The Juno spacecraft continues to map the gas giant’s complex magnetic field with ever-increasing resolution in space and time, taking advantage of the natural evolution of Juno’s polar orbit and time on target. At the beginning of the prime mission in 2016, Juno’s cloud-topping periapsis occurred just northward of the equator. With each subsequent orbit, Juno’s perijove marches northward by ∼1°, owing to the apsidal precession of the orbit caused by Jupiter’s tidal bulge. Our recent spherical harmonic models derived from Juno measurements through orbit 66 of Extended Mission 1 (EM1, periJove at 56 degrees north latitude) routinely introduce a correction to the planet’s rotation period along with resolution of spherical harmonic coefficients corresponding to smaller spatial scales. Jupiter’s planetary rotation period (per IAU) has been determined with greater accuracy than that provided by observations of its radio emissions (System III (1965): 9h 55m 29.711s +/-0.04s). The secular variation of the magnetic field during Juno’s mission through orbit 66 (by ~0.122°/yr) yields an improved planetary rotation period of 9h 55m 29.697s, if the variation is attributed to the limited accuracy of the IAU adopted planetary rotation period. Much of the apparent motion of the Great Blue Spot (GBS), the localized patch of intense magnetic field near the equator, can be accounted for by inaccuracy of System III (1965). As Juno’s periJove migrates further northward in EM1 (through orbit 76) and EM2, the polar regions will be mapped at lower altitudes affording comparison with fluid motions such as those probed by Juno’s Microwave Radiometer (MWR). The latter half of EM1 orbits will complete mapping of the mid latitude high flux band, and EM2 will map the field with periJoves to 81 degrees north latitude where the circumpolar cyclones encircle the pole.

Intense upward electron beams were measured by the Juno JADE instrument in the northern hemisphere, low-latitude auroral zone source region. In this study we report on how these electron beams interact with plasma near and within the Jovian hectometric (HOM) emission (1 MHz < f < 5 MHz) source region. Within the source region large upward loss cones are observed in the northern polar region at radial distances of 2Rj, magnetic latitude of 70 degrees. Intense, narrow electron beams (E < 3 keV) are then observed, but within one second wave-particle scattering is observed, filling the loss cone to energies > 50 keV. These energies persist for several seconds before fading, leaving an empty loss cone again. The loss cone provides a free-energy source for HOM emission resulting from the cyclotron maser instability. We use quasilinear analysis to examine the generation of HOM and the dynamics of wave-particle interaction of the electron beams with HOM, and the generation via Landau interaction of whistler mode emission. The dynamic spectrum of the HOM emission generated by the loss-cone electrons as well as that of the low-frequency whistler-mode waves generated by the up-going electron beam can be constructed by quasilinear theory, which compare well with observation. The saturated state of the energetic electron velocity distribution function constructed via quasilinear theory also compare reasonably with observation.

High energy particle fluxes (>15MeV e- and 120MeV p+) throughout the Jovian magnetosphere have been continuously measured by the MAG investigation’s ASC instrument. Juno’s highly elliptical polar orbit has effectively traversed almost all of the Jovian magnetosphere with most regions sampled multiple times over time. Pronounced variations in the observed flux for comparable regions of the magnetosphere are observed in association with the positions of the Galilean moons and their associated dust and plasma tori, while global variations appear to be coupled to magnetic compression due to corona mass ejections. Oversampling of specific regions affords the opportunity to compile a quiet time map of the energetic trapped particle environment despite variations in solar activity and satellite-related effects. Subtracting this quiet time flux from that observed yields detailed information on the impact of solar activity, the Galilean moons, and the gossamer rings on the high-energy trapped particle environment of Jupiter. We present the observed quiet time map and show the impact on the trapped high-energy flux from the abovementioned local sources and sinks, and compare these results to those observed by Pioneer 10 and 11.

