Search

We present a survey of electron partial densities (i.e., the portion of the total density measured between similar to 0.05 and 100 keV) and temperatures in Jupiter's main auroral emission region using plasma measurements from the Jovian Auroral Distributions Experiment (JADE) on Juno. The electron partial density increases from similar to 0.01 or 0.1 cm(-3) near the main oval to a few cm(-3) at the edge of the measurable part of the UV emission equatorward of the main oval. The electron temperature is highest near the main oval at similar to 10-20 keV and decreases equatorward down to similar to 0.3-2 keV. The JADE electron partial density agrees within a factor of similar to 2 with the total electron densities derived from Juno-Waves when the comparison is possible. The electron density and temperature trends are consistent for all sampled longitudes, for the north and the south, and there is no significant trend with radial distance in the range examined in this study (1.25-1.96 R-J). The electron density is anti-correlated with the temperature and the characteristic energy. The ratio of the magnetic field strength to the electron density is maximum near the main oval.

The Solar System is home to a cloud of dust that orbits the Sun and makes its presence known by virtue of scattered light (Zodiacal Light) that can be seen after dusk and before dawn. Within this cloud are bands of dust orbiting near the ecliptic plane, evidenced by an excess of scattered light at discrete ecliptic latitudes. Dedicated dust detectors borne by spacecraft in transit of the solar system have detected few such particles of the appropriate size owing to limited detector aperture and sparsity of the population. Thus, the distribution, origin, and orbital evolution of the dust in these bands remains a mystery. A star camera aboard the Juno spacecraft traveling from Earth to Jupiter recorded interplanetary dust impacts on the spacecraft in numbers sufficient to characterize the spatial distribution of such particles for the first time. The observed distribution is consistent with a primary source of dust particles sharing the Mars orbit plane between Earth and the 4:1 resonance with Jupiter. We propose that the primary distribution is scattered by orbital resonances with Jupiter via the Kozai-Lidov (KL) effect into a secondary population at higher inclination to the ecliptic. The measured dust distribution, occupying a volume uniquely determined by the orbital elements of Mars and KL scattering, accounts for the observed variation of the Zodiacal Light with ecliptic latitude. Our results provide a compelling alternative to the prevailing theory of the origin and evolution of interplanetary dust observed at low ecliptic latitudes.

The Solar System is home to a cloud of dust that orbits the Sun and makes its presence known by virtue of scattered light (Zodiacal Light) that can be seen after dusk and before dawn. Within this cloud are bands of dust orbiting near the ecliptic plane, evidenced by an excess of scattered light at discrete ecliptic latitudes. Dedicated dust detectors borne by spacecraft in transit of the solar system have detected few such particles of the appropriate size owing to limited detector aperture and sparsity of the population. Thus, the distribution, origin, and orbital evolution of the dust in these bands remains a mystery. A star camera aboard the Juno spacecraft traveling from Earth to Jupiter recorded interplanetary dust impacts on the spacecraft in numbers sufficient to characterize the spatial distribution of such particles for the first time. The observed distribution is consistent with a primary source of dust particles sharing the Mars orbit plane between Earth and the 4:1 resonance with Jupiter. We propose that the primary distribution is scattered by orbital resonances with Jupiter via the Kozai‐Lidov (KL) effect into a secondary population at higher inclination to the ecliptic. The measured dust distribution, occupying a volume uniquely determined by the orbital elements of Mars and KL scattering, accounts for the observed variation of the Zodiacal Light with ecliptic latitude. Our results provide a compelling alternative to the prevailing theory of the origin and evolution of interplanetary dust observed at low ecliptic latitudes.

The Solar System is home to a cloud of dust that orbits the Sun and makes its presence known by virtue of scattered light (Zodiacal Light) that can be seen after dusk and before dawn. Within this cloud are bands of dust orbiting near the ecliptic plane, evidenced by an excess of scattered light at discrete ecliptic latitudes. Dedicated dust detectors borne by spacecraft in transit of the solar system have detected few such particles of the appropriate size owing to limited detector aperture and sparsity of the population. Thus, the distribution, origin, and orbital evolution of the dust in these bands remains a mystery. A star camera aboard the Juno spacecraft traveling from Earth to Jupiter recorded interplanetary dust impacts on the spacecraft in numbers sufficient to characterize the spatial distribution of such particles for the first time. The observed distribution is consistent with a primary source of dust particles sharing the Mars orbit plane between Earth and the 4:1 resonance with Jupiter. We propose that the primary distribution is scattered by orbital resonances with Jupiter via the Kozai-Lidov (KL) effect into a secondary population at higher inclination to the ecliptic. The measured dust distribution, occupying a volume uniquely determined by the orbital elements of Mars and KL scattering, accounts for the observed variation of the Zodiacal Light with ecliptic latitude. Our results provide a compelling alternative to the prevailing theory of the origin and evolution of interplanetary dust observed at low ecliptic latitudes.

