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Juno’s highly elliptical polar orbit offers unique in-situ measurements of the electrodynamic interaction between Jupiter and its moon Io. These occur both near Io and near the surface of Jupiter and at distances between. Magnetic field data obtained during multiple traversals of magnetic field lines connected to the orbit of Io reveal remarkably rich and complex current densities along flux tubes connected to Io’s position along its orbit. Using Juno’s many traversals of Io's flux tube (IFT), we derive a model of the strength of the interaction with regards to distance along Io’s extended tail and Io’s position in the plasma torus, illuminating the interaction of Jovian magnetospheric plasma with Io and setting important constraints in the Io-Jupiter interaction.The model is based on an inverse methodology to distribute currents along the IFT in such a way as to match the magnetic field signature observed during Juno’s traversals of the IFT as well as passages near the IFT. We derive, by means of non-linear optimization, the distribution of current within the IFT (during traversals) as well as the size and morphology of the IFT that best fits the magnetic field observations. We compare our results with observations of the IFT obtained near Io as Voyager 1 passed nearby.

Since Juno’s orbit insertion, the attitude reference for the MAG investigation onboard Juno, the micro Advanced Stellar Compass (µASC), and as a part of its additional functionality, continuously measures high energy electron fluxes in Jupiter’s magnetosphere. The µASC camera head unit (CHU) sensitivity to electrons with kinetic energy greater than 15 MeV and protons with energies >80MeV, provides a means of in-situ mapping of electron fluxes sampled during 47 Juno orbits.The focus of this study are events observed when Juno is traversing M-shell of the Galilean moon, Europa, which shows distinctly different signature from that the other moons.We present µASC observations of energetic electrons interaction with Europa moon. Europa generates a wake, that affect the high energy electron driftshell, by scattering electrons into the loss-cone. The wake is then dissolved and these interactions are observed around 20° down tail. On the upstream side, the energetic drift shell is free from hard radiation as Europa acts as an obstacle for the energetic electrons. This assymetry result in a lower electon density on the upstream side resulting in an E-field filling in the e- population from surrounding driftshells in less than 10°.

Galactic cosmic rays (GCRs), primarily consisting of protons, are ubiquitous throughout the solar system. The greatest source is supernova activity and the flux in the solar system is modulated by the solar wind. Planets can be shielded if they possess a magnetic field. Jupiter’s magnetic field is the strongest in the solar system and has several interesting features such as the Great Blue Spot near the Equator. The JUNO satellite has mapped the magnetic field of Jupiter in great detail (Connerney et al, JGR Planets 127(2), 2022) resulting in the JRM33 model, composed of data from 32 polar orbits of JUNO around Jupiter.We have calculated a cosmic ray cutoff rigidity map for Jupiter. This was done using a modified version of a particle trajectory program (the Geomagnetic Cutoff Rigidity Computer Program by Smart and Shea (2001, Tech. Rep. No. 20010071975)) with the first 12 degrees and orders of the spherical harmonic expansion from the JRM33 model as input. This is done for vertical GCR entry into Jupiter’s atmosphere at a height of 67.5 km above the 1 bar level and for distances further out where high energy particles have been detected by JUNO. The energies required to enter into Jupiter’s atmosphere varies by several orders of magnitude from above 2500 GeV at locations around the Great Blue Spot and going downwards towards the poles.The modulation of the GCR proton flux into Jupiter’s atmosphere was then calculated. For the incoming GCR spectrum we used data from the BESS-POLAR II Antarctic mission (Abe et al, ApJ 822(2), 2016), collected at solar minimum where the modulation by the solar wind is at its lowest. By fitting the measured spectrum and using the calculated cutoff rigidities we have made a map of the proton flux into Jupiter’s atmosphere.Finally, we have investigated several incidents of high energy heavy ion detections by JUNO (Becker et al, JGR Planets 126, 2021) by calculating the cutoff rigidities from several incoming angles at the locations where JUNO made the detections and along the corresponding M-shells.

