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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.

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.

The UVS instrument on the Juno mission recorded transient bright emission from a point source in Jupiter's atmosphere. The spectrum shows that the emission is consistent with a 9600-K blackbody located 225 km above the 1-bar level and the duration of the emission was between 17 ms and 150 s. These characteristics are consistent with a bolide in Jupiter's atmosphere. Based on the energy emitted, we estimate that the impactor had a mass of 250-5000 kg, which corresponds to a diameter of 1-4 m. By considering all observations made with Juno UVS over the first 27 perijoves of the mission, we estimate an impact flux rate of 24,000 per year for impactors with masses greater than 250-5000 kg., Comment: Accepted in GRL. 21 pages, 3 figures

11 transient bright flashes were detected in Jupiter's atmosphere using the UVS instrument on the Juno spacecraft. These bright flashes are only observed in a single spin of the spacecraft and their brightness decays exponentially with time, with a duration of ~1.4 ms. The spectra are dominated by H2 Lyman band emission and based on the level of atmospheric absorption, we estimate a source altitude of 260 km above the 1-bar level. Based on these characteristics, we suggest that these are observations of Transient Luminous Events (TLEs) in Jupiter's upper atmosphere. In particular, we suggest that these are elves, sprites or sprite halos, three types of TLEs that occur in the Earth's upper atmosphere in response to tropospheric lightning strikes. This is supported by visible light imaging, which shows cloud features typical of lightning source regions at the locations of several of the bright flashes. TLEs have previously only been observed on Earth, although theoretical and experimental work has predicted that they should also be present on Jupiter., Comment: Accepted in JGR: Planets. 28 pages, 8 figures

Jupiter displays many distinct auroral structures, among which auroral dawn storms and auroral injections are often observed contemporaneously. However, it is unclear if the contemporaneous nature of the observations is a coincidence or part of an underlying physical connection. We show six clear examples from a recent Hubble Space Telescope campaign (GO‐14634) that each display both auroral dawn storms and auroral injection signatures. We found that these conjugate phenomena could exist during intervals of either relatively low or high auroral activity, as evidenced by the varied levels of total auroral power. In situ observations of the magnetosphere by Juno show a strong magnetic reconnection event inside of 45 Jupiter radii (RJ) on the predawn sector, followed by two dipolarization events within the following 2 hr, coincident with the auroral dawn storm and auroral injection event. We therefore suggest that the auroral dawn storm is the manifestation of magnetic reconnection in the dawnside magnetosphere. The dipolarization region is mapped to the auroral injection, strongly suggesting that this was associated with the auroral injection. Since magnetic reconnection and dipolarization are physically connected, we therefore suggest that the often‐conjugate auroral dawn storm and auroral injection events are also physically connected consequences.

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

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.

The Jovian magnetosphere assumes a disc‐like geometrical configuration (“magnetodisc”) owing to the persistent presence of a system of azimuthal currents circulating in a washer‐shaped volume aligned with, or near, the magnetic equatorial plane. A Voyager era empirical model of the magnetodisc is fitted to vector magnetic field measurements obtained during the Juno spacecraft's first 24 orbits. The best fitting (within 30 Jovian radii) magnetodisc model is characterized by an inner and outer radius of 7.8 and 51.4 Jovian radii, a half‐thickness of 3.6 Jovian radii, with a surface normal at 9.3° from the Jovigraphic pole and 204.2° System 3 west longitude. We supplement the magnetodisc model with a second current system, also confined to the magnetic equatorial plane, consisting of outward radial currents that presumably effect the transfer of angular momentum to outward flowing plasma. Allowing for variation of the magnetodisc's azimuthal and radial current systems from one 53‐day orbit to the next, we develop an index of magnetospheric activity that may be useful in interpretation of variations in auroral observations., Key Points An empirical magnetodisc model is fitted to the Juno magnetic field observationsThe magnetodisc model provides a more accurate representation of the magnetic field in the inner and middle magnetosphere of JupiterThe model is independently tested via observations of charged particle interactions with the Jovian satellites