Juno was inserted into a polar orbit about Jupiter on July 4th 2016. Juno's magnetic field investigation acquires vector measurements of the Jovian magnetic field using a pair of a tri-axial Fluxgate Magnetometers (FGM) co-located with four attitude-sensing star cameras on an optical bench. The optical bench is placed on a boom at the outer extremity of one of Juno's three solar arrays. The Magnetic Field investigation (MAG) uses measurements of the optical bench inertial attitude provided by the micro Advanced Stellar Compass (μASC) to render accurate vector measurements of the planetary magnetic field. During periJoves, orientation of the MAG Optical Benches (MOB) is determined using the spacecraft (SC) attitude combined with transformations between SC and MOB coordinate frames. Substantial pre-launch effort was expended to maximize the thermo-mechanical stability of the Juno solar arrays and MAG boom. Nevertheless, the Juno flight experience demonstrates that the transformation between SC and MAG reference frames varies significantly in response to spacecraft thermal excursions associated with large attitude maneuvers and proximate encounters with Jupiter. This response is monitored by comparing attitudes provided by the MAG investigation's four Camera Head Units (CHUs) with those provided by the Stellar Reference Unit (SRU). These systematic variations in relative orientation are thought to be caused by the thermo-elastic flexure of the Juno solar array in response to temperature excursions associated with maneuvers and heating during close passages of Jupiter. In this paper, we investigate these thermal effects and propose a model for compensation of the MAG boom flexure.

The Juno spacecraft entered orbit at Jupiter on July 5, 2016. Since then, Juno has orbited Jupiter in high inclination orbits, crossing the ring plane near perijove. During 20 of the first 21 crossings, the Waves instrument detected signals associated with dust impacts. The impact rate profiles show peaks of order 6 s‐1 around the ring plane with half width at half maximum ~2000‐3000 km. The polarity ratio of the impact signals didn't follow the areas of the antennas exposed to dust impacts that change due to the rotation of the spacecraft, suggesting Waves detects impacts on the Juno spacecraft and not just on the Waves antennas. The impact rate profile changed during Perijove 19, when the spacecraft rotation axis was tilted to the south, increasing the area of the solar panels exposed to impacts, indicating that the detected impacts were on the spacecraft body. Grain sizes of order 1 μm are estimated, and the differential size distribution has a slope of ‐5.1 and with number densities of order 3 x 10‐6 m‐3.

The Jovian Auroral Distributions Experiment aboard Juno observed accelerated proton populations connected to Io's footprint tail aurora. While accelerated electron populations have been previously linked with Io's auroral footprint tail aurora, we present new evidence for proton acceleration due to Io's Alfvenic interaction with Jupiter's magnetosphere. Separate populations were accelerated above the Io torus and at high latitudes near Jupiter. The timing suggests the acceleration is due to Alfven waves associated with Io's Main Alfven Wing. The inferred high-latitude proton acceleration region spans 0.9-2.5 Jovian radii in altitude, comparable to the expected location for electron acceleration, and suggests the associated Alfven waves are able to accelerate electrons and protons in similar locations. The proton populations magnetically connected to Io's orbit are recently perturbed, equilibrating with the nominal torus plasma population on a timescale smaller than Io's System III orbital period of similar to 13 h, likely due to wave-particle interactions. The tail populations are split into a wake-like structure with distinct inner and outer regions, where the inner region maps to an equatorial width nearly identical to the diameter of Io. The approximately symmetric surrounding outer regions are each slightly smaller than the central region and may be related to Io's atmospheric extent. The nominal, corotational torus proton population exhibits energization throughout all regions, peaking at the anti-Jovian flank of the inner core region mapping to Io's diameter. These proton observations suggest Alfven waves are capable of accelerating protons in multiple locations and provide further evidence that Io's Alfvenic interaction is bifurcated. Plain Language Summary The interaction between Jupiter's moon Io and Jupiter's rapidly rotating magnetic field produces a persistent aurora in Jupiter's upper atmosphere. The Juno spacecraft's trajectory crossed magnetic field l