During transit from Earth to Jupiter, NASAs Juno spacecraft carried out scientific measurements along its trajectory, using a subset of its instrument suite. One of the instruments turned on during the journey was the micro Advanced Stellar Compass, part of the MAG investigation. The fully autonomous microASC uses a camera to image the sky for attitude determination, its primary function, but it also logs objects appearing multiple times in the camera FOV that are not found in the instrument’s star catalog. In doing so, it routinely logged the motion of illuminated spallation products evolving from the impacts of interplanetary dust particles (IDPs) on the spacecraft. The system is capable of detection of IDPs with a diameter larger than ~5µm, i.e. particles in the size range responsible for the Zodiacal light. The detection mode was activated just after Juno performed a deep space manoeuver at 2.2AU setting the spacecraft up for a gravity assist from a close Earth flyby, sending Juno on a trajectory to rendezvous with Jupiter. The first leg of the journey, from 2.2AU to 0.8AU and to the Earth flyby, was in the ecliptic plane, whereas the trajectory from Earth to Jupiter rose well above the ecliptic plane. This resulted in measured IDP density profiles both in and above the ecliptic plane. In December 2015, half a year before Jupiter orbit insertion, a conspicuously high rate of dust impacts was detected for a fortnight. A closer analysis showed that Juno happened to pass through the tail of a Jupiter family comet.We here present the observations of the particle population during the December 2015 event, discuss the dust tail evolution and morphology, and present the implications for the comet’s size and volatility.

The electromagnetic coupling between the Galilean satellites at Jupiter and the planetary ionosphere generates an auroral footprint, whose ultimate source is the relative velocity between the moons and the corotating magnetospheric plasma. The footprint can be detected in the infrared L band (3.3-3.6 microns) by the Jovian InfraRed Auroral Mapper (JIRAM) onboard the Juno spacecraft, which can observe the footprint position with high precision. Here, we report the JIRAM data acquired since August 27th 2016 until May 23rd 2022, corresponding to the first 42 orbits of Juno. The dataset is used to compute the average position of the footprint tracks of Io, Europa and Ganymede. The result of the present analysis can help to test the reliability of magnetic field models, to calibrate ground-based observations and to highlight episodes of variability in the footprint positions, which in turn can point out specific conditions of the Jovian magnetospheric environment.

We define the spatial clustering of X-rays within Jupiter’s northern auroral regions by classifying their distributions into ‘X-ray auroral structures’. Using data from Chandra during Juno’s main mission observations (24 May 2016 – 8 September 2019), we define five X-ray structures based on their ionospheric location and calculate the distribution of auroral photons. The morphology and ionospheric location of these structures allow us to explore the possibility of numerous X-ray auroral magnetospheric drivers. We compare these distributions to Hubble Space Telescope (HST)and Juno (Waves and MAG) data, and a 1D solar wind propagation model to infer the state of Jupiter’s magnetosphere. Our results suggest that the five sub-classes of ‘X-ray structures’ fall under two broad morphologies: fully polar and low latitude emissions. Visibility modelling of each structure suggests the non-uniformity of the photon distributions across the Chandra intervals are likely associated with the switching on/off of magnetospheric drivers as opposed to geometrical effects. The combination of ultraviolet (UV) and X-ray morphological structures is a powerful tool to elucidate the behaviour of both electrons and ions and their link to solar wind/magnetospheric conditions in the absence of an upstream solar monitor.

Jupiter’s upper atmosphere is considerably hotter than expected from the amount of sunlight that it receives1–3. Processes that couple the magnetosphere to the atmosphere give rise to intense auroral emissions and enormous deposition of energy in the magnetic polar regions, so it has been presumed that redistribution of this energy could heat the rest of the planet4–6. Instead, most thermospheric global circulation models demonstrate that auroral energy is trapped at high latitudes by the strong winds on this rapidly rotating planet3,5,7–10. Consequently, other possible heat sources have continued to be studied, such as heating by gravity waves and acoustic waves emanating from the lower atmosphere2,11–13. Each mechanism would imprint a unique signature on the global Jovian temperature gradients, thus revealing the dominant heat source, but a lack of planet-wide, high-resolution data has meant that these gradients have not been determined. Here we report infrared spectroscopy of Jupiter with a spatial resolution of 2 degrees in longitude and latitude, extending from pole to equator. We find that temperatures decrease steadily from the auroral polar regions to the equator. Furthermore, during a period of enhanced activity possibly driven by a solar wind compression, a high-temperature planetary-scale structure was observed that may be propagating from the aurora. These observations indicate that Jupiter’s upper atmosphere is predominantly heated by the redistribution of auroral energy., High-resolution observations confirm that Jupiter’s global upper atmosphere is heated by transport of energy from the polar aurora.