The Juno spacecraft crossed flux tubes connected to the Io footprint tail at low Jovian altitudes on multiple occasions. The transits covered longitudinal separations of approximately 10 degrees to 120 degrees along the footprint tail. Juno's suite of magnetospheric instruments acquired detailed measurements of the Io footprint tail. Juno observed planetward electron energy fluxes of similar to 70mW/m(2) near the Io footprint and similar to 10mW/m(2) farther down the tail, along with correlated, intense electric and magnetic wave signatures, which also decreased down the tail. All observed electron distributions were broad in energy, suggesting a dominantly broadband acceleration process, and did not show any broad inverted-V structure that would be indicative of acceleration by a quasi-static, discrete, parallel potential. Observed waves were primarily below the proton cyclotron frequency, yet identification of a definitive wave mode is elusive. Beyond 40 degrees down the footprint tail, Juno observed depleted upward loss cones, suggesting that the broadband acceleration occurred at distances beyond Juno's transit distance of 1.3 to 1.7R(J). For all transits, Juno observed fine structure on scales of approximately tens of kilometers and confirmed independently with electron and wave measurements that a bifurcated tail can intermittently exist. Plain Language Summary The Juno spacecraft crossed regions magnetically connected to auroral structures associated with Jupiter's moon Io on multiple occasions. The transits covered longitudinal separations of approximately 10 degrees to 120 degrees along Io's auroral tail. Juno's suite of instruments acquired detailed measurements of these auroral structures. Juno directly observed the electrons that sustain these auroral features before they crash into the atmosphere and generate the brilliant aurora. The flux of these electrons decreased as Juno transited the tail farther from Io's longitude. While there are two main explanations for Io's auroral signatures, the nature of the observed electrons in this work favors one mechanism over the other. When Juno was far from Io's longitude, the observations suggest that the spacecraft was below the point at which the electrons are accelerated into the atmosphere. For all transits, Juno observed fine structure on scales of approximately tens of kilometers and confirmed that a bifurcated tail can intermittently exist.

In two previous papers (Dubinin et al., 2016, 2017a) we studied the influence of the crustal magnetic field and solar irradiance on the upper ionosphere of Mars based on the observations made on Mars Express. Here we discuss effects of solar wind and the interplanetary magnetic field using the MAVEN observations. It is shown that the upper ionosphere at solar zenith angles ≥ ∼ 40 o and altitudes above ∼ 350 − 400 km is asymmetrical along the direction of the motional electric field. In the hemisphere, in which the motional electric field is directed toward the planet, the ionosphere is denser and expands to higher altitudes as compared to the ionosphere in the opposite hemisphere. The difference in the density of O + and O 2 + ions in both hemispheres achieves almost one order. Such a difference arises due to a different ion convection. Ion convection in both ionospheres occurs in the same direction as the motion of the shocked solar wind in the adjacent magnetosheath although with very different velocities. The upper ionosphere is also sensitive to the variations in the solar wind dynamic pressure, solar wind flux and the value of the motional electric field with a distinct depletion at altitudes above ∼ 450 − 500 km with increase of these solar wind characteristics. The depletion is accompanied by an increase in the horizontal ion velocities. As a result, the ion fluxes to the tail only insignificantly vary with the modest variations of the solar wind characteristics.

A complex boundary layer with a variety of charged particle and electromagnetic field signatures, including a transition between plasma predominantly of solar wind origin and plasma of planetary origin, lies between the Martian bow shock and the ionosphere. In this paper, we develop and utilize algorithms to autonomously identify and characterize this ion composition boundary (ICB), using data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. We find an asymmetric ICB with a larger average thickness, lower altitude, and lower velocity shear in the hemisphere where the solar wind motional electric field points outward, as a result of the asymmetry of the mass loading process. The ICB thickness scales with the magnetosheath proton gyroradius at the top of the boundary layer but does not clearly vary with external drivers. The ICB location varies with solar wind ram pressure and crustal magnetic field strength, but does not clearly respond to solar wind Mach number or extreme ultraviolet irradiance. The ICB represents a distinct boundary for ion density and flow speed, but the magnetic field strength and direction typically do not vary significantly across the ICB. The plasma density and flow speed at the ICB vary seasonally, likely in response to variations in the neutral exosphere and/or atmosphere. However, the ICB on average remains at or below the altitude where pressure balance is achieved between the piled up magnetic field (MPB) and the solar wind ram pressure, regardless of season or crustal magnetic field strength.

The UltraViolet Spectrograph (UVS) and the Jupiter InfraRed Auroral Mapper (JIRAM) observed the north polar aurora before the first perijove of the Juno orbit (PJ1) on 27 August 2016. The UVS bandpass corresponds to the H2 Lyman and Werner bands that are directly excited by collisions of auroral electrons with molecular hydrogen. The spectral window of the JIRAM L-band imager includes some of the brightest H3+ thermal features between 3.3 and 3.6 μm. A series of spatial scans obtained with JIRAM every 30 s is used to build up five quasi-global images, each covering ∼12 min. of observations. JIRAM's best spatial resolution was on the order of 50 km/pixel during this time frame, while UVS has a resolution of about 750 km. Most of the observed large-scale auroral features are similar in the two spectral regions, but important differences are also observed in their morphology and relative intensity. Only a part of the UV-IR differences stems from the higher spatial resolution of JIRAM, as some of them are still present following smoothing of the JIRAM images at the UVS resolution. For example, the JIRAM images show persistent narrow arc structures in the 100°-180° SIII longitude sector at dusk not resolved in the ultraviolet, but consistent with the structure of in situ electron precipitation measured two hours later. The comparison between the H2 intensity and the H3+ radiance measured along two radial cuts from the center of the main emission illustrates the complex relation between the electron energy input, their characteristic energy and the H3+ emission. Low values of the H3+ intensity relative to the H2 brightness are observed in regions of high FUV color ratio corresponding to harder electron precipitation. The rapid loss of H3+ ions reacting with methane near and below the homopause appears to play a significant role in the control of the relative brightness of the two emissions. Cooling of the auroral thermosphere by H3+ radiation is spatially variable relative to the direct particle heating resulting from the precipitated electron flux.