Integrating simultaneous in situ measurements of magnetic field fluctuations, precipitating electrons, and ultraviolet auroral emissions, we find that Alfvenic acceleration mechanisms are responsible for Ganymede's auroral footprint tail. Magnetic field perturbations exhibit enhanced Alfvenic activity with Poynting fluxes of similar to 100 mW/m(2). These perturbations are capable of accelerating the observed broadband electrons with precipitating fluxes of similar to 11 mW/m(2), such that Alfvenic power is transferred to electron acceleration with similar to 10% efficiency. The ultraviolet emissions are consistent with in situ electron measurements, indicating 13 +/- 3 mW/m(2) of precipitating electron flux. Juno crosses flux tubes with both upward and downward currents connected to the auroral tail exhibiting small-scale structure. We identify an upward electron conic in the downward current region, possibly due to acceleration by inertial Alfven waves near the Jovian ionosphere. In concert with in situ observations at Io's footprint tail, these results suggest that Alfvenic acceleration processes are broadly applicable to magnetosphere-satellite interactions. Plain Language Summary Jupiter's moon Ganymede interacts with the planet's rapidly rotating magnetic field, which generates an aurora in the Jovian upper atmosphere. The Juno spacecraft crossed magnetic field lines connected to this aurora. We found that a specific type of wave, similar to a wave produced when a string is plucked, is responsible for accelerating the electrons sustaining this aurora. This type of interaction between a moon and the planet it orbits is likely a common process occurring at other exoplanetary systems.

Jupiter's ultraviolet (UV) aurorae, the most powerful and intense in the solar system, are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. Previous studies focused on case analyses and/or greater than 30-keV energy electrons. Here for the first time we provide a comprehensive evaluation of Jovian auroral electron characteristics over the entire relevant range of energies (similar to 100 eV to similar to 1 MeV). The focus is on the first eight perijoves providing a coarse but complete System III view of the northern and southern auroral regions with corresponding UV observations. The latest magnetic field model JRM09 with a current sheet model is used to map Juno's magnetic foot point onto the UV images and relate the electron measurements to the UV features. We find a recurring pattern where the 3- to 30-keV electron energy flux peaks in a region just equatorward of the main emission. The region corresponds to a minimum of the electron characteristic energy (<10 keV). Its polarward edge corresponds to the equatorward edge of the main oval, which is mapped at M shells of similar to 51. A refined current sheet model will likely bring this boundary closer to the expected 20-30 RJ. Outside that region, the >100-keV electrons contribute to most (>similar to 70-80%) of the total downward energy flux and the characteristic energy is usually around 100 keV or higher. We examine the UV brightness per incident energy flux as a function of characteristic energy and compare it to expectations from a model.

We analyze precipitating electron fluxes connected to 18 crossings of Io's footprint tail aurora, over altitudes of 0.15 to 1.1 Jovian radii (R-J). The strength of precipitating electron fluxes is dominantly organized by Io-Alfven tail distance, the angle along Io's orbit between Io and an Alfven wave trajectory connected to the tail aurora. These fluxes best fit an exponential as a function of down-tail extent with ane-folding distance of 21 degrees. The acceleration region altitude likely increases down-tail, and the majority of parallel electron acceleration sustaining the tail aurora occurs above 1R(J)in altitude. We do not find a correlation between the tail fluxes and the power of the initial Alfven wave launched from Io. Finally, Juno has likely transited Io's Main Alfven Wing fluxtube, observing a characteristically distinct signature with precipitating electron fluxes similar to 600 mW/m(2)and an acceleration region extending as low as 0.4R(J)in altitude.

We report the first in situ observations of electron measurements at a Europa footprint tail (FPT) crossing in the auroral region. During its 12th science perijove pass, Juno crossed magnetic field lines connected to Europa's FPT. We find that electrons in the range similar to 0.4 to similar to 25 keV, with a characteristic energy of 3.6 +/- 0.5 keV, precipitate into Jupiter's atmosphere to create the footprint aurora. The energy flux peaks at similar to 36 mW/m(2), while the peak ultraviolet (UV) brightness is estimated at 37 kR. We estimate the peak electron density and temperature to be 17.3 cm(-3) and 1.8 +/- 0.1 keV, respectively. Using magnetic flux shell mapping, we estimate that the radial width of the interaction at Europa's orbit spans roughly 3.6 +/- 1.0 Europa radii. In contrast to typical Io FPT crossings, the instrument background caused by penetrating energetic radiation (> similar to 5-10 MeV electrons) increased during the Europa FPT crossing.