The magnetospheric cusp connects the planetary magnetic field to interplanetary space, offering opportunities for charged particles to precipitate to or escape from the planet. Terrestrial cusps are typically found near noon local time, but the characteristics of the Jovian cusp are unknown. Here for the first time we show direct evidence of Jovian cusps using datasets from multiple instruments onboard Juno spacecraft. We find that the cusps of Jupiter are in the dusk sector, which is contradicting Earth-based predictions of a near-noon location. Nevertheless, the characteristics of charged particles in the Jovian cusps resemble terrestrial and Saturnian cusps, implying similar cusp microphysics exist across different planets. These results demonstrate that while the basic physical processes may operate similarly to those at Earth, Jupiter’s rapid rotation and its location in the heliosphere can dramatically change the configuration of the cusp. This work provides significant insights into the fundamental consequences of star-planet interactions, highlighting how planetary environments and rotational dynamics influence magnetospheric structures.

The Juno Waves instrument can be used to accurately determine the electron density inside Io's orbit, the inner Io torus. These observations have revealed a local peak in the electron density just inside M = 5 and at centrifugal latitudes above about 10 degrees ${}<^>{\circ}$ that is likely the 'cold torus' as identified in Earth-based observations of S+ ${\mathrm{S}}<^>{+}$ emissions. This peak or "finger" is separated from the more dense Io torus by a local minimum or 'trough' at M >= ${\ge} $ 5. The electron densities are inferred by identifying characteristic frequencies of the plasma such as the low-frequency cutoff of Z-mode radiation at fL=0 ${f}_{L=0}$ and the low-frequency cutoff of ordinary mode radiation at fpe ${f}_{pe}$ that depend on the electron density. The "finger" density ranges from about 0.2 to 65 cm-3 ${\text{cm}}<^>{-3}$ and decreases with increasing centrifugal latitude. The "trough" densities range from 0.05 to similar to ${\sim} $10 cm-3 ${\text{cm}}<^>{-3}$. This pattern of a density "trough" followed by the "finger" closer to Jupiter is found on repeated passes through the inner Io torus over a range of centrifugal latitudes. Using a simple model for the electron densities measured above about 10 degrees ${}<^>{\circ}$ centrifugal latitude, we've estimated the scale height of the "finger" densities as about 1.17 RJ ${\mathrm{R}}_{J}$ with respect to the centrifugal equator, which is somewhat surprising given the expected cold temperature of the cold torus. The larger scale height suggests a population of light ions, such as protons, is elevated off the centrifugal equator. This is confirmed by a multi-species diffusive equilibrium model.

The Juno spacecraft, in extended mission, explores the environments of the Galilean satellites as it passes through Jupiter’s equator plane prior to periJove. Two close passages of Io with a minimum altitude of ~1500 km were targeted to occur on orbits 57 and 58, providing a wealth of information on Io’s interior (gravity), geologic processes, atmosphere, and interaction with Jupiter’s magnetosphere. Juno’s magnetometer investigation samples the vector magnetic field in Io’s vicinity at 64 samples/s. Here we discuss Io’s interaction with the Jovian magnetosphere and the detection of ion cyclotron waves at ~0.5 Hz, ~1 Hz, and ~2 Hz, associated with Io-genic SO2, S, and O.

Decametric radio emissions (DAM) originating in Jupiter’s polar aurorae ought to generate along magnetic field lines at the local electron gyrofrequency. The Io-related DAM have received particular attention since the 1980’s, and it is expected that the maximum frequency of these emissions is bounded by the maximum magnetic field strength near the footprint of the instantaneous Io Flux Tube. DAM have been observed from Earth and spacecraft flybys before Juno, limiting the observation geometry to equatorial latitudes. Since 2016, and thanks to Juno, we have been able to observe Io-related DAM from a wide range of latitudes, leading to the observation of a new DAM feature that we preliminarily called “butterfly”. We analyze the Waves data from May 2016 to June 2023 searching for these butterflies to catalog them and determine their relationship with Io and the Jovian magnetic field. Based on the observation geometries, we found that these events (˜ 135) are Io-related, they are always observed when Juno is in southern latitudes, they last for ˜5 hours and their maximum observed frequency is ˜20 MHz. As Juno is spending more time in southern latitudes as the mission progresses, the observation of butterflies keeps increasing over the years. Here, we study the role of the dipolar magnetic field of the southern hemisphere of Jupiter in the generation and observation of the butterfly events.