Electrical currents in atmospheric lightning strokes generate impulsive radio waves in a broad range of frequencies, called atmospherics. These waves can be modified by their passage through the plasma environment of a planet into the form of dispersed whistlers1. In the Io plasma torus around Jupiter, Voyager 1 detected whistlers as several-seconds-long slowly falling tones at audible frequencies2. These measurements were the first evidence of lightning at Jupiter. Subsequently, Jovian lightning was observed by optical cameras on board several spacecraft in the form of localized flashes of light3–7. Here, we show measurements by the Waves instrument8 on board the Juno spacecraft9–11 that indicate observations of Jovian rapid whistlers: a form of dispersed atmospherics at extremely short timescales of several milliseconds to several tens of milliseconds. On the basis of these measurements, we report over 1,600 lightning detections, the largest set obtained to date. The data were acquired during close approaches to Jupiter between August 2016 and September 2017, at radial distances below 5 Jovian radii. We detected up to four lightning strokes per second, similar to rates in thunderstorms on Earth12 and six times the peak rates from the Voyager 1 observations13. The Waves instrument on board the Juno spacecraft has detected ~1,600 lightning strokes in roughly 1 year of close approaches to Jupiter, indicated by low-dispersion rapid whistlers much shorter than those detected by Voyager 1 in Io’s plasma torus.

Measurements provided by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft are analyzed to investigate the Martian magnetotail configuration as a function of interplanetary magnetic field (IMF) BY. We find that the magnetotail lobes exhibit a ~45deg twist, either clockwise or counterclockwise from the ecliptic plane, up to a few Mars radii downstream. Moreover, the associated cross-tail current sheet is rotated away from the expected location for a Venus-like induced magnetotail based on nominal IMF draping. Data-model comparisons using magnetohydrodynamic simulations are in good agreement with the observed tail twist. Model field line tracings indicate that a majority of the twisted tail lobes are composed of open field lines, surrounded by draped IMF. We infer that dayside magnetic reconnection between the crustal fields and draped IMF creates these open fields and may be responsible for the twisted tail configuration, similar to what is observed at Earth.

Mars Atmosphere and Volatile EvolutioN (MAVEN) mission observations show clear evidence of the occurrence of the magnetic reconnection process in the Martian plasma tail. In this study, we use soph ...

International audience; The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft arrived at Mars with the goal of determining the rates and mechanisms of atmospheric escape. Thermal hydrogen and hot oxygen escape are the two most important escape processes currently at work. Direct measurement of the escaping neutral hydrogen and oxygen atoms is impossible with current technology due to the low density and energy of escaping neutrals. However, when ionized and picked up by the solar wind, these escaping atoms can be detected by three particle detectors onboard MAVEN. By back-tracing the trajectories of measured pickup ions, constraints can be placed on the density of neutrals at altitudes not accessible by other measurement methods. In this work, pickup H+ and O+ data from the Solar Energetic Particle (SEP), Solar Wind Ion Analyzer (SWIA), and SupraThermal and Thermal Ion Composition (STATIC) instruments are used to assess the variability of neutral H and O exospheres at Mars. From an analysis of 2.5 Earth years of MAVEN data, we show that a strong H escape seasonal dependence is observed by SWIA and STATIC with inferred H escape rates as low as 3 × 1025 s-1 near aphelion and as high as 4 × 1026 s-1 near perihelion. Hot O escape rates derived from SEP, SWIA, and STATIC data imply a much less variable hot O exosphere with escape rates fluctuating by a factor of 2 around a mean value of 9 × 1025 s-1. Both escape rates are in general agreement with the most recent theoretical, modeled, and observationally inferred rates.