The electrodynamic coupling between Io and Jupiter gives rise to wave-particle interactions across multiple spatial scales. Here we report observations during Juno's 12th perijove (PJ) high-latitude northern crossing of the flux tube connected to Io's auroral footprint. We focus on plasma wave measurements, clearly differentiating between magnetohydrodynamic (MHD), ion, and electron scales. We find (i) evidence of Alfven waves undergoing a turbulent cascade, suggesting Alfvenic acceleration processes together with observations of bi-directional, broadband electrons; (ii) intense ion cyclotron waves with an estimated heating rate that is consistent with the generation of ion conics reported by Clark et al. (2020, ); and (iii) whistler-mode auroral hiss radiation excited by field-aligned electrons. Such high-resolution wave and particle measurements provide an insight into satellite interactions in unprecedented detail. We further anticipate that these spatially well-constrained results can be more broadly applied to better understand processes of Jupiter's main auroral oval.

Observations of energetic charged particles associated with Io's footprint (IFP) tail, and likely within or very near the Main Alfven Wing, during Juno's 12th perijove (PJ) crossing show evidence of intense proton acceleration by wave-particle heating. Measurements made by Juno/JEDI reveal proton characteristics that include pitch angle distributions concentrated along the upward loss cone, broad energy distributions that span similar to 50 keV to 1 MeV, highly structured temporal/spatial variations in the particle intensities, and energy fluxes as high as similar to 100 mW/m(2). Simultaneous measurements of the plasma waves and magnetic field suggest the presence of ion cyclotron waves and transverse Alfvenic fluctuations. We interpret the proton observations as upgoing conics likely accelerated via resonant interactions with ion cyclotron waves. These observations represent the first measurements of ion conics associated with moon-magnetosphere interactions, suggesting energetic ion acceleration plays a more important role in the IFP tail region than previously considered. Plain Language Summary NASA's Juno spacecraft orbits Jupiter's polar region and makes direct measurements of the fields and particles that are responsible for creating Jupiter's powerful auroras. In this article, we present new observations that show intense proton acceleration occurring at altitudes near the auroral emissions created by the interaction between Jupiter's moon Io and the surrounding plasma and magnetic field environment. These unique observations provide clues on how particles are being accelerated and will help constrain particle acceleration theories.

The Jovian Auroral Distributions Experiment aboard Juno observed accelerated proton populations connected to Io's footprint tail aurora. While accelerated electron populations have been previously linked with Io's auroral footprint tail aurora, we present new evidence for proton acceleration due to Io's Alfvenic interaction with Jupiter's magnetosphere. Separate populations were accelerated above the Io torus and at high latitudes near Jupiter. The timing suggests the acceleration is due to Alfven waves associated with Io's Main Alfven Wing. The inferred high-latitude proton acceleration region spans 0.9-2.5 Jovian radii in altitude, comparable to the expected location for electron acceleration, and suggests the associated Alfven waves are able to accelerate electrons and protons in similar locations. The proton populations magnetically connected to Io's orbit are recently perturbed, equilibrating with the nominal torus plasma population on a timescale smaller than Io's System III orbital period of similar to 13 h, likely due to wave-particle interactions. The tail populations are split into a wake-like structure with distinct inner and outer regions, where the inner region maps to an equatorial width nearly identical to the diameter of Io. The approximately symmetric surrounding outer regions are each slightly smaller than the central region and may be related to Io's atmospheric extent. The nominal, corotational torus proton population exhibits energization throughout all regions, peaking at the anti-Jovian flank of the inner core region mapping to Io's diameter. These proton observations suggest Alfven waves are capable of accelerating protons in multiple locations and provide further evidence that Io's Alfvenic interaction is bifurcated. Plain Language Summary The interaction between Jupiter's moon Io and Jupiter's rapidly rotating magnetic field produces a persistent aurora in Jupiter's upper atmosphere. The Juno spacecraft's trajectory crossed magnetic field l