A key objective of the current Juno mission (Bolton et al., 2017, https://doi.org/10.1126/science.aal2108) is the direct determination of the secular variation (time dependency) of Jupiter's internal magnetic field in order to further understand the dynamics of Jupiter's interior. Here, we find that the residuals to a static, baseline model of the magnetic field are consistent with the effects of secular variation, specifically secular variation arising from zonal drift of the field. We present a technique for simultaneously inverting for the main magnetic field and secular variation due to zonal drift of the field. We explore the required drift systematically and argue that although the drift is dominated by a prograde super-rotation, corresponding to approximately 1 part in 106 relative to System IIIa (1965), there is also evidence for differential drift of the field. We compare the resultant secular variation with that determined by Moore et al. (2019, https://doi.org/10.1038/s41550-019-0772-5) and Connerney et al. (2022, https://doi.org/10.1029/2021je007055) and find good agreement. This suggests that the drift rate of Jupiter's magnetic field is steady over time periods of several decades, though short period secular variation (such as that resulting from torsional oscillations) superimposed on this steady secular variation is still possible.

The Juno Waves instrument measured plasma waves associated with Ganymede's magnetosphere during its flyby on 7 June, day 158, 2021. Three distinct regions were identified including a magnetotail/wake, and nightside and dayside regions in the main magnetosphere distinguished by their electron densities and associated variability. The main magnetosphere includes electron cyclotron harmonic emissions including a band at the upper hybrid frequency, as well as whistler-mode chorus and hiss. These waves likely interact with energetic electrons in Ganymede’s magnetosphere by pitch angle scattering and/or accelerating the electrons. The magnetotail/wake is accentuated by low-frequency turbulence and electrostatic solitary waves. Radio emissions observed before and after the flyby likely have their source in Ganymede’s magnetosphere.

The micro Advanced Stellar Compass (µASC), an attitude reference for the Juno Magnetic Field investigation, also continuously monitors high energy particle fluxes in Jupiter’s magnetosphere. ...

Jupiter’s aurora is complex and dynamic, with a large number of distinct auroral features and regions generated by multiple phenomena. Of these features, Io’s auroral signature is one of the most persistent and identifiable aurora, with a rich observational history spanning decades of remote observations. Since Juno arrived at Jupiter, providing in-situ transits through flux tubes directly connected to Io’s auroral emissions, its diverse set of instruments have revealed an even more complex and dynamic picture of Io’s auroral interaction. In this presentation, we report on Juno observations of precipitating electron fluxes connected to 18 crossings of Io’s footprint tail aurora, over altitudes of 0.15 to 1.1 Jovian radii (RJ). We will highlight how the strength of precipitating electron fluxes is dominantly organized by “Io-Alfvén tail distance”, the angle along Io’s orbit between Io and an Alfvén wave trajectory connected to the tail aurora. We will discuss how these fluxes were best fit with an exponential as a function of down-tail extent with an e-folding distance of 21˚, the acceleration region altitude likely increases down-tail, and most of the parallel electron acceleration sustaining the tail aurora occurs above 1 RJ in altitude. Finally, we will highlight how Juno has likely transited Io’s Main Alfvén Wing fluxtube, observing a characteristically distinct signature with precipitating electron fluxes ~600 mW/m2 and an acceleration region extending as low as 0.4 RJ in altitude.