International audience; The precipitation of suprathermal electrons is the dominant external source of energy deposition and ionization in the Martian nightside upper atmosphere and ionosphere. We investigate the spatial patterns and variability of ionizing electrons from 115 to 600 km altitude on the Martian nightside, using CO2 electron impact ionization frequency (EIIF) as our metric, examining more than 3 years of data collected in situ by the Mars Atmosphere and Volatile EvolutioN spacecraft. We characterize the behavior of EIIF with respect to altitude, solar zenith angle, solar wind pressure, and the geometry and strength of crustal magnetic fields. EIIF has a complex and correlated dependence on these factors, but we find that it generally increases with altitude and solar wind pressure, decreases with crustal magnetic field strength and does not depend detectably on solar zenith angle past 115°. The dependence is governed by (a) energy degradation and backscatter by collisions with atmospheric neutrals below 220 km and (b) magnetic field topology that permits or retards electron access to certain regions. This field topology is dynamic and varies with solar wind conditions, allowing greater electron access at higher altitudes where crustal fields are weaker and also for higher solar wind pressures, which result in stronger draped magnetic fields that push closed crustal magnetic field loops to lower altitudes. This multidimensional electron flux behavior can in the future be parameterized in an empirical model for use as input to global simulations of the nightside upper atmosphere, which currently do not account for this important source of energy.

A spherical harmonic model of the magnetic field of Jupiter is obtained from vector magnetic field observations acquired by the Juno spacecraft during its first nine polar orbits about the planet. Observations acquired during eight of these orbits provide the first truly global coverage of Jupiter's magnetic field with a coarse longitudinal separation of ~45 deg between perijoves. The magnetic field is represented with a degree 20 spherical harmonic model for the planetary ("internal") field, combined with a simple model of the magnetodisc for the field ("external") due to distributed magnetospheric currents. Partial solution of the underdetermined inverse problem using generalized inverse techniques yields a model ("Juno Reference Model through Perijove 9") of the planetary magnetic field with spherical harmonic coefficients well determined through degree and order 10, providing the first detailed view of a planetary dynamo beyond Earth.

International audience; Jupiter’s atmosphere is rotating differentially, with zones and belts rotating at speeds that differ by up to 100 metres per second. Whether this is also true of the gas giant’s interior has been unknown1,2, limiting our ability to probe the structure and composition of the planet3,4. The discovery by the Juno spacecraft that Jupiter’s gravity field is north–south asymmetric5 and the determination of its non-zero odd gravitational harmonics J3, J5, J7 and J9 demonstrates that the observed zonal cloud flow must persist to a depth of about 3,000 kilometres from the cloud tops6. Here we report an analysis of Jupiter’s even gravitational harmonics J4, J6, J8 and J10 as observed by Juno5 and compared to the predictions of interior models. We find that the deep interior of the planet rotates nearly as a rigid body, with differential rotation decreasing by at least an order of magnitude compared to the atmosphere. Moreover, we find that the atmospheric zonal flow extends to more than 2,000 kilometres and to less than 3,500 kilometres, making it fully consistent with the constraints obtained independently from the odd gravitational harmonics. This depth corresponds to the point at which the electric conductivity becomes large and magnetic drag should suppress differential rotation7. Given that electric conductivity is dependent on planetary mass, we expect the outer, differentially rotating region to be at least three times deeper in Saturn and to be shallower in massive giant planets and brown dwarfs.

Juno is a PI-led mission to Jupiter, the second mission in NASA’s New Frontiers Program. The 3625-kg spacecraft spins at 2 rpm and is powered by three 9-meter-long solar arrays that provide ∼500 watts in orbit about Jupiter. Juno carries eight science instruments that perform nine science investigations (radio science utilizes the communications antenna). Juno’s science objectives target Jupiter’s origin, interior, and atmosphere, and include an investigation of Jupiter’s polar magnetosphere and luminous aurora.

In a two-week period between February and March of 2015, a series of interplanetary coronal mass ejections (ICMEs) and solar energetic particle (SEP) events encountered Mars. The interactions were observed by several spacecraft, including Mars Express (MEX), Mars Atmosphere and Volatile Evolution Mission (MAVEN), and Mars Odyssey (MO). The ICME disturbances were characterized by an increase in ion speed, plasma temperature, magnetic field magnitude, and energetic electron flux. Furthermore, increased solar wind density and speeds, as well as unusually high local electron densities and high flow velocities were detected on the nightside at high altitudes during the March 8 event. These effects are thought to be due to the transport of ionospheric plasma away from Mars. In the deep nightside, the peak ionospheric electron density at the periapsis of MEX shows a substantial increase, reaching number densities about 2.7 × 104 cm−3 during the second ICME in the deep nightside. This corresponds to an increase in the MO High-Energy Neutron Detector flux suggesting an increase in the ionization of the neutral atmosphere due to the high intensity of charged particles. Measurements of the SEP fluxs show a substantial enhancement before the shock of a fourth ICME causing impact ionization and absorption of the surface echo intensity which drops to the noise levels, below 10−15 V2m−2 Hz−1 from values of about 2 × 10−14 V2m−2 Hz−1. Moreover, the peak ionospheric density exhibits a discrete enhancement over a period of about 30 h around the same location, which may be due to impact ionization. Ion escape rates at this time are estimated to be in the order of 1025 to 1026 s−1.