Jupiter’s ultraviolet (UV) polar auroral emissions are highly variable, both spatially and temporally. Observations over Jupiter’s northern and southern polar aurora during Juno’s prime mission did not reveal electron distributions with sufficient energy flux to produce the range of UV brightnesses (10s to 100s of kilorayleigh; kR) typically observed in that region. One suggestion was that significant electron acceleration was occurring below the altitudes sampled by Juno during that timeframe. Juno’s extended mission has provided an opportunity to test this hypothesis by accessing altitudes below 0.2 jovian radii (1 RJ = 71,492 km) above Jupiter’s northern polar auroral region. We present the characteristic features and energy flux of electron distributions at these low altitudes, primarily between 30 eV to 30 keV. A persistent feature below altitudes of 0.5 Rj is a low-energy cut-off in the electron distributions at a few 100s of eV. The energy flux in this energy range have maximum values of several 10s of mW/m-2, suggesting that contributions from electrons above 30 keV are likely required to account for the UV polar auroral emissions.

Jupiter's upper atmosphere is significantly hotter than expected based on the amount of solar heating it receives. This temperature discrepency is known as the 'energy crisis' due to it's nearly 50-year duration and the fact it also occurs at Saturn, Uranus and Neptune. At Jupiter, magnetosphere-ionosphere coupling gives rise to intense auroral emissions and enormous energy deposition in the magnetic polar regions, so it was presumed long ago that redistribution of this energy could heat the rest of the planet. However, most global circulation models have difficulty redistributing auroral energy globally due to the strong Coriolis forces and ion drag on this rapidly rotating planet. Consequently, other possible heat sources have continued to be studied, such as heating by gravity and acoustic waves emanating from the lower atmosphere. Each global heating mechanism would imprint a unique signature on global temperature gradients, thus revealing the dominant heat source, but these gradients have not been determined due a lack of planet-wide, high-resolution data. The last global map of Jovian upper-atmospheric temperatures was produced using ground-based data taken in 1993, in which the region between 45o latitude (north & south) and the poles was represented by just 2 pixels. As a result, those maps did not (or could not) show a clear temperature gradient, and furthermore, they even showed regions of hot atmosphere near the equator, supporting the idea of an equatorial heat source, e.g. gravity and/or acoustic wave heating. Therefore observationally and from a modeling perspective, a concensus has not been reached to date. Here we report new infrared spectroscopy of Jupiter's major upper-atmospheric ion H3+, with a spatial resolution of 2o longitude and latitude extending from pole to equator, capable of tracing the global temperature gradients. We find that temperatures decrease steadily from the auroral polar regions to the equator. Further, during a period of enhanced activity possibly driven by a solar wind compression, a high-temperature planetary-scale structure was observed which may be propagating from the aurora. These observations indicate that Jupiter's upper atmosphere is predominantly heated via the redistribution of auroral energy, and therefore that Coriolis forces and ion drag are observably overcome.

Energetic particle injections are commonly observed in Jupiter's magnetosphere and have important impacts on the radiation belts. We evaluate the roles of electron injections in the dynamics of whistler-mode waves and relativistic electrons using Juno measurements and wave-particle interaction modeling. The Juno spacecraft observed injected electron flux bursts at energies up to 300 keV at M shell similar to 11 near the magnetic equator during perijove-31. The electron injections are related to chorus wave bursts at 0.05-0.5 f(ce) frequencies, where f(ce) is the electron gyrofrequency. The electron pitch angle distributions are anisotropic, peaking near 90 degrees pitch angle, and the fluxes are high during injections. We calculate the whistler-mode wave growth rates using the observed electron distributions and linear theory. The frequency spectrum of the wave growth rate is consistent with that of the observed chorus magnetic intensity, suggesting that the observed electron injections provide free energy to generate whistler-mode chorus waves. We further use quasilinear theory to model the impacts of chorus waves on 0.1-10 MeV electrons. Our modeling shows that the chorus waves could cause the pitch angle scattering loss of electrons at <1 MeV energies and accelerate relativistic electrons at multiple MeV energies in Jupiter's outer radiation belt. The electron injections also provide an important seed population at several hundred keV energies to support the acceleration to higher energies. Our wave-particle interaction modeling demonstrates the energy flow from the electron injections to the relativistic electron population through the medium of whistler-mode waves in Jupiter's outer radiation belt.

