain type.  T_B is generally lower than the expected physical temperature of the ice, indicating strong microwave reflection of the cold sky. 

The slope of the spectra indicates successively more reflection with decreasing frequency, down to ~2.5 GHz.  T_B varies across Europa, much more than the expected variation in ice temperature, implying the amount of reflection must also vary.  The spectra from different locations are nearly parallel, suggesting all frequencies see a common set of reflectors.  No evidence of diurnal variation is observed in the MWR data, indicating even the highest frequency channel is probing beneath the diurnal layer.  Using a simple model, and minimal assumptions the MWR data suggest the presence of volume scattering small reflectors extending to ~1 km depth. 

At Io, the first fly-by observed Io’s north pole and the 2^nd pass mapped latitudes within +/- 45^o on the Jovian facing hemisphere. The broad frequency range of the MWR probes successively deeper into the Io sub-surface with the 0.6GHz channel probing the deepest.  The sub-surface temperature, dielectric and surface roughness properties are encoded in the spectra obtained by the MWR. Here we report on the first spatially resolved observations of Io at frequencies below 22 GHz.  We find the brightness temperatures decrease with increasing latitude and are coldest at the north pole, consistent with prior infrared observations of the surface skin temperature. We observe a strong spectral gradient in the lowest frequency channels (increasing with depth) reflecting the sub-surface temperature profile from which we can infer endogenic heat flow. A large specular component of the surface microwave reflection, constrains the surface roughness. MWR provides first maps of sub-surface thermal profile and constraints on surface material properties.  Prior infrared thermal measurements only sense very top surface (skin layer).  Results indicate a surface that is very close to specular (in microwave) – meaning the surface is relatively flat (on ~meter scales) as viewed by MWR (100 km spatial scale).  The surface dielectric constant is close to 3, suggesting a relatively low density surface layer. Preliminary analysis suggests evidence that that MWR may be able to constrain the sub-surface thermal gradient (internal heat from Io).

These unprecedented measurements of Io, Europa and Ganymede will allow comparative studies of their surfaces and subsurface structures. The Juno MWR measurements complement previous ground-based radar and microwave radiometry observations, which provided early characterization of these surfaces.  A comparison of the microwave spectra for all three satellites will be presented, as well as a detailed analysis and interpretation of the Ganymede MWR data that provide new constraints on ice subsurface properties. 

How to cite: Bolton, S., Zhang, Z., Brown, S., Levin, S., Ermakov, A., Akiba, R., Lunine, J., Feng, J., Hand, K., Keane, J., Misra, S., Hartogh, P., Stevenson, D., Siegler, M., and Bonnefoy, L.: Juno Microwave Radiometer Observations into the Subsurface of the Ice Shells of Io, Europa and Ganymede, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-291, https://doi.org/10.5194/epsc2024-291, 2024.

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Io, the most volcanically active body of the Solar System, has been the target of numerous ground-based and remote sensing observations over the past decades, improving our knowledge about the satellite.

Recent studies, based on data acquired by the Jovian InfraRed Auroral Mapper (JIRAM) [1] on board the Juno mission, confirm the presence of hundreds of hot spots [2,3,4]. New observations of Io obtained by JIRAM from Juno perijove 41 up to 53 provided very good spatial coverage of the northern hemisphere and a partial coverage of the southern hemisphere with a spatial resolution ranging between 27 and 9 km/pixel (Fig. 1). Furthermore, the very last observations reaching a spatial resolution of a few km/pixel, revealed unseen details of about ninety paretae, confirming the presence of several lava lakes [5] and allowing for a detailed study of their morphology [6]. 

In this work, we consider the JIRAM M-filter images centered at 4.8 µm, to integrate and improve the results obtained by [3]. We selected images from orbits 41-53, characterized by an unprecedented spatial resolution and negligible radiance saturation of the detector. For each orbit, we identify the hot spots giving priority to images with higher spatial resolution in case of data redundancy, to monitor the overall total spectral radiance distribution across the satellite and the temporal variability of each hot spot, if covered by multiple Juno orbits [7]. Thanks to these new dataset, we are able to better identify hot spots unresolved in [3], and locate new small and faint hot spots. Moreover, the good high spatial resolution coverage of the northern hemisphere (Fig. 2) allows to distinctly discern hot spots in this region, as well as in the rest of the satellite. JIRAM data represent a unique chance to study Io’s surface. In the next future, the spatial coverage will be increased by JIRAM observations following orbits 53, including also the southern polar region. This will be fundamental for a comprehensive understanding of this intriguing satellite. 