Recent results of the first ever orbit through Jupiter's auroral region by NASA's Juno spacecraft did not show evidence of coherent acceleration in the auroral or polar region. However, in this letter, we show energetic particle data from Juno's Jupiter Energetic-particle Detector Instrument instrument during the third auroral pass that exhibits conclusive evidence of downward parallel electric fields in portions of Jupiter's polar region. The energetic particle distributions show inverted-V ion and electron structures in a downward electric current region with accelerated peaked distributions in hundreds of keV to ~1 MeV range. The origin of these large electric potential structures is investigated and discussed within the current theoretical framework of current-voltage relationships at both Earth and Jupiter. Parallel electric fields responsible for accelerating particles to maintain the aurora/magnetospheric circuit appear to be a common phenomenon among strongly magnetized planets with conducting ionospheres; however, their origin and generation mechanisms are subjects of ongoing research.

Since August 2016, measurements of Jupiter's microwave emissions at six wavelengths ranging from 1.3 cm to 50 cm have been made with the Juno Microwave Radiometer (MWR). In this paper, we introduce the first systematic set of in-situ observations of synchrotron radiation in a polar plane while describing the modeling approach we use to analyze this data (collected August 27th, 2016). Time series of brightness profiles at all six frequencies present similarities that are explained by the presence of known regions of intense synchrotron radiation. Our model predictions, though limited for now to the total intensity of the radiation, reproduce (qualitatively) the observation of temporal variations and allow to disentangle the synchrotron emission from the atmospheric emission. The discrepancies seen between the data and simulations confirm that physical conditions close to Jupiter affecting synchrotron emission (electron energy spectra, pitch-angle distributions, and the magnetic environment) are different than we anticipated.

Simultaneous operation of two Mars satellites, equipped with instruments for the study of the plasma environment close to Mars, the European satellite Mars Express and American satellite MAVEN, allows one to investigate the influence of the interplanetary environment on the Martian magnetosphere and atmospheric losses, induced by the solar wind, for the first time, with a sufficient degree of confidence. In this paper, the data from measurements on the Mars Express satellite (MEX) of heavy ion losses are analyzed in comparison with the solar wind and magnetic field measurements on the MAVEN satellite. The main issue is the spatial structure of the escaping ion flux and the influence of the nonstationarity of the solar wind flux on the escape rate.

The process that generates Earth’s most intense aurora is found to occur at Jupiter, but is of only secondary importance in generating Jupiter’s much more powerful aurora. The most intense aurora on Earth are generated by a 'discrete' process whereby electrons are accelerated coherently. Weaker aurora arise from wave scattering of magnetically trapped electrons. As Jupiter's aurora is orders of magnitude more powerful than Earth's, it was naturally assumed that the former process was responsible, yet early in situ observations by the Juno spacecraft found no evidence of the discrete process. Barry Mauk and collaborators report discrete downward accelerations of electrons on some auroral crossings, but the energy flux is much less than that caused by broadband processes, with broadband characteristics that are very different from those at Earth. The most intense auroral emissions from Earth’s polar regions, called discrete for their sharply defined spatial configurations, are generated by a process involving coherent acceleration of electrons by slowly evolving, powerful electric fields directed along the magnetic field lines that connect Earth’s space environment to its polar regions1,2. In contrast, Earth’s less intense auroras are generally caused by wave scattering of magnetically trapped populations of hot electrons (in the case of diffuse aurora) or by the turbulent or stochastic downward acceleration of electrons along magnetic field lines by waves during transitory periods (in the case of broadband or Alfvenic aurora)3,4. Jupiter’s relatively steady main aurora has a power density that is so much larger than Earth’s that it has been taken for granted that it must be generated primarily by the discrete auroral process5,6,7. However, preliminary in situ measurements of Jupiter’s auroral regions yielded no evidence of such a process8,9,10. Here we report observations of distinct, high-energy, downward, discrete electron acceleration in Jupiter’s auroral polar regions. We also infer upward magnetic-field-aligned electric potentials of up to 400 kiloelectronvolts, an order of magnitude larger than the largest potentials observed at Earth11. Despite the magnitude of these upward electric potentials and the expectations from observations at Earth, the downward energy flux from discrete acceleration is less at Jupiter than that caused by broadband or stochastic processes, with broadband and stochastic characteristics that are substantially different from those at Earth.