Integrating simultaneous in situ measurements of magnetic field fluctuations, precipitating electrons, and ultraviolet auroral emissions, we find that Alfvenic acceleration mechanisms are responsible for Ganymede's auroral footprint tail. Magnetic field perturbations exhibit enhanced Alfvenic activity with Poynting fluxes of similar to 100 mW/m(2). These perturbations are capable of accelerating the observed broadband electrons with precipitating fluxes of similar to 11 mW/m(2), such that Alfvenic power is transferred to electron acceleration with similar to 10% efficiency. The ultraviolet emissions are consistent with in situ electron measurements, indicating 13 +/- 3 mW/m(2) of precipitating electron flux. Juno crosses flux tubes with both upward and downward currents connected to the auroral tail exhibiting small-scale structure. We identify an upward electron conic in the downward current region, possibly due to acceleration by inertial Alfven waves near the Jovian ionosphere. In concert with in situ observations at Io's footprint tail, these results suggest that Alfvenic acceleration processes are broadly applicable to magnetosphere-satellite interactions. Plain Language Summary Jupiter's moon Ganymede interacts with the planet's rapidly rotating magnetic field, which generates an aurora in the Jovian upper atmosphere. The Juno spacecraft crossed magnetic field lines connected to this aurora. We found that a specific type of wave, similar to a wave produced when a string is plucked, is responsible for accelerating the electrons sustaining this aurora. This type of interaction between a moon and the planet it orbits is likely a common process occurring at other exoplanetary systems.

Jupiter's ultraviolet (UV) aurorae, the most powerful and intense in the solar system, are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. Previous studies focused on case analyses and/or greater than 30-keV energy electrons. Here for the first time we provide a comprehensive evaluation of Jovian auroral electron characteristics over the entire relevant range of energies (similar to 100 eV to similar to 1 MeV). The focus is on the first eight perijoves providing a coarse but complete System III view of the northern and southern auroral regions with corresponding UV observations. The latest magnetic field model JRM09 with a current sheet model is used to map Juno's magnetic foot point onto the UV images and relate the electron measurements to the UV features. We find a recurring pattern where the 3- to 30-keV electron energy flux peaks in a region just equatorward of the main emission. The region corresponds to a minimum of the electron characteristic energy (<10 keV). Its polarward edge corresponds to the equatorward edge of the main oval, which is mapped at M shells of similar to 51. A refined current sheet model will likely bring this boundary closer to the expected 20-30 RJ. Outside that region, the >100-keV electrons contribute to most (>similar to 70-80%) of the total downward energy flux and the characteristic energy is usually around 100 keV or higher. We examine the UV brightness per incident energy flux as a function of characteristic energy and compare it to expectations from a model.

We analyze precipitating electron fluxes connected to 18 crossings of Io's footprint tail aurora, over altitudes of 0.15 to 1.1 Jovian radii (R-J). The strength of precipitating electron fluxes is dominantly organized by Io-Alfven tail distance, the angle along Io's orbit between Io and an Alfven wave trajectory connected to the tail aurora. These fluxes best fit an exponential as a function of down-tail extent with ane-folding distance of 21 degrees. The acceleration region altitude likely increases down-tail, and the majority of parallel electron acceleration sustaining the tail aurora occurs above 1R(J)in altitude. We do not find a correlation between the tail fluxes and the power of the initial Alfven wave launched from Io. Finally, Juno has likely transited Io's Main Alfven Wing fluxtube, observing a characteristically distinct signature with precipitating electron fluxes similar to 600 mW/m(2)and an acceleration region extending as low as 0.4R(J)in altitude.

We report the first in situ observations of electron measurements at a Europa footprint tail (FPT) crossing in the auroral region. During its 12th science perijove pass, Juno crossed magnetic field lines connected to Europa's FPT. We find that electrons in the range similar to 0.4 to similar to 25 keV, with a characteristic energy of 3.6 +/- 0.5 keV, precipitate into Jupiter's atmosphere to create the footprint aurora. The energy flux peaks at similar to 36 mW/m(2), while the peak ultraviolet (UV) brightness is estimated at 37 kR. We estimate the peak electron density and temperature to be 17.3 cm(-3) and 1.8 +/- 0.1 keV, respectively. Using magnetic flux shell mapping, we estimate that the radial width of the interaction at Europa's orbit spans roughly 3.6 +/- 1.0 Europa radii. In contrast to typical Io FPT crossings, the instrument background caused by penetrating energetic radiation (> similar to 5-10 MeV electrons) increased during the Europa FPT crossing.

The electrodynamic coupling between Io and Jupiter gives rise to wave-particle interactions across multiple spatial scales. Here we report observations during Juno's 12th perijove (PJ) high-latitude northern crossing of the flux tube connected to Io's auroral footprint. We focus on plasma wave measurements, clearly differentiating between magnetohydrodynamic (MHD), ion, and electron scales. We find (i) evidence of Alfven waves undergoing a turbulent cascade, suggesting Alfvenic acceleration processes together with observations of bi-directional, broadband electrons; (ii) intense ion cyclotron waves with an estimated heating rate that is consistent with the generation of ion conics reported by Clark et al. (2020, ); and (iii) whistler-mode auroral hiss radiation excited by field-aligned electrons. Such high-resolution wave and particle measurements provide an insight into satellite interactions in unprecedented detail. We further anticipate that these spatially well-constrained results can be more broadly applied to better understand processes of Jupiter's main auroral oval.