International audience

NASA's Juno spacecraft has been orbiting Jupiter since August 2016, providing unprecedented insights into the giant planet's atmosphere. The Jupiter Infrared Auroral Mapper (JIRAM) experiment on board Juno has made spectroscopic observations of the trihydrogen cation (H3+) emissions in both northern and southern auroral regions (Dinelli et al., 2017; Adriani et al., 2017; Mura et al., 2017) and at mid-to-low latitudes (this paper). Observations targeting the limb of the planet from 60° North to 60° South latitudes were acquired with JIRAM's spectrometer in August 2016 and March 2017. We use these observations to characterize, for the first time, the vertical distribution of the H3+ emissions as a function of latitude across Jupiter's dayside. H3+ emission features in the 3-4 μm spectral band were used to retrieve the H3+ volume mixing ratio (VMR) and atmospheric temperatures as a function of altitude. The H3+ density profile has a quasi-symmetric distribution with latitude, decreasing from 5 × 104 cm-3 at 300 km to 2 × 103 cm-3 at 650 km altitude above the 1-bar level (column densities of 3.5 × 1012 cm-2 to 1.4 × 1011 cm-2, assuming a 700 km column depth). The H3+ VMR is higher in the Southern hemisphere than in the North with values at 500 km of 4 × 10-4 ppmv at 40°N and 8 × 10-4 ppmv at 40°S. Retrieved temperatures increase almost monotonically with increasing altitude, hovering around 400 K at 300 km and >900 K at about 700 km.

The exchange of energy and momentum between the Earth’s upper atmosphere and ionosphere, and its space environment (magnetosphere) is regulated by electric currents (called Birkeland currents) flowing along magnetic field lines that connect these two regions of space1. The associated electric currents flow towards and away from each pole primarily in two concentric conical sheets2. It has been expected that powerful sheets of magnetic-field-aligned electric currents would be found in association with the bright Jovian auroras3. The Juno spacecraft is well positioned to explore Jupiter’s polar magnetosphere and sample Birkeland or field-aligned currents and particle distributions. Since July 2016, Juno has maintained a near-polar orbit, passing over both polar regions every 53 days. From this vantage point, Juno’s complement of science instruments gathers in situ observations of magnetospheric particles and fields while its remote-sensing infrared and ultraviolet spectrographs and imagers map auroral emissions4. Here we present an extensive analysis of magnetic field perturbations measured during Juno’s transits of Jupiter’s polar regions, and thereby demonstrate Birkeland currents associated with Jupiter’s auroral emissions. We characterize the magnitude and spatial extent of the currents and we find that they are weaker than anticipated and filamentary in nature. A significant asymmetry is observed between the field perturbations and the current associated with the northern and the southern auroras. The Juno spacecraft’s observations of magnetic field perturbations in Jupiter’s polar regions show Birkeland currents associated with aurorae that are weaker than anticipated and filamentary in nature. An asymmetry is observed between the northern and southern auroras.

The Alfven wave mode transmits field‐aligned currents and large‐scale turbulence throughout Jupiter's magnetosphere. Magnetometer data from the Juno spacecraft have provided the first observations of Alfvenic fluctuations along the polar magnetic flux tubes connected to Jupiter's main auroral oval and the Jovian satellites. Transverse magnetic field perturbations associated with Io are observed up to ~90° away from main Io footprint, supporting the presence of extended Alfvenic wave activity throughout the Io footprint tail. Additional broadband fluctuations measured equatorward of the statistical auroral oval are composed of incompressible magnetic turbulence that maps to Jupiter's equatorial plasma sheet at radial distances within ~20 R(sub J). These fluctuations exhibit a k(sub ||) power spectrum consistent with strong magnetohydrodynamic turbulence. This turbulence can generate up to ~100 mW/m(exp 2) of Poynting flux to power the Jovian aurora in regions connected to the inner magnetosphere's central plasma sheet.

An edited version of this paper was published by AGU. Copyright 2019 American Geophysical Union.

The two main ultraviolet-signatures resulting from the Io-magnetosphere interaction are the local auroras on Io's atmosphere, and the Io footprints on Jupiter. We study here how Io's daily eclipses ...