A Hot Flow Anomaly (HFA) is created when an interplanetary current sheet interacts with a planetary bow shock. Previous studies have reported observing HFAs at Earth, Mercury, Venus, Mars and Saturn. During Juno's approach to Jupiter, a number of its instruments operated in the solar wind. Prior to crossing into Jupiter's magnetosphere, Juno observed an HFA at Jupiter for the first time. This Jovian HFA shares most of the characteristics of HFAs seen at other planets. The notable exception is that the Jovian HFA is significantly larger than any HFA seen before. With an apparent size greater than 2 × 106 km the Jovian HFA is orders of magnitude larger than those seen at the other planets. By comparing the size of the HFAs at the other planets with the Jovian HFA, we conclude that HFAs size scales with the size of planetary bow shocks that the interplanetary current sheet interacts with.

We present the first comparison of Jupiter's auroral morphology with an extended, continuous and complete set of near-Jupiter interplanetary data, revealing the response of Jupiter's auroras to the interplanetary conditions. We show that for ∼1-3 days following compression region onset the planet's main emission brightened. A duskside poleward region also brightened during compressions, as well as during shallow rarefaction conditions at the start of the program. The power emitted from the noon active region did not exhibit dependence on any interplanetary parameter, though the morphology typically differed between rarefactions and compressions. The auroras equatorward of the main emission brightened over ∼10 days following an interval of increased volcanic activity on Io. These results show that the dependence of Jupiter's magnetosphere and auroras on the interplanetary conditions are more diverse than previously thought.

International audience; For the first time at Mars the statistical distribution of (1-D) electric field wave power in the magnetosphere is presented, along with the distribution of magnetic field wave power, as observed by the Mars Atmosphere and Volatile EvolutioN spacecraft from the first 14.5 months of the mission. Wave power in several different frequency bands was investigated, and the strongest wave powers were observed at the lowest frequencies. The presented statistical studies suggest that the full thermalization of ions within the magnetosheath does not appear to occur, as has been predicted by previous studies. Manual inspection of 140 periapsis passes on the dayside shows that Poynting fluxes (at 2-16 Hz) between ∼10-11 and 10-8 Wm-2 reach the upper ionosphere for all 140 cases. Wave power is not observed in the ionosphere for integrated electron densities greater than 1010.8 cm-2, corresponding to typical depths of 100-200 km. The observations presented support previous suggestions that energy from the Mars-solar wind interaction can propagate into the upper ionosphere and may provide an ionospheric heating source. Upstream of the shock, the orientation of the solar wind interplanetary magnetic field was shown to significantly affect the statistical distribution of wave power, based on whether the spacecraft was likely magnetically connected to the shock or not—something that is predicted but has not been quantitatively shown at Mars before. In flight performance and caveats of the Langmuir Probe and Waves electric field power spectra are also discussed.

We investigate the structure of Jupiter's dawnside magnetopause using observations obtained by particle and fields instrumentation on the Juno spacecraft. Characterization of Jupiter's magnetopause is critical for the understanding of mass and energy transport between the solar wind and the magnetosphere. We find an extended magnetopause boundary layer (MPBL) during a magnetopause crossing on 14 July 2016. This thick MPBL, in combination with a large magnetic field component normal to the magnetopause boundary, suggests that strong magnetospheric compression enhances mass transport across the magnetopause via magnetic reconnection. We further identify ~2 h increases in the total magnetospheric pressure adjacent to the magnetopause on 14 July 2016 and 1 August 2016. These large-scale structures provide evidence of focused energy transport into the magnetosphere via magnetohydrodynamic structures.

Jupiter's main auroral oval provides a window into the complex magnetospheric dynamics of the jovian system. The Juno spacecraft entered orbit about Jupiter on 5 July 2016 and carries onboard the Auroral Distributions Experiment (JADE) that can directly sample the auroral plasma structures. Here, we identify five distinct regimes in the JADE data based on composition/energy boundaries and magnetic field mappings, which exhibit considerable symmetry between the northern and southern passes. These intervals correspond to periods when Juno was connected to the Io torus, inner plasma sheet, middle plasma sheet, outer plasma sheet, and the polar region. When connected to the torus and inner plasma sheet, the heavy ions are consistent with a corotating pickup population. For Juno's first perijove, we do not find evidence for a broad auroral acceleration region at Jupiter's main auroral oval for energies below 100 keV.