Acknowledgments

This work is supported by the Agenzia Spaziale Italiana (ASI). JIRAM is funded by the ASI–INAF Addendum n. 2016-23-H.3-2023 to grant 2016-23-H.0. Part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.

References

[1] Adriani, A., et al. (2017). JIRAM, the Jovian infrared auroral mapper. SSR, 213(1–4), 393– 446. [2] Mura, A., et al. (2020). Infrared observations of Io from Juno. Icarus 341, 113607. [3] Zambon, F., et al. (2023). Io Hot Spot Distribution Detected by Juno/JIRAM. GRL, 50, e2022GL100597. [4] Davies, A. et al. (2024). Io's polar volcanic thermal emission indicative of magma ocean and shallow tidal heating models. Nat. Ast., Vol. 8, p. 94-100. [5] Mura A. et al. (2024). Hot rings on Io observed by Juno/JIRAM. Nature Communications Earth & Environment, in press. [6] Mirino, M. et al. (2024). Morphological characterization of Io’s Paterae  and their geological context. EPSC. [7] Mura, A. et al. (2024). The temporal variability of Io's hotspots. Frontiers in Astronomy and Space Sciences, in press.

Figure 1: Io global radiance map from Juno PJ51.

Figure 2: Io northern polar region radiance map from PJ51 at 9 km/pixel (JIRAM image JM0510_2023-05-16T03-13-11).

How to cite: Zambon, F., Mura, A., Lopes-Gautier, R. M., Tosi, F., Rathbun, J., Pettine, M., Mirino, M., Nodjoumi, G., Castagnoli, C., Cicchetti, A., Moirano, A., Noschese, R., Sordini, R., Plainaki, C., Sindoni, G., Hansen-Koharcheck, C., Becker, H., and Bolton, S.: Io JIRAM observations from Juno orbits 41-53, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-502, https://doi.org/10.5194/epsc2024-502, 2024.

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Introduction: Jupiter’s moon Io is the most volcanically active body in our Solar System [e.g., 1]. Its surface is enriched of volcanism products such as widespread lava flows and pyroclastic deposits which suggest the presence of both effusive and explosive eruptions [1]. Among the candidate volcanic explosive centers are irregular and complex craters with scalloped edges, steep walls, and flat floors called paterae [2]. By their morphology, paterae have been interpreted as candidate caldera created by the collapse of magmatic chambers [2]. This interpretation is supported by their irregular arcuate shape and their association with mountains or plateaus which suggest tectonic influences [e.g., 2]. However, the debate of their formation and their geological nature is still active and under study, since data resolution from the image mosaic obtained from past NASA Galileo and Voyager missions is not always high enough to allow a deeper morpho-geological analysis of all the paterae identified on the surface [e.g., Fig. 1d].

     In recent years, remote sensing instruments onboard the NASA Juno mission [3] collected Io data at increasingly higher spatial resolution [e.g., 4]. The resolution attained in three orbits in 2023 (49, 51, 53) has allowed to observe both the morphology and the reflectance proprieties of Io’s paterae with unprecedented detail (Fig. 1). Paterae’s morphological characteristics have been observed and revealed by extracting information from a larger dataset including: (i) The Global image mosaic obtained from Galileo-Voyager [5], (ii) the Global Digital Terrain Model [6], (iii) the global USGS Io’s geological map [1], (iv) Juno/JunoCam  [7], and (v) Juno/JIRAM [8]. The morphological analysis has been performed considering the planimetric view (walls and floors) and the transversal cross section. We have added the features which are often associated with paterae (such as lateral flows) and the geological units which are related with each studied patera. Then, we have used the images of paterae as observed by JunoCam to interpret the flux variability and distribution on the surface of the studied features to support geological interpretation for the paterae morphological aspect, evolution, and activity. The ESRI ArcGIS software has been used for this study. Here, we report the results of a morphological breakdown of Io’s paterae performed at different levels, by using the visible images from the global mosaic and the latest images from JunoCam, coupled with infrared data collected by JIRAM. Then, we present statistics and the global distribution of the various patera types based on the different levels of the classification framework (example in Fig.2).

