At Jupiter, part of the auroral radio emissions are induced by the Galilean moons Io, Europa and Ganymede. Until now, except for Ganymede, they have been only remotely detected, using ground-based radio-telescopes or electric antennas aboard spacecraft. The polar trajectory of the Juno orbiter allows the spacecraft to cross the range of magnetic flux tubes which sustain the various Jupiter-satellite interactions, and in turn to sample in situ the associated radio emission regions. In this study, we focus on the detection and the characterization of radio sources associated with Io, Europa and Ganymede. Using electric wave measurements or radio observations (Juno/Waves), in situ electron measurements (Juno/JADE-E), and magnetic field measurements (Juno/MAG) we demonstrate that the Cyclotron Maser Instability (CMI) driven by a loss-cone electron distribution function is responsible for the encountered radio sources. We confirmed that radio emissions are associated with Main (MAW) or Reflected Alfvén Wing (RAW), but also show that for Europa and Ganymede, induced radio emissions are associated with Transhemispheric Electron Beam (TEB). For each traversed radio source, we determine the latitudinal extension, the CMI-resonant electron energy, and the bandwidth of the emission. We show that the presence of Alfvén perturbations and downward field aligned currents are necessary for the radio emissions to be amplified.

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We present multi-instrument Juno observations on day-of-year 86, 2017 that link particles and fields in Jupiter’s polar magnetosphere to transient UV emissions in Jupiter’s northern auroral region known as dawn storms. Juno ranged from 42ºN - 51ºN in magnetic latitude and 5.8 – 7.8 jovian radii (1 RJ = 71,492 km) during this period. These dawn storm emissions consisted of two separate, elongated structures which extended into the nightside, rotated with the planet, had enhanced brightness (up to at least 1.4 megaRayleigh) and high color ratios. The color ratio is a proxy for the atmospheric penetration depth and therefore the energy of the electrons that produce the UV emissions. Juno observed electrons and ions on magnetic field lines mapping to these emissions. The electrons were primarily field-aligned, bi-directional, and, at times, exhibited sudden intensity decreases below ~10 keV coincident with intensity enhancements up to energies of ~1000 keV, consistent with the high color ratio observations. The more energetic electron distributions had characteristic energies of ~160 – 280 keV and downward energy fluxes (~70 – 135 mW/m2) that were a significant fraction needed to produce the UV emissions for this event. Magnetic field perturbations up to ~0.7% of the local magnetic field showing evidence of upward and downward field-aligned currents, whistler mode waves, and broadband kilometric radio emissions were also observed along Juno’s trajectory during this timeframe. These high latitude observations show similarities to those in the equatorial magnetosphere associated with dynamics processes such as interchange events, plasma injections, and/or tail reconnection.

At Jupiter, part of the auroral radio emissions are induced by the Galilean moons Io, Europa and Ganymede. Until now, they have been remotely detected, using ground-based radio-telescopes or electric antennas aboard spacecraft. The polar trajectory of the Juno orbiter allows the spacecraft to cross the magnetic flux tubes connected to these moons, or their tail, and gives a direct measure of the characteristics of these decametric moon–induced radio emissions. In this study, we focus on the detection of a radio emission during the crossing of the Ganymede flux tube. Using electromagnetic waves (Juno/Waves) and in-situ electron measurements (Juno/JADE-E), we estimate the flux tube width to be a few 100 km, a growth rate of the radio emission >3x10-4, an electron population of energy E=4-15 keV and an emission beaming angle of θ=76°-83°, at a frequency 1.005-1.021xfce. We also confirmed that radio emission is associated with Ganymede’s down-tail far-ultraviolet emission.

Solar Orbiter is an ESA/NASA mission that will provide an unprecedented opportunity to discover the fundamental connections between the rapidly varying solar atmosphere and the solar wind. The Solar Wind Analyzer (SWA) plasma package shall provide comprehensive in situ measurements of the solar wind. In particular, the Proton-Alpha Sensor (PAS) will determine the high time resolution properties solar wind ion populations through the measurement of the 3D distribution function, density, bulk velocity, temperature and heat Vux. The closest approach of Solar Orbiter to the Sun is 0.28 AU. At this distance the solar wind Vow, solar UV, and solar infrared Vuxes increase by a factor 13 compared to near-Earth space. The PAS instrument will provide high cadence 3D distribution function measurements (up to 13 per second) all the way from closest approach to 1 AU. The extreme UV and thermal conditions at closest approach precluded the use of standard ion optics schemes. We thus developed a new ion sensor optic design combined with conventional robust channeltron detectors. This paper describes the PAS measurement scheme adopted for varying solar wind conditions and our approach to the fast sampling of 3D distribution functions. We also highlight the expected scienti:c return of the instrument.

Solar wind electrons play an important role in the energy balance of the solar wind acceleration by carrying energy into interplanetary space in the form of electron heat flux. The heat flux is stored in the complex electron velocity distribution functions (VDFs) shaped by expansion, Coulomb collisions, and field-particle interactions. We investigate how the suprathermal electron deficit in the anti-strahl direction, which was recently discovered in the near-Sun solar wind, drives a kinetic instability and creates whistler waves with wave vectors that are quasi-parallel to the direction of the background magnetic field. We combined high-cadence measurements of electron pitch-angle distribution functions and electromagnetic waves provided by Solar Orbiter during its first orbit. Our case study is based on a burst-mode data interval from the Electrostatic Analyser System (SWA-EAS) at a distance of 112 RS (0.52 au) from the Sun, during which several whistler wave packets were detected by Solar Orbiter’s Radio and Plasma Waves (RPW) instrument. The sunward deficit creates kinetic conditions under which the quasi-parallel whistler wave becomes unstable. We directly test our predictions for the existence of these waves through solar wind observations. We find whistler waves that are quasi-parallel and almost circularly polarised, propagating away from the Sun, coinciding with a pronounced sunward deficit in the electron VDF. The cyclotron-resonance condition is fulfilled for electrons moving in the direction opposite to the direction of wave propagation, with energies corresponding to those associated with the sunward deficit. The quasilinear diffusion of the resonant electrons tends to fill the deficit, leading to a reduction in the total electron heat flux.