With the aid of the radio and plasma wave (Waves) instrument onboard the Juno spacecraft, the first scientific close encounter to Jupiter (Perijove 1) of Juno led to an opportunity to perform direction finding measurements of the intense Jovian broadband kilometric (bKOM) radiation at 10 to 142 kHz, two escaping continuum radiation (ECR) events at 9 to 22 kHz, and two narrowband kilometric (nKOM) radiation events at 45–112 kHz. We conclude that the northern bKOM radio sources are localized on M-shell=50–60 field lines where M-shell is similar to L-shell for non-dipolar fields. The beam cone half-angle varies from 40∘ to 55∘. By intersecting the wave k vector with the Jovian centrifugal equator, two ECR sources are located inside and outside of 11–12 RJ, and two nKOM sources are found between 11 and 20 RJ. These source frequencies and locations can be used for plasma diagnostics in Jupiter's inner magnetosphere.

After a successful orbit insertion, the Juno spacecraft completed its first 53.5-day orbit and entered a very low altitude perijove with the full scientific payload operational for the first time on 27 August 2016. The Jupiter Energetic particle Detector Instrument measured ions and electrons over the auroral regions and through closest approach, with ions measured from ~0.01 to > 10 MeV, depending on species. This report focuses on the composition of the energetic ions observed during the first perijove of the Juno mission. Of particular interest are the ions that precipitate from the magnetosphere onto the polar atmosphere, and ions that are accelerated locally by Jupiter's powerful auroral processes. We report preliminary findings on the spatial variations, species, including energy and pitch angle distributions throughout the prime science region during the first orbit of the Juno mission. The prime motivation for this work was to examine the heavy ions that are thought to be responsible for the observed polar x-rays. JEDI did observe precipitating heavy ions with energies >10 MeV, but for this perijove the intensities were far below those needed to account for previously observed polar x-ray emissions. During this survey we also found an unusual signal of ions between oxygen and sulfur. We include here a report on what appears to be a transitory observation of magnesium, or possibly sodium, at MeV energies through closest approach.

We present multi-instrument observations of the effects of solar irradiance on the upper Martian ionosphere and escape fluxes based on the MAVEN data from November 2014 to February 2016. It is shown that fluxes of oxygen ions with E > 30 eV both inside and outside of the Martian magnetosphere are nonsensitive to EUV variations. In contrast, the fluxes of ions with lower energies extracted from the upper ionosphere increase with solar irradiance. Such an enhancement is nonlinear with the EUV variations and exhibits a growth by almost one order of magnitude when the EUV (0.1-50 nm) radiation increases to ≥0.1 W/m2 implying an enhancement of total ion losses of the low-energy component to ∼1.8·1025s−1. The flow of cold ions in the near Mars tail occurs very asymmetrical shifting in the direction opposite to the direction of the the solar wind motional electric field. Fluxes of the low-energy (E ≤ 30 eV) ion component are also nonsensitive to the variations in solar wind dynamic pressure.

The Juno spacecraft was launched on August 5, 2011 and spent nearly 5 years traveling through the inner heliosphere on its way to Jupiter. The Magnetic Field Investigation (MAG) was powered on shortly after launch and obtained vector measurements of the interplanetary magnetic field (IMF) at sample rates from 1 to 64 sample/second. The evolution of the magnetic field with radial distance from the sun is compared to similar observations obtained by Voyagers 1 and 2 and the Ulysses spacecraft, allowing a comparison of the radial evolution between prior solar cycles and the current depressed one. During the current solar cycle, the strength of the IMF has decreased throughout the inner heliosphere. A comparison of the variance of the normal component of the magnetic field shows that near Earth the variability of the IMF is similar during all three solar cycles, but may be less at greater radial distances.

Israeli Ministry of Science; Minerva foundation; Federal German Ministry of Education and Research; Helen Kimmel Center for Planetary Science at the Weizmann Institute of Science; CNES; BSF; NSF; Juno project

Synoptic decametric (DAM) radio observations at Jupiter were made in a broad Jovicentric latitudinal range of −21∘ to +15∘ by the Juno polar orbiting spacecraft from 21 June to 10 December, 2016. We investigated the occurrence probability of non-Io-related DAM. At 19.5 MHz, as Juno's latitude varies from +15∘ to −21∘, a peak of non-Io-B occurrence probability at 175∘ System III central meridian longitude (CML) gradually shifts in longitude to 140∘ CML. Also, another peak occurs at 110∘ CML between −15∘ and −9∘, merging into the bottom edge of the former peak. This J-shaped feature is similarly seen at 16.5 MHz. Using the Jovian magnetic field models, the fixed hollow cone model can reasonably account for the J-shaped structure for radio sources traced along active magnetic flux tubes onto Jupiter's surface projected at about 135∘–149∘ System III longitude. Moreover, these non-Io-B spectral profiles extend from 13.5 to 23.5 MHz.