Observations of energetic charged particles associated with Io's footprint (IFP) tail, and likely within or very near the Main Alfven Wing, during Juno's 12th perijove (PJ) crossing show evidence of intense proton acceleration by wave-particle heating. Measurements made by Juno/JEDI reveal proton characteristics that include pitch angle distributions concentrated along the upward loss cone, broad energy distributions that span similar to 50 keV to 1 MeV, highly structured temporal/spatial variations in the particle intensities, and energy fluxes as high as similar to 100 mW/m(2). Simultaneous measurements of the plasma waves and magnetic field suggest the presence of ion cyclotron waves and transverse Alfvenic fluctuations. We interpret the proton observations as upgoing conics likely accelerated via resonant interactions with ion cyclotron waves. These observations represent the first measurements of ion conics associated with moon-magnetosphere interactions, suggesting energetic ion acceleration plays a more important role in the IFP tail region than previously considered. Plain Language Summary NASA's Juno spacecraft orbits Jupiter's polar region and makes direct measurements of the fields and particles that are responsible for creating Jupiter's powerful auroras. In this article, we present new observations that show intense proton acceleration occurring at altitudes near the auroral emissions created by the interaction between Jupiter's moon Io and the surrounding plasma and magnetic field environment. These unique observations provide clues on how particles are being accelerated and will help constrain particle acceleration theories.

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 degrees from the Jovigraphic pole and 204.2 degrees 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.

The Juno mission to Jupiter, in polar orbit around the gas giant since 4 July 2016, samples the planet's environment with dedicated particle and fields instruments. Juno's magnetometer investigation employs a pair of boom-mounted vector fluxgate magnetometers colocated with a set of star cameras to map Jupiter's magnetic field with high accuracy. Juno is a spinning spacecraft, rotating at approximately two rotations per minute. In strong magnetic field environments experienced near periapsis, Eddy currents are generated within electrically conductive material near the magnetic sensors. These currents adversely affect measurements of the environment, most evident in the appearance of a spin modulation in the field magnitude. We demonstrate, by finite element modeling and laboratory measurements, that the spin modulation is caused by a physical signal due to Eddy currents generated by the rotation of the conductive spacecraft structure in the presence of a strong magnetic field. We present a finite element model of the induced field and develop a matrix method for removing the Eddy current contribution to the measured field. Juno magnetic field measurements in strong fields are corrected for Eddy current contributions using this model of the interaction.

Observations of energetic charged particles associated with Io’s footprint (IFP) tail, and likely within or very near the Main Alfvén Wing, during Juno’s 12th perijove (PJ) crossing show evidence of intense proton acceleration by wave‐particle heating. Measurements made by Juno/JEDI reveal proton characteristics that include pitch angle distributions concentrated along the upward loss cone, broad energy distributions that span ~50 keV to 1 MeV, highly structured temporal/spatial variations in the particle intensities, and energy fluxes as high as ~100 mW/m2. Simultaneous measurements of the plasma waves and magnetic field suggest the presence of ion cyclotron waves and transverse Alfvénic fluctuations. We interpret the proton observations as upgoing conics likely accelerated via resonant interactions with ion cyclotron waves. These observations represent the first measurements of ion conics associated with moon‐magnetosphere interactions, suggesting energetic ion acceleration plays a more important role in the IFP tail region than previously considered.

The electrodynamic coupling between Io and Jupiter gives rise to wave‐particle interactions across multiple spatial scales. Here we report observations during Juno’s 12th perijove (PJ) high‐latitude northern crossing of the flux tube connected to Io’s auroral footprint. We focus on plasma wave measurements, clearly differentiating between MHD, ion, and electron scales. We find (i) evidence of Alfvén waves undergoing a turbulent cascade, suggesting Alfvénic acceleration processes together with observations of bi‐directional, broadband electrons; (ii) intense ion cyclotron waves with an estimated heating rate that is consistent with the generation of ion conics reported by Clark et al. (in prep); and (iii) whistler‐mode auroral hiss radiation excited by field‐aligned electrons. Such high‐resolution wave and particle measurements provide an insight into satellite interactions in unprecedented detail. We further anticipate that these spatially well‐constrained results can be more broadly applied to better understand processes of Jupiter’s main auroral oval.

