Ganymede MHD Model: Magnetospheric Context for Juno's PJ34 Flyby

On June 7th, 2021 the Juno spacecraft visited Ganymede and provided the first in situ observations since Galileo's last flyby in 2000. The measurements obtained along a one-dimensional trajectory can be brought into global context with the help of three-dimensional magnetospheric models. Here we apply the magnetohydrodynamic model of Duling et al. (2014) to conditions during the Juno flyby. In addition to the global distribution of plasma variables we provide mapping of Juno's position along magnetic field lines, Juno's distance from closed field lines and detailed information about the magnetic field's topology. We find that Juno did not enter the closed field line region and that the boundary between open and closed field lines on the surface matches the poleward edges of the observed auroral ovals. To estimate the sensitivity of the model results, we carry out a parameter study with different upstream plasma conditions and other model parameters

The Jovian ionospheric conductivity derived from a broadband precipitated electron distribution

The Pedersen ionospheric conductivity and conductance at Jupiter are computed assuming a broadband precipitating-electron flux and compared to values obtained when assuming a mono-energetic precipitating-electron flux. Among other results, it is found that the ratio between the broadband and the mono-energetic conductances depends on the electron mean energy of the precipitating-electron population. For a mono-energetic distribution, an optimal energy exists, around 30-40 keV, for which the conductance arising from the precipitation is maximal. If the mean electron energy is well below this optimal energy, the conductance calculated for a broadband distribution is enhanced compared to the mono-energetic case because part of the electron energy distribution reaches this optimal level. The conductance is also underestimated for a mono-energetic electron precipitation well above the optimal value. The opposite trend is observed around the optimal energy as most of the electrons of the broadband distribution have either lower or higher energies, while all electrons of the mono-energetic distribution have an energy close to the optimum

The complex behavior of the satellite footprints at Jupiter: the result of universal processes?

At Jupiter, some auroral emissions are directly related to the electromagnetic interaction between the moons Io, Europa and Ganymede on one hand and the rapidly rotating magnetospheric plasma on the other hand. Out of the three, the Io footprint is the brightest and the most studied. Present in each hemisphere, it is made of at least three different spots and an extended trailing tail. The variability of the brightness of the spots as well as their relative location has been tentatively explained with a combination of Alfvén waves’ partial reflections on density gradients and bi-directional electron acceleration at high latitude. Should this scenario be correct, then the other footprints should also show the same behavior. Here we show that all footprints are, at least occasionally, made of several spots and they all display a tail. We also show that these spots share many characteristics with those of the Io footprint (i.e. some significant variability on timescales of 2-3 minutes). Additionally, we present some Monte-Carlo simulations indicating that the tails are also due to Alfvén waves electron acceleration rather than quasi-static electron acceleration. Even if some details still need clarification, these observations strengthen the scenario proposed for the Io footprint and thus indicate that these processes are universal. In addition, we will present some early results from Juno-UVS concerning the location and morphology of the footprints during the first low-altitude observations of the polar aurorae. These observations, carried out in previously unexplored longitude ranges, should either confirm or contradict our understanding of the footprints

Juno-UVS Observations of Io during the PJ58 Flyby

peer reviewedCurrently in its first extended mission, NASA’s Juno spacecraft has made several close approaches to Jupiter’s Galilean satellites.  The final of these very close flybys will be of Io during the perijove (PJ) 58 orbit, scheduled to occur at 17:48:35 UTC on 3 Feb. 2024, about 3h59m prior to PJ58. Juno’s Ultraviolet Spectrograph (UVS) is a photon-counting far-ultraviolet (FUV) imaging spectrograph with a bandpass of 68-210 nm, which will be used to observe Io’s numerous FUV emissions during the flyby. The circumstances of the flyby are similar to that for Ganymede during PJ34 at 16:56 UTC on 7 June 2021, with the satellite only observable for a few minutes on either side of Juno’s closest approach. We plan to record data +/-5 min (at best 20 swaths of data) about the closest approach time hoping for a significant decrease in the high radiation background due to shielding provided by Io itself.  Our observations will range from an altitude of 1500 km (closest approach) to 7820 km, giving the UVS data an expected spatial resolution of 6 to 28 km at the sub-spacecraft point.  As with the similar close flyby of Ganymede (Greathouse et al. 2022; Molyneux et al. 2022), UVS will attempt to measure reflected FUV sunlight from the surface of Io and airglow emissions from oxygen and in this case sulfur atoms. These observations will be more challenging than at Ganymede, however, since the background due to penetrating (>10 MeV) electrons at Io is expected to be a factor of 10 or more larger than at Ganymede. In this talk we will present results from the initial reduction and analysis of the UVS data obtained during the flyby of Io

