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

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

doi:10.1002/2017gl076901

Cited by 60 publications

(130 citation statements)

References 34 publications

(64 reference statements)

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“…In phase space density, this means the spectral slopes at lower energies are often α ≈ 1 to 2, or E −1 to E −2 . The auroral distributions studied by Mauk et al (, ) also show similar spectral shapes at the lower energies. The tail of the distribution at the larger energies, defined as above the peak or rollover in the spectrum, can have spectral slopes that vary dramatically.…”

Section: Discussionmentioning

confidence: 85%

“…For this study, it is important to note that JEDI can measure the energy and angular distributions of ~30 keV to 1 MeV electrons. A single sensor is made up of six solid state detector (SSD) telescopes, each with an instantaneous full width at half maximum FOV of ~9 ° × 17 ° (Mauk et al, ; see their supporting information). The accumulation time during the high rate is ~0.5 s, but we find averaging over 1 second is necessary to avoid poor statistics.…”

Section: Energetic Electron Observationsmentioning

confidence: 99%

“…As mentioned previously, there are several types of energetic electron distributions associated with the main aurora. Previous publications have focused on two general types: broadband with no peak and the peaked distributions (Allegrini et al, ; Clark, Mauk, Paranicas, et al, ; Ebert et al, ; Mauk et al, , , ). Here we expand the list and show the various types of electron distributions (Figure ) associated with the main auroral crossings.…”

Section: Energetic Electron Observationsmentioning

confidence: 99%