NASAs Juno mission entered into polar orbit about Jupiter on July 4th, 2016. Since then 17 science orbits have been completed, systematically mapping the 3D magnetosphere of Jupiter for the first time. Located on the tip one of Juno’s three solar arrays, the Magnetic Field Experiment carries an absolute attitude reference sensor, the fully autonomous “micro Advances Stellar Compass” (μASC) designed and built at the Technical University of Denmark.

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 affect the footprint. Previous observations showed that its atmosphere collapses in eclipse. While remote observers can observe Io's local auroras briefly when Io disappears behind Jupiter, Juno is able to follow the Io footprint in the unlit hemisphere. Theoretical models of the variability of the energy flux fed into the Alfven wings, ultimately powering the footprints, are not sufficiently constrained by observations. For the first time, we use observations of Io's footprint from the Ultraviolet Spectrograph (UVS) on Juno recorded as Io went into eclipse. We benchmark the trend of the footprint brightness using observations by UVS taken over Io's complete orbit and find that the footprint emitted power variation with Jupiter's rotation shows fairly consistent trends with previous observations. Two exploitable data sets provided measurements when Io was simultaneously in eclipse. No statistically significant changes were recorded as Io left and moved into eclipse, respectively, suggesting either that (i) Io's atmospheric densities within and outside eclipse are large enough to produce a saturated plasma interaction, that is, in the saturated state, changes in Io's atmospheric properties to first order do not control the total Alfvenic energy flux, (ii) the atmospheric collapse during the Juno observations was less than previously observed, or (iii) additional processes of the Alfven wings in addition to the Poynting flux generated at Io control the footprint luminosity., QC 20190920

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 affect the footprint. Previous observations showed that its atmosphere collapses in eclipse. While remote observers can observe Io's local auroras briefly when Io disappears behind Jupiter, Juno is able to follow the Io footprint in the unlit hemisphere. Theoretical models of the variability of the energy flux fed into the Alfven wings, ultimately powering the footprints, are not sufficiently constrained by observations. For the first time, we use observations of Io's footprint from the Ultraviolet Spectrograph (UVS) on Juno recorded as Io went into eclipse. We benchmark the trend of the footprint brightness using observations by UVS taken over Io's complete orbit and find that the footprint emitted power variation with Jupiter's rotation shows fairly consistent trends with previous observations. Two exploitable data sets provided measurements when Io was simultaneously in eclipse. No statistically significant changes were recorded as Io left and moved into eclipse, respectively, suggesting either that (i) Io's atmospheric densities within and outside eclipse are large enough to produce a saturated plasma interaction, that is, in the saturated state, changes in Io's atmospheric properties to first order do not control the total Alfvenic energy flux, (ii) the atmospheric collapse during the Juno observations was less than previously observed, or (iii) additional processes of the Alfven wings in addition to the Poynting flux generated at Io control the footprint luminosity.

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 affect the footprint. Previous observations showed that its atmosphere collapses in eclipse. While remote observers can observe Io's local auroras briefly when Io disappears behind Jupiter, Juno is able to follow the Io footprint in the unlit hemisphere. Theoretical models of the variability of the energy flux fed into the Alfven wings, ultimately powering the footprints, are not sufficiently constrained by observations. For the first time, we use observations of Io's footprint from the Ultraviolet Spectrograph (UVS) on Juno recorded as Io went into eclipse. We benchmark the trend of the footprint brightness using observations by UVS taken over Io's complete orbit and find that the footprint emitted power variation with Jupiter's rotation shows fairly consistent trends with previous observations. Two exploitable data sets provided measurements when Io was simultaneously in eclipse. No statistically significant changes were recorded as Io left and moved into eclipse, respectively, suggesting either that (i) Io's atmospheric densities within and outside eclipse are large enough to produce a saturated plasma interaction, that is, in the saturated state, changes in Io's atmospheric properties to first order do not control the total Alfvenic energy flux, (ii) the atmospheric collapse during the Juno observations was less than previously observed, or (iii) additional processes of the Alfven wings in addition to the Poynting flux generated at Io control the footprint luminosity.