The Io, Europa and Ganymede auroral footprints at Jupiter in the ultraviolet: positions and equatorial lead angles

Jupiter's satellite auroral footprints are a consequence of the interaction between the Jovian magnetic field with co-rotating iogenic plasma and the Galilean moons. The disturbances created near the moons propagate as Alfv\'en waves along the magnetic field lines. The position of the moons is therefore "Alfv\'enically" connected to their respective auroral footprint. The angular separation from the instantaneous magnetic footprint can be estimated by the so-called lead angle. That lead angle varies periodically as a function of orbital longitude, since the time for the Alfv\'en waves to reach the Jovian ionosphere varies accordingly. Using spectral images of the Main Alfv\'en Wing auroral spots collected by Juno-UVS during the first forty-three orbits, this work provides the first empirical model of the Io, Europa and Ganymede equatorial lead angles for the northern and southern hemispheres. Alfv\'en travel times between the three innermost Galilean moons to Jupiter's northern and southern hemispheres are estimated from the lead angle measurements. We also demonstrate the accuracy of the mapping from the Juno magnetic field reference model (JRM33) at the completion of the prime mission for M-shells extending to at least 15RJ . Finally, we shows how the added knowledge of the lead angle can improve the interpretation of the moon-induced decametric emissions.Comment: 20 pages, 8 figures, Accepted for publication in Journal of Geophysical Research: Space Physics on 20 April 202

Jupiter’s auroras during the Juno approach phase as observed by the Hubble Space Telescope

We present movies of the Hubble Space Telescope (HST) observations of Jupiter’s FUV auroras observed during the Juno approach phase and first capture orbit, and compare with Juno observations of the interplanetary medium near Jupiter and inside the magnetosphere. Jupiter’s FUV auroras indicate the nature of the dynamic processes occurring in Jupiter’s magnetosphere, and the approach phase provided a unique opportunity to obtain a full set of interplanetary data near to Jupiter at the time of a program of HST observations, along with the first simultaneous with Juno observations inside the magnetosphere. The overall goal was to determine the nature of the solar wind effect on Jupiter’s magnetosphere. HST observations were obtained with typically 1 orbit per day over three intervals: 16 May – 7 June, 22-30 June and 11-18 July, i.e. while Juno was in the solar wind, around the bow shock and magnetosphere crossings, and in the mid-latitude middle-outer magnetospheres. We show that these intervals are characterised by particularly dynamic polar auroras, and significant variations in the auroral power output caused by e.g. dawn storms, intense main emission and poleward forms. We compare the variation of these features with Juno observations of interplanetary compression regions and the magnetospheric environment during the intervals of these observations

The two faces of the Jovian UV aurorae

Being mostly connected via closed magnetic field lines, the aurorae at the two poles display two broadly similar signatures of the same magnetospheric processes. However, differences are sometimes observed, indicative of asymmetries either in the polar regions (e.g. different solar illumination, magnetic anomalies, etc.) or in the magnetosphere (e.g. twisting of the magnetotail), thus showing two complementary sides of the magnetosphere-ionosphere coupling.</p><p>Whatever the planet, seeing the aurorae on both poles at the same time is challenging. Either both polar regions can be seen at once, but then only from the side, with poor spatial coverage (especially close and beyond the limb), or we need (at least) two observatories. Here we use the latter option to observe the two faces of the UV aurorae on Jupiter. In the last years, several Hubble Space Telescope observations with the Space Telescope Imaging Spectrograph (STIS) have been planned during close-up perijove observations of the poles with the UV spectrograph (UVS) on board the Juno spacecraft. The aurorae at Jupiter can be divided into three main components, with the Main Emissions, a quasi-continuous, but sometimes irregular, ribbon of auroral emissions, delimitating the outer emissions outside of it and the polar emissions inside of it. We compare the global morphology and the relative power emitted by the different auroral features in these three regions. Former studies also indicated that synchronized quasi-periodic flares could be observed in both hemispheres and we will look after similar events in this new dataset. Finally, even if the observations are delayed by approximately one hour, we can still compare the mean emitted power before (north) and after (south) each Juno perijove to look for a global trend.</p&gt