Figure 1: Examples of different morphological characteristics of paterae on Io’s surface as seen from visible images (global Galileo/Vikings mosaic) and JUNO-JIRAM processed images. Example of all paterae classified as active by using  JIRAM radiance data and as a- Rounded, b- Irregular, c- Elongated and d-N/A in visible images.  

Figure 2: Example of a global view of Io’s surface presenting a preliminary global survey performed by using only information from the Global image mosaic. Paterae extracted from the JUNO orbits 41-49 have been classified as rounded (green dots), irregular (red dots), elongated (yellow dots), and not available (N/A) when the resolution was not enough to get the information (blue dots).  White dots indicate the position of the other paterae mapped on the surface of the moon from the other orbits.

Acknowledgments: This work is supported by the Agenzia Spaziale Italiana (ASI). JIRAM is funded by the ASI–INAF Addendum n. 2016-23-H.3-2023 to grant 2016-23-H.0. Part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.

References: [1] Williams et al., (2011), Geological Survey Scientific Investigations Map 3168, https://pubs.usgs.gov/sim/3168/. [2] Radebaugh et al., (2001), Journal of Geophysical research,  https://doi.org/10.1029/2000JE001406. [3] Bolt et al., (2017), Space Science Review, https://doi.org/10.1007/s11214-017-0429-6. [4] Mura et al., (2020), Icarus, https://doi.org/10.1016/j.icarus.2019.113607.  [5] Becker & Geisslet, (2005), Lunar and Planetary Institute Science Conference Abstracts 36. URL: http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1862.pdf  [6] Kersten et al., (2021), Planetary and Space Science, https://doi.org/10.1016/j.pss.2021.105310. [7] Orton et al., (2017), Geophysical Research Letter,  https://doi.org/10.1002/2016GL072443. [8] Noschese et al., (2020), Advance in Space Research, https://doi.org/10.1016/j.asr.2019.09.052

How to cite: Mirino, M., Mura, A., Zambon, F., Tosi, F., Nodjoumi, G., Bolton, S., Ravine, M., Hansen-Koharcheck, C., Bagenal, F., Lopes, R., Sindoni, G., and Plainaki, C.: Morphological characterization of Io’s paterae and their geological context., Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-547, https://doi.org/10.5194/epsc2024-547, 2024.

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Introduction

NASA’s Juno spacecraft, orbiting Jupiter, had three close encounters with Io in 2023 and 2024, during which JunoCam acquired ~20 visible color images at 1 to 12 km/pixel.  The area covered by these images included high latitudes not well imaged on previous missions.  These images show significant changes from previous imaging.  JunoCam also observed a total of nine plumes associated with volcanic features. 

JunoCam instrument

JunoCam has a CCD detector with a strip filter array enabling imaging in three color bands—blue, green and red  (Hansen et al. [1]).  The JunoCam lens maps 58° across the 1600 pixel detector width, which is scanned by spacecraft rotation. Repeated readout of the of the CCD provides overlapping coverage in each band.  A color image is generated by reprojecting each “framelet” so that each color can be mosaicked and the three colors can be composited. 

Io Encounters

During the Juno extended mission (2021-present), Juno had multiple flybys of Io, the best of which occurred associated with  perijove passes PJ57, PJ58 and PJ60.  On PJ57 (30 December 2023), JunoCam imaged Io’s high northern latitudes from as close as 2,800 km, with a scale as small as 1.9 km/pixel (Figure 1).  The dayside JunoCam images from the PJ58 Io encounter (3 February 2024) covered the mid-latitudes from as close as 3,800 km and a scale of 2.6 km/pixel (Figure 2).  JunoCam also captured nightside images, illuminated by Jupiter.  While the signal levels were lower in these images, the scale was as small as 1.0 km/pixel.  Most recently, the PJ60 Io encounter (9 April 2024) images were from a greater distance (17,300 km) and with a larger scale (11.7 km/pixel), but they did provide coverage of the high southern latitudes. 

Results

Figure 3 shows a map of Io, assembled from JunoCam coverage from PJ55, 57, 58 and 60.  The map indicates the locations of surface changes either from lava flows or volatiles deposits from the JunoCam images.