Juno swoops around giant Jupiter Jupiter is the largest and most massive planet in our solar system. NASA's Juno spacecraft arrived at Jupiter on 4 July 2016 and made its first close pass on 27 August 2016. Bolton et al. present results from Juno's flight just above the cloud tops, including images of weather in the polar regions and measurements of the magnetic and gravitational fields. Juno also used microwaves to peer below the visible surface, spotting gas welling up from the deep interior. Connerney et al. measured Jupiter's aurorae and plasma environment, both as Juno approached the planet and during its first close orbit. Science , this issue p. 821 , p. 826

The Juno spacecraft has crossed Jupiter's bow shock (BS) and magnetopause (MP) multiple times in the dawn sector (near 0600 local time), both during the approach to Jupiter and during the first three apojove periods. A survey of all of these crossings using the Juno field and particle instruments has been performed, with 51 bow shock and 97 magnetopause crossings being detected. The BS crossings ranged from 92 to 128 RJ with 1 encounter during the approach, 36 during the first apojove period, 0 on the second, and 14 during the third. The MP crossings ranged from 73 to 114 RJ, with 8 MP encounters during the approach, 40 encounters during the first apojove period, 24 encounters on the second, and 46 during the third. During the approach, Juno initially encountered an expanding magnetosphere resulting in a single BS and MP crossing, followed a few days later by a contracting magnetosphere, resulting in 7 more MP crossings and a BS crossing on the first outbound orbit at 92 RJ. The lack of BS crossings and the limited number of MP crossings during the second apojove period suggests a long period of an expanded magnetosphere, likely caused by a prolonged period of low solar wind dynamic pressure associated with a rarefaction region. The detection of BS crossings on the third apojove period suggests another period of a highly compressed magnetosphere.

The Juno Waves instrument detected a new broadband plasma wave emission (~50 Hz to 40 kHz) on 27 August 2016 as the spacecraft passed over the low-altitude polar regions of Jupiter. We investigated the characteristics of this emission and found similarities to whistler mode auroral hiss observed at Earth, including a funnel-shaped frequency-time feature. The electron cyclotron frequency is much higher than both the emission frequency and local plasma frequency, which is assumed to be ~20–40 kHz. The E/cB ratio was about three near the start of the event and then decreased to one for the rest of the period. A correlation of the electric field spectral density with the flux of an upgoing 20 to 800 keV electron beam was found, with a correlation coefficient of 0.59. We conclude that the emission is propagating in the whistler mode and is driven by the energetic upgoing electron beam.

Juno obtained unique low-altitude space environment measurements over Jupiter's poles on 27 August 2016. Here Jupiter Energetic-particle Detector Instrument observations are presented for electrons (25–800 keV) and protons (10–1500 keV). We analyze magnetic field-aligned electron angular beams over expected auroral regions that were sometimes symmetric (bidirectional) but more often strongly asymmetric. Included are variable but surprisingly persistent upward, monodirectional electron angular beams emerging from what we term the “polar cap,” poleward of the nominal auroral ovals. The energy spectra of all beams were monotonic and hard (not structured in energy), showing power law-like distributions often extending beyond ~800 keV. Given highly variable downward energy fluxes (below 1 RJ altitudes within the loss cone) as high as 280 mW/m2, we suggest that mechanisms generating these beams are among the primary processes generating Jupiter's uniquely intense auroral emissions, distinct from what is typically observed at Earth.

During the first perijove passage of the Juno mission, the Jovian InfraRed Auroral Mapper (JIRAM) observed a line of closely spaced oval features in Jupiter's southern hemisphere, between 30°S and 45°S. In this work, we focused on the longitudinal region covering the three ovals having higher contrast at 5 μm, i.e., between 120°W and 60°W in System III coordinates. We used the JIRAM's full spectral capability in the range 2.4–3 μm together with a Bayesian data inversion approach to retrieve maps of column densities and altitudes for an NH3 cloud and an N2H4 haze. The deep (under the saturation level) volume mixing ratio and the relative humidity for gaseous ammonia were also retrieved. Our results suggest different vortex activity for the three ovals. Updraft and downdraft together with considerations about the ammonia condensation could explain our maps providing evidences of cyclonic and anticyclonic structures.

After its capture into Jupiter orbit early in the summer of 2016, the Juno spacecraft made three close flybys of the planet to date. The Jupiter Energetic Particle Detector Instrument (JEDI) made continuous measurements during perijoves in late August and early December. Here we describe the radiation (approximately hundreds of keV to more than 10 MeV charged particles) that was measured close to Jupiter. The purpose of this paper is to present some of the first direct energetic charged particle measurements ever obtained at high magnetic latitude very close to Jupiter and to interpret these data using techniques that rely on the instrument design. We generate an electron energy spectrum in an intense radiation region where the JEDI foreground is only about 40% of the rate due to >15 MeV electrons.