Preliminary Results from a Coordinated Hisaki/Chandra/XMM-Newton Study of the Jovian Aurora and Io Plasma Torus

We present preliminary results from a coordinated Hisaki/Chandra/XMM-Newton observational campaign of the Jovian aurora and Io plasma torus. The data were taken over a three week period in April, 2014. Jupiter was observed continuously with Hisaki, six times with the Chandra/HRC instrument for roughly 12 hours per observation, and twice by XMM-Newton. The goal of this observational campaign was to understand how energy and matter are exchanged between the Jovian aurora, the IPT, and the Solar wind. X-ray observations provide key diagnostics on highly stripped ions and keV electrons in the Jovian magnetosphere. We use the temporal, spatial, and spectral capabilities of the three instruments to search for correlated variability between the Solar wind, the EUV-emitting plasma of the IPT and UV aurora, and the ions responsible for the X-ray aurora. Preliminary analysis suggests a strong 45 min periodicity in the EUV emission from the electron aurora. There is some evidence for complex variability of the X-ray auroras on scales of tens of minutes. There is also clear morphological changes in the X-ray aurora that do not appear to be correlated with either variations in the IPT or Solar wind

Jupiter observations at infrared wavelengths by Juno

The Jovian InfraRed Auroral Mapper (JIRAM) [1] on board the Juno [2,3] spacecraft, is equipped with an infrared camera and a spectrometer working in the spectral range 2-5 _m. JIRAM was built to study the infrared aurora of Jupiter and to map the planet's atmosphere in the 5 μm spectral region. Its spectroscopic observations in the 2-5 μm range can be used for studying atmospheric dynamics, clouds and measuring the abundance of certain trace species that are important to atmospheric chemistry, microphysics and dynamics such as water, ammonia and phosphine and for the formation of the infrared aurora like the ion H3+.The instrument has operated during most of the Jupiter flybys since science mission started in August 2016 performing several observations of the of the planet from the equator to poles. Unprecedented views of the polar atmospheric structures and auroras have been observed for the first time thanks special nature of Juno's orbit. We present an overview of the most significant observations done by the instrument since the start of the mission.[1] Adriani A. et al., JIRAM, the Jovian Infrared Auroral Mapper. Space Sci. Rew., DOI 10.1007/s11214-014-0094-y, 2014.[2] Bolton S.J. et al., Jupiter's interior and deep atmosphere: The initial pole-to-pole passes with the Juno spacecraft. Science DOI: 10.1126/science.aal2108, 2017.[3] Connerney J. E.P. et al., Jupiter's magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits. Science, DOI: 10.1126/science.aam5928, 2017

A Preliminary Study of Magnetosphere-Ionosphere-Thermosphere Coupling at Jupiter: Juno Multi-Instrument Measurements and Modeling Tools

The dynamics of the Jovian magnetosphere are controlled by the interplay of the planet's fast rotation, its main iogenic plasma source and its interaction with the solar wind. Magnetosphere-Ionosphere-Thermosphere (MIT) coupling processes controlling this interplay are significantly different from their Earth and Saturn counterparts. At the ionospheric level, they can be characterized by a set of key parameters: ionospheric conductances, electric currents and fields, exchanges of particles along field lines, Joule heating and particle energy deposition. From these parameters, one can determine (a) how magnetospheric currents close into the ionosphere, and (b) the net deposition/extraction of energy into/out of the upper atmosphere associated to MIT coupling. We present a new method combining Juno multi-instrument data (MAG, JADE, JEDI, UVS, JIRAM and Waves) and modeling tools to estimate these key parameters along Juno's trajectories. We first apply this method to two southern hemisphere main auroral oval crossings to illustrate how the coupling parameters are derived. We then present a preliminary statistical analysis of the morphology and amplitudes of these key parameters for eight among the first nine southern perijoves. We aim to extend our method to more Juno orbits to progressively build a comprehensive view of Jovian MIT coupling at the level of the main auroral oval