Changes

Some instances of changes observed by JunoCam are as follows:

• Kanehekili Fluctus (17.2° S, 33.4° W):  Kanehekili was imaged by Jupiter-shine on PJ58 at 1.8 km/pixel.  It appears as an integrated, single flow field, 210 kilometers north-south and 120 kilometers east-west, similar to its appearance in the Voyager imaging, but different from the two distinct flow fields in the Galileo coverage. JunoCam also shows a large, diffuse red deposit fanning out from the western side. 
• East of Kanehekili (17.7° S, 23.2° W):  about 300 km east of Kanehekili, is a feature that was not seen previously, with two long, thin sets of flows, running roughly to the west and southwest from the active volcanic region at 17.2° S, 21.9° W.  A diffuse red deposit, 60 by 90 km, is just to the east of this source.  The terminal ends of the flows are surrounded by dark gray diffuse deposits, ~100 km across. 
• Masubi Fluctus (43° S, 52.5° W):  JunoCam imaged Masubi  by Jupiter-shine on PJ58 and PJ60.  Two new flows formed at Masubi since the New Horizons observations of 2007, running south and east from common source. The eastern flow is 120 kilometers long, while the southern flow is 170 kilometer long. The eastern flow has two distal flow lobes, each with associated dark and bright diffuse deposits.
• Nusku Patera (65° S, 3.6° W):  in the sixty-six days between Juno’s PJ58 and PJ60 encounters of Io, a circular red ring, 1100 km in diameter, formed around Nusku Patera, likely from a large, Pele-type plume rich in S₂.

High phase albedo reversal

The PJ58 encounter acquired images with phase angles ranging from ~130° for the first to ~90° for the fourth.   This sequence shows the floors of three paterae quite bright at high phase.  The floor of Loki (Figure 4), progresses from whiteish gray at high phase to darker gray at lower phase (though still brighter than the near-black seen low phase).  This phase dependence would be expected from a surface with significant areal fraction of glassy component at the sub-pixel scale, like fresh lava flows. 

Plumes

Nine volcanic plumes were identified in JunoCam images (Figure 5).  Four came from active volcanic regions without previous plume detections (Seth, Mixcoatl, Tonatiuh, and Culann).  Estimated heights of these plumes ranged from 50 to 100 km.  These heights and brightness in the red-filter framelets suggest they are SO₂ and dust-rich “Prometheus” type plumes.  The plumes at Kanehekili, Masubi, Tonatiuh, Volund, and Xihe are associated with regions of flow-like surface changes, consistent with them being caused by mobilization of surface volatiles. Multiple plume columns were observed at Xihe and Kanehekili during the PJ58 encounter, suggesting multiple active flow lobes at these locations.

Acknowledgements

This work was funded by the National Aeronautics and Space Administration through the Juno Project. Junocam images are available at https://www.missionjuno.swri.edu and are archived with NASA’s Planetary Data System (PDS).  

References

[1] Hansen, C. J., et al. Junocam: Juno’s outreach camera. Space Sci. Rev. 2014. doi10.007/s/11214-014-0079-x

Figures

Figure 1. JunoCam PJ57 Io encounter image sequence (the first image shows Io illuminated by Jupiter-shine).

Figure 2. JunoCam PJ58 Io encounter image sequence (the first two images show Io illuminated by Jupiter-shine).

Figure 3. Io mapped with JunoCam (PJ55, 57, 58 and 60), indicating changes or activity.  Cyan ovals denote areas of new, faded, or shifted plume and/or volatile deposits. Yellow ovals denote areas of probable new lava flows.

Figure 4. Four views of Loki Patera from PJ58, time progressing left to right.  Because of encounter trajectory, the phase angle progresses from ~130° in the leftmost image to ~90° in the rightmost image.  Note the darkening of the floor of Loki as the phase angle decreases, while the rest of the region shown appears the same.

Figure 5. Plumes observed by JunoCam: a) Xihe double plume observed during orbit 58 (02/2024); b) Prometheus plume observed during orbit 55 (10/2023); c) Prometheus (left) and Seth (right) plumes observed during orbit 60 (04/2024); d) Volund plume observed during orbit 55; e) Mixcoatl plume observed during orbit 60; f) Kanehekili double plume observed during orbit 58; g) Tonatiuh plume observed at the terminator during orbit 17 (12/2018).

How to cite: Ravine, M., Hansen, C., Caplinger, M., Schenk, P., Lipkaman Vittling, L., Krysak, D., Perry, J., Williams, D., Radebaugh, J., Pettine, M., Keane, J., Hayes, A., Rathbun, J., and Bolton, S.: Results from recent close-up imaging of Io by JunoCam (perijoves 57, 58 and 60), Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-731, https://doi.org/10.5194/epsc2024-731, 2024.

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