In this study we performed a new analysis of ground-based observations that were taken on 17 April 2011 using the 10-metre Keck telescope on Mauna Kea, Hawaii. Emissions from H 3 + , a major ion in Saturn’s ionosphere, were previously analyzed from these observations, indicating that peaks in emission at specific latitudes were consistent with an influx of charged water products from the rings known as ‘ring rain’. Subsequent modeling showed that these peaks in emission are best explained by an increase in H 3 + density, rather than in column-averaged H 3 + temperatures, as a local reduction in electron density (due to charge exchange with water) lengthens the lifetime of H 3 + . However, what has been missing until now is a direct derivation of the H 3 + parameters temperature, density and radiative cooling rates, which are required to confirm and expand on existing models and theory. Here we present measurements of these H 3 + parameters for the first time in the non-auroral regions of Saturn, using two H 3 + lines, Q(1,0 − ) and R(2,2). We confirm that H 3 + density is enhanced near the expected ‘ring rain’ planetocentric latitudes near 45°N and 39°S. A low H 3 + density near 31°S, an expected prodigious source of water, may indicate that the rings are ‘overflowing’ material into the planet such that H 3 + destruction by charge-exchange with incoming neutrals outweighs its lengthened lifetime due to the aforementioned reduction in electron density. Derived H 3 + temperatures were low while the density was high at 39°S, potentially indicating that the ionosphere is most affected by ring rain in the deep ionosphere. Saturn’s moon Enceladus, a known water source, is connected with a dense region of H 3 + centered on 62°S, perhaps indicating that charged water from Enceladus is draining into Saturn’s southern mid-latitudes. We estimated the water product influx using previous modeling results, finding that 432 - 2870 kg s − 1 of water delivered to Saturn’s mid-latitudes is sufficient to explain the observed H 3 + densities. Assuming that our Saturn northern Spring measurement represents all seasons, and that the rings are able to reorganize over time, the ring rain mechanism alone will drain Saturn’s rings to the planet in 292 − 124 + 818 million years.

Source code for the PCD model is available at the website (https://github.com/gasgiant/jfield).

International audience; We report for the first time, simultaneous ion, electron, magnetic field vector and electric field wave measurements made possible by Mars Atmosphere and Volatile EvolutioN, during ion energy flux spikes in low-altitude radial crustal magnetic fields on the Mars dayside. Observations show energetic electrons and ions (E > 25 eV) precipitating on magnetic field lines assumed as closed. Ions (E < 1.4 keV) display broad velocity distributions toward Mars, showing ions flowing from higher altitude possibly after magnetic reconnection or loss cone filling from pitch angle scattering effects. Precipitating ions (E < 1.4 keV) show nonadiabatic features depending on ion mass and energy and returning ions (E < 1.4 keV) show evidence of conserving the first adiabatic invariant in a mirror field. We observe magnetic field perturbations up to 60 nT, electric field wave amplitudes up to 38 mV/m, and brief periods of peaked electron spectra. At ∼175 km and at times Mars Atmosphere and Volatile EvolutioN is below the mirroring altitude of electrons, we observe mirroring and transverse heating of H+ ions alongside increased electric field wave amplitude fluctuations. It suggests field aligned potential drops result from different mirror altitudes of ions and electrons. Ions E > 1.4 keV (O+) occur as injected accelerated ion beams and ions heated after energization or deceleration. Energy dispersed kilo-electron-volt ions suggest a selection effect in radial magnetic fields for lower-energy Marsward ions, compared to reflection of higher-energy anti-Sunward ions. Precipitating kilo-electron-volt ions show energy deposition rates of 3.6 ×10-6 W/m2 and sputtering escape rates from precipitating O+ ions of 1.5 ×105/(cm2.s) and 2.1 ×106/(cm2.s) are calculated.

International audience; In this work, we study the influence of the September 2017 solar event on the precipitating heavy ion fluxes towards Mars' atmosphere as seen by MAVEN/SWIA, an energy and angular ion spectrometer and by MAVEN/STATIC, an energy, mass and angular ion spectrometer. After a careful reconstruction of the background induced by the Solar Energetic Particle (SEP) event in the MAVEN/SWIA spectrometer, we investigate the precipitating ion flux responses to the space weather events that took place in September 2017. This period is a unique opportunity to analyze the respective role of various possible drivers of heavy ion precipitation into Mars’ atmosphere with a wide range of different space weather events occurring during the same month. This study shows an increase in the precipitation flux by more than one order of magnitude during the arrival of the September Interplanetary Coronal Mass Ejection (ICME) compared to the average flux during quiet solar conditions. We also showed that among the possible solar drivers, the solar wind dynamic pressure is the most significant during September 2017.