Radiation near Jupiter detected by Juno/JEDI during PJ1 and PJ3

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Energetic charged particle measurements by the Jupiter Energetic Particle Detector Instrument (JEDI) on board Juno have revealed a radiation belt of hundreds of keV ions up to the atomic mass of sulfur, located between Jupiter's rings and atmosphere. Proton energy spectra display an unusual intensity increase above 300 keV. We suggest that this is because charge exchange in Jupiter's neutral environment does not efficiently remove ions at such high energies. Since this innermost belt includes heavy ions, it cannot be exclusively supplied by cosmic ray albedo neutron decay, which is an important source at Earth and Saturn but only supplies protons and electrons. We find indications that the stripping of energetic neutral atoms in Jupiter's high atmosphere might be the ion source. Since the stripped off electrons are of low energy, this hypothesis is consistent with observations of the ratio of energetic electrons to ions being much less than 1.

Section: Regions Of the Magnetospherementioning

confidence: 59%

Section: Regions Of the Magnetospherementioning

confidence: 99%

A heavy ion and proton radiation belt inside of Jupiter's rings

Kollmann

Paranicas

Clark

et al. 2017

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“…It corresponds to the fraction of higher energy electrons, beginning at about 400 keV, that fully penetrate the 0.5 mm solid state detectors and leave behind a “minimum ionizing” feature. These are primarily foreground electrons (having reached the detector through the collimator) and are not (mostly) the >15 MeV electrons that reach the detector through the instrument housing (Paranicas et al, ). We have developed procedures for correcting for the penetrator features for individual spectra (supporting information S1).…”

Section: New Observationsmentioning

confidence: 99%

Diverse Electron and Ion Acceleration Characteristics Observed Over Jupiter's Main Aurora

Mauk

Haggerty

Paranicas

et al. 2018

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119

Two new Juno‐observed particle features of Jupiter's main aurora demonstrate substantial diversity of processes generating Jupiter's mysterious auroral emissions. It was previously speculated that sometimes‐observed potential‐driven aurora (up to 400 kV) can turn into broadband stochastic acceleration (dominating at Jupiter) by means of instability. Here direct evidence for such a process is revealed with a “mono‐energetic” electron inverted‐V rising in energy to 200 keV, transforming into a region of broadband acceleration with downward energy fluxes tripling to 3,000 mW/m2, and then transforming back into a mono‐energetic structure ramping down from 200 keV. But a second feature of interest observed nearby is unlikely to have operated in the same way. Here a downward accelerated proton inverted‐V, with inferred potentials to 300–400 kV, occurred simultaneously with downward accelerated broadband electrons with downward energy fluxes as high as any observed (~3,000 mW/m2). This latter feature has no known precedent with Earth auroral observations.

“…Boundary (a) maps to M shell values of 5.7 R J (north) and 6.5 R J (south), with boundary (b) mapping to 8.4 R J (north) and 10.5 R J (south). When connected to M shells inside of (a), JADE experienced large fluxes of penetrating radiation due to the radiation belts [ Paranicas et al ., ] with little indication of a low‐energy plasma population within the JADE energy ranges above noise levels. Between (a) and (b), JADE measured heavy ion populations dominated by M / q = 16, corresponding to O + and/or S ++ that spanned an energy range of a few hundred eV to tens of keV, up to the top of the JADE‐I measurement range (Figure ).…”

Section: High‐latitude Observationsmentioning

confidence: 99%

Plasma measurements in the Jovian polar region with Juno/JADE

Szalay

Allegrini

Bagenal

et al. 2017

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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 on board 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.