Abstract The micro Advanced Stellar Compass is an attitude reference for the MAG investigation onboard Juno. The μASC camera head unit images the star field with a CCD that is also sensitive to particles with enough energy to pass through the camera shielding: >15 MeV electrons and >80 MeV protons. This provides the capability to monitor fluxes of high‐energy particles in Jupiter’s magnetosphere. A survey of energetic electron fluxes sampled during the first 47 Juno orbits reveals instances of variations observed when Juno is traversing the M‐shell of the Galilean moons. Juno's traversal of the Europa M‐shell often results in distinctly particle signatures. We present the μASC observations of increased electron flux during the crossing of Europa’s plasma wake, and depletion of energetic electron flux on the upstream side. The upstream/downstream differences indicate that the wake environment of Europa drives strong pitch angle scattering on relativistic electrons.

The magnetospheric cusp connects the planetary magnetic field to interplanetary space, offering opportunities for charged particles to precipitate to or escape from the planet. Terrestrial cusps are typically found near noon local time, but the characteristics of the Jovian cusp are unknown. Here we show direct evidence of Jovian cusps using datasets from multiple instruments onboard Juno spacecraft. We find that the cusps of Jupiter are in the dusk sector, which is contradicting Earth-based predictions of a near-noon location. Nevertheless, the characteristics of charged particles in the Jovian cusps resemble terrestrial and Saturnian cusps, implying similar cusp microphysics exist across different planets. These results demonstrate that while the basic physical processes may operate similarly to those at Earth, Jupiter's rapid rotation and its location in the heliosphere can dramatically change the configuration of the cusp. This work provides useful insights into the fundamental consequences of star-planet interactions, highlighting how planetary environments and rotational dynamics influence magnetospheric structures.

Jupiter's moon Europa contains a subsurface ocean whose presence is inferred from magnetic field measurements, the interpretation of which depends on knowledge of Europa's local plasma environment. A recent Juno spacecraft flyby returned new observations of plasma electrons with unprecedented resolution. Specifically, powerful magnetic field‐aligned electron beams were discovered near Europa. These beams, with energies from ∼30 to ∼300 eV, locally enhance electron‐impact‐excited emissions and ionization in Europa's atmosphere by more than a factor three over the local space environment, and are associated with large jumps of the magnetic fields. The beams therefore play an essential role in shaping Europa's plasma and magnetic field environment and thus need to be accounted for electromagnetic sounding of Europa's ocean and plume detection by future missions such as JUICE and Europa Clipper.

AbstractJupiter's poleward (Zone II) main aurora exhibits bi‐directional electron acceleration; upward acceleration dominates but downward acceleration generates strong aurora. During Juno's first perijove (PJ1), the upward acceleration manifested as narrow electron angular beams (within ∼5° of the magnetic field) over the 30–1,200 keV energy range of Juno's Jupiter Energetic Particle Detector Investigation (JEDI). These beams can be simply connected (non‐uniquely) to >10 to perhaps 100's of MeV electrons that penetrated the radiation shielding of the camera head of the Magnetometer Investigation's Advanced Stellar Compass (ASC). The most intense of those multiple MeV populations are shown to have been highly directional and propagating upwards. How auroral processes generate such beams is unknown. With azimuthal symmetry assumed (not demonstrated here), these beams provided >1026 s−1 of >30 keV electrons to Jupiter's vast magnetosphere, a possibly critical and dominating source of energetic electrons to that region and ultimately to Jupiter's radiation belts.

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.

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.