A large set of observations of Jupiter's ultraviolet aurora was collected with the Hubble Space Telescope concurrently with the NASA-Juno mission, during an eight-month period, from 30 November 2016 to 18 July 2017. These Hubble observations cover Juno orbits 3 to 7 during which Juno in situ and remote sensing instruments, as well as other observatories, obtained a wealth of unprecedented information on Jupiter's magnetosphere and the connection with its auroral ionosphere. Jupiter's ultraviolet aurora is known to vary rapidly, with timescales ranging from seconds to one Jovian rotation. The main objective of the present study is to provide a simplified description of the global ultraviolet auroral morphology that can be used for comparison with other quantities, such as those obtained with Juno. This represents an entirely new approach from which logical connections between different morphologies may be inferred. For that purpose, we define three auroral subregions in which we evaluate the auroral emitted power as a function of time. In parallel, we define six auroral morphology families that allow us to quantify the variations of the spatial distribution of the auroral emission. These variations are associated with changes in the state of the Jovian magnetosphere, possibly influenced by Io and the Io plasma torus and by the conditions prevailing in the upstream interplanetary medium. This study shows that the auroral morphology evolved differently during the five similar to 2week periods bracketing the times of Juno perijove (PJ03 to PJ07), suggesting that during these periods, the Jovian magnetosphere adopted various states., QC 20180719

A large set of observations of Jupiter's ultraviolet aurora was collected with the Hubble Space Telescope concurrently with the NASA-Juno mission, during an eight-month period, from 30 November 2016 to 18 July 2017. These Hubble observations cover Juno orbits 3 to 7 during which Juno in situ and remote sensing instruments, as well as other observatories, obtained a wealth of unprecedented information on Jupiter's magnetosphere and the connection with its auroral ionosphere. Jupiter's ultraviolet aurora is known to vary rapidly, with timescales ranging from seconds to one Jovian rotation. The main objective of the present study is to provide a simplified description of the global ultraviolet auroral morphology that can be used for comparison with other quantities, such as those obtained with Juno. This represents an entirely new approach from which logical connections between different morphologies may be inferred. For that purpose, we define three auroral subregions in which we evaluate the auroral emitted power as a function of time. In parallel, we define six auroral morphology families that allow us to quantify the variations of the spatial distribution of the auroral emission. These variations are associated with changes in the state of the Jovian magnetosphere, possibly influenced by Io and the Io plasma torus and by the conditions prevailing in the upstream interplanetary medium. This study shows that the auroral morphology evolved differently during the five similar to 2week periods bracketing the times of Juno perijove (PJ03 to PJ07), suggesting that during these periods, the Jovian magnetosphere adopted various states.

Jupiter's aurorae are produced in its upper atmosphere when incoming high-energy electrons precipitate along the planet's magnetic field lines. A northern and a southern main auroral oval are visible, surrounded by small emission features associated with the Galilean moons. We present infrared observations, obtained with the Juno spacecraft, showing that in the case of Io, this emission exhibits a swirling pattern that is similar in appearance to a von Karman vortex street. Well downstream of the main auroral spots, the extended tail is split in two. Both of Ganymede's footprints also appear as a pair of emission features, which may provide a remote measure of Ganymede's magnetosphere. These features suggest that the magnetohydrodynamic interaction between Jupiter and its moon is more complex than previously anticipated.

The relationship between electron energy flux and the characteristic energy of electron distributions in the main auroral loss cone bridges the gap between predictions made by theory and measurements just recently available from Juno. For decades such relationships have been inferred from remote sensing observations of the Jovian aurora, primarily from the Hubble Space Telescope, and also more recently from Hisaki. However, to infer these quantities, remote sensing techniques had to assume properties of the Jovian atmospheric structure-leading to uncertainties in their profile. Juno's arrival and subsequent auroral passes have allowed us to obtain these relationships unambiguously for the first time, when the spacecraft passes through the auroral acceleration region. Using Juno/Jupiter Energetic particle Detector Instrument (JEDI), an energetic particle instrument, we present these relationships for the 30-keV to 1-MeV electron population. Observations presented here show that the electron energy flux in the loss cone is a nonlinear function of the characteristic or mean electron energy and supports both the predictions from Knight (1973, https://doi.org/10.1016/0032-0633(73)90093-7) and magnetohydrodynamic turbulence acceleration theories (e.g., Saur et al., 2003, https://doi.org/10.1029/2002GL015761). Finally, we compare the in situ analyses of Juno with remote Hisaki observations and use them to help constrain Jupiter's atmospheric profile. We find a possible solution that provides the best agreement between these data sets is an atmospheric profile that more efficiently transports the hydrocarbons to higher altitudes. If this is correct, it supports the previously published idea (e.g., Parkinson et al., 2006, https://doi.org/10.1029/2005JE002539) that precipitating electrons increase the hydrocarbon eddy diffusion coefficients in the auroral regions.