Juno observations of energetic charged particles over Jupiter's polar regions: Analysis of monodirectional and bidirectional electron beams

Mauk, B. H.; Haggerty, D. K.; Paranicas, C.; Clark, G.; Kollmann, P.; Rymer, A. M.; Mitchell, D. G.; Bolton, S. J.; Levin, S. M.; Adriani, A.; Allegrini, F.; Bagenal, F.; Connerney, J. E. P.; Gladstone, G. R.; Kurth, W. S.; McComas, D. J.; Ranquist, D. A.; Szalay, J. R.; Valek, P. W.

doi:10.1002/2016gl072286

Cited by 107 publications

(209 citation statements)

References 32 publications

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“…These PADs of Saturn's energetic electrons also resemble the unidirectional and bidirectional distributions recently detected at similar energies by the JEDI instrument on the Juno spacecraft at Jupiter (Mauk et al, 2017b(Mauk et al, , 2017a. In some instances, the Jovian spectra exhibit a peak and/or cutoff in their energy spectra that indicate a field-aligned potential.…”

Section: /2018gl077656supporting

confidence: 73%

Energetic Electron Pitch Angle Distributions During the Cassini Final Orbits

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Mitchell

Kollmann

et al. 2018

Geophysical Research Letters

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Pitch angle distributions (PADs) of very energetic electrons (110–365 keV) are examined during the ring‐grazing and proximal orbits of the Cassini spacecraft, from day 320 2016 (15 November) to day 257 2017 (14 September). These repeating orbits allowed a statistical evaluation of the PADs within the magnetopause on the nightside of Saturn. Along L‐shells (i.e., equatorial crossing distances of magnetic field lines) near and outside that of Titan and north of the equator, the electron fluxes were unidirectionally field‐aligned going away from Saturn. Along L‐shells inside Titan's and south of the equator, the electrons had bidirectional or pancake (trapping) PADs. This behavior suggests that the field lines within Titan's L‐shell are generally closed, while those outside of that L‐shell are generally open. This result strictly applies only to the nightside local times sampled during the final Cassini orbits, but one may infer a similar behavior at other times.

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Section: /2018gl077656supporting

confidence: 73%

Energetic Electron Pitch Angle Distributions During the Cassini Final Orbits

Carbary

Mitchell

Kollmann

et al. 2018

Geophysical Research Letters

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“…They indicate upward (out of the planet) electron beams that reach relativistic energies beyond the scope of the instrument, unlike the lower energies predicted by ion precipitation, which also cannot be seen by JADE. Mauk et al () use the JEDI instrument to analyze higher energy electron beams (25–800 keV) for the same Perijove pass, showing electron counts up to the energy limit of the instrument.…”

Section: Resultsmentioning

confidence: 99%

“…This includes the current density from both the penetrating oxygen ions and the resultant secondary electrons escaping from the top of the atmosphere (Table ), creating additional currents. Mauk et al () estimate a downward current density between 0.11 and 0.13 μA/m 2 for a northern polar cap pass. As more Juno data is gathered, comparing the measured ion fluxes with the field‐aligned current will help to further constrain our model and understand the MI coupling processes taking place at Jupiter.…”

Section: Resultsmentioning

confidence: 99%

Jovian Auroral Ion Precipitation: Field‐Aligned Currents and Ultraviolet Emissions