On June 7, 2021 Juno performed a close flyby of Ganymede, providing a unique opportunity to improve the current understanding of the magnetosphere. Here, we study the high-resolution (64 Hz signal) magnetic field spectrum employing three different approaches: 1) analysis of a ~3.5 minute near Juno’s closest flyby to the moon, 2) analysis of 12 sliding windows of ~2 min in this period and, and 3) analysis of a ~63 s window selected based on the dominant frequencies observed in the evolutionary spectra of the entire flyby. A fundamental period of ~16 s is observed in all three methods. In the specific case of the spectrum of the 63 s window, this shows a harmonic structure which could potentially be related to the frequencies associated with resonances of a dipole field. If this were the case, we estimate that the plasma density near the equator at 1.685 RG (selected L-shell) is equal to 22 amu/cm3, a much lower value than the local density of the plasma sheet near Ganymede (~100 amu/cm3). These two aspects may indicate that Juno crossed closed magnetic field lines of Ganymede’s magnetosphere for a short period of time only, if at all.

A star camera aboard the Juno spacecraft traveling from Earth to Jupiter serendipitously recorded the impact of interplanetary dust particles (IDPs) by imaging bits of the spacecraft ejected from the IDP impact sites. In essence, the Juno spacecraft, with its expansive ~60 m2 of solar arrays, served as a dust detector with orders of magnitude more aperture than dedicated dust detectors specifically designed and flown to detect dust impacts. Consequently, Juno recorded many impacts with the larger (few to tens of micro-meters) and less numerous IDPs that populate the inner solar system, establishing for the first time their distribution and source (Jorgensen et al., 2020). Six months prior to its arrival at Jupiter, the Juno spacecraft recorded a singular burst of interplanetary dust particle impacts attributed to passage through the extended tail of a comet. That comet has now been identified as the recently discovered Jupiter family comet P/2019 S3 Pan-STARRS (SPKID 1003641), affording a unique opportunity to characterize the dynamical motion of the comet’s dust tail. Dust impacting the spacecraft orbits under the influence of radiation pressure forces and gravity (ratio b = ~0.05), escaping the comet nucleus ~2 years prior to impact on the spacecraft and ~1 year post comet perihelion. Impacting dust, with an implied radius of ~10 mm, escaped the comet nucleus with a radial velocity of ~120 ms-1, appropriate to a comet with a radius of a few km.

Juno's highly elliptical polar orbits provide unprecedented in-situ observations of the electrodynamic interaction between Jupiter and its volcanic moon Io. These observations occur in regions never sampled before both near Io's orbit and near Jupiter's ionosphere and at distances between the two. Magnetic field data obtained during multiple traversals of magnetic field lines mapping to Io's orbit reveal remarkably rich and complex magnetic signatures near flux tubes connected to Io's orbital position. Here we present a methodology to model the distribution of currents along Io's flux tube (IFT) and Alfv & eacute;n wings in such a way as to match the magnetic field signature observed during Juno's traversals of the IFT and Alfv & eacute;n wings downstream of Io. We obtain the location, size and morphology of the current-carrying region as well as the distribution of currents within the IFT and Alfv & eacute;n wings. The observed field-aligned currents exhibit strong filamentation, with upward and downward currents splitting into secondary cells rather than forming uniform structures. Additionally, there is a strong correlation between total field-aligned current intensity, particle energy flux, and Poynting flux, indicating efficient energy transfer and coupling in the Jupiter-Io system. Using all of Juno's traversals up to perijove (PJ) pass 42, we estimate the strength of the interaction with regards to distance along Io's extended tail, Io's position in the plasma torus and the magnetic field intensity at the footprint in Jupiter's ionosphere, illuminating the interaction of Jovian magnetospheric plasma with Io and setting important constraints in the Io-Jupiter interaction.

Abstract On days 2023‐364 and 2024‐034, the Juno spacecraft made close passages of Jupiter's moon Io, at altitudes of about 1,500 km. Data obtained from the first flyby, when the spacecraft was on magnetic field lines connected to both Jupiter and Io, revealed deep flux decreases. In addition, Juno's energetic particle detectors observed tens to hundreds of keV electron and proton beams. Such beams could be generated near Jupiter on field lines associated with Io. The second encounter occurred in the plasma wake and a more modest flux decrease was observed. Furthermore, data from both encounters suggest a spatially extensive decrease in >1 MeV electrons that includes regions inward of Io's orbit. In the immediate vicinity of Io, signatures of absorption likely dominate the data whereas diffusion and wave‐particle interactions are expected to be needed to understand MeV electron data in the wider spatial region around Io.