et al. 2018

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A model is described for the transport of magnetospheric oxygen ions with low charge state and energies up to several MeV/nucleon (MeV/u) as they precipitate into Jupiter's polar atmosphere. A revised and updated hybrid Monte Carlo model originally developed by Ozak et al. (2010, https://doi.org/10.1029/2010JA015635) is used to model the Jovian X‐ray aurora. The current model uses a wide range of incident oxygen ion energies (10 keV/u to 5 MeV/u) and the most up‐to‐date collision cross sections. In addition, the effects of the secondary electrons generated from the heavy ion precipitation are included using a two‐stream transport model that computes the secondary electron fluxes and their escape from the atmosphere. The model also determines H2 Lyman‐Werner band emission intensities, including a predicted spectrum and the associated color ratio. Implications of the new model results for interpretation of data from National Aeronautics and Space Administration's Juno mission are discussed. In particular, the model predicts that for a 2 MeV/u oxygen ion energy input of 10 mW/m2: (1) escaping electrons are produced with an energy range from 1 eV to 4 keV, which is a smaller range than previous models by Ozak et al. (2013, https://doi.org/10.1002/2013GL50812) predicted, (2) H2 band emission rates of 75 kR are generated, similar to previous estimates, and (3) a newly calculated Lyman and Werner band color ratio of 10 is expected. The color ratios are put into a context of various methane number density distributions.

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“…The accelerated ion beam and conic fluxes were shown to vary with solar illumination (Peterson et al, 2006). However, the first passes through Jupiter's auroral region did not reveal a powerful acceleration region and strong field-aligned currents (FACs) as expected (Cowley et al, 2017;Ray et al, 2010; but weaker FACs of a filamentary nature and signatures of aurorae powered by stochastic/broadband acceleration processes substantially different from those at Earth Mauk et al, 2017bMauk et al, , 2017a. Prior to the arrival of NASA's Juno spacecraft at Jupiter, the wave-particle interaction processes responsible for auroral acceleration at the giant planets were nevertheless assumed to be similar to what is observed in the terrestrial magnetosphere.…”

Section: /2019ja027403mentioning

confidence: 89%

Energetic Particle Signatures Above Saturn's Aurorae

et al. 2020

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Near the end of its mission, NASA's Cassini spacecraft performed several low-altitude passes across Saturn's auroral region. We present ultraviolet auroral imagery and various coincident particle and field measurements of two such passes, providing important information about the structure and dynamics of Saturn's auroral acceleration region. In upward field-aligned current regions, upward proton beams are observed to reach energies of several tens of keV; the associated precipitating electron populations are found to have mean energies of about 10 keV. With no significant wave activity being apparent, these findings indicate strong parallel potentials responsible for auroral acceleration, about 100 times stronger than at Earth. This is further supported by observations of proton conics in downward field-aligned current regions above the acceleration region, which feature a lower energy cutoff above ∼50 keV-indicating energetic proton populations trapped by strong parallel potentials while being transversely energized until they can overcome the trapping potential, likely through wave-particle interactions. A spacecraft pass through a downward current region at an altitude near the acceleration region reveals plasma wave features, which may be driving the transverse proton acceleration generating the conics. Overall, the signatures observed resemble those related to the terrestrial and Jovian aurorae, the particle energies and potentials at Saturn appearing to be significantly higher than at Earth and comparable to those at Jupiter.Plain Language Summary NASA's Cassini spacecraft orbited closer to Saturn than ever before during the last stage of its mission, the "Grand Finale". This allowed the onboard instruments to measure charged particles and plasma waves directly above the auroral region while simultaneously providing high-resolution imagery of the ultraviolet aurorae. Based on observations of highly energetic ions streaming away from the planet in regions of low plasma wave activity, we infer the existence of strong electric fields which act to accelerate electrons down into the atmosphere, driving the bright auroral emissions. Our estimates of the average energy of the precipitating electrons support this finding. Charged ions sometimes seem to be energized by plasma waves above the aurorae before they can escape, but the exact process in which this happens is not fully understood. Most signatures presented here resemble those observed in relation to Earth's aurorae, suggesting that the mechanisms acting at both planets are quite similar although Saturn's acceleration mechanism is significantly stronger.

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Juno observations of energetic charged particles over Jupiter's polar regions: Analysis of monodirectional and bidirectional electron beams

Cited by 107 publications

References 32 publications

Energetic Electron Pitch Angle Distributions During the Cassini Final Orbits

Energetic Electron Pitch Angle Distributions During the Cassini Final Orbits

Jovian Auroral Ion Precipitation: Field‐Aligned Currents and Ultraviolet Emissions

Energetic Particle Signatures Above Saturn's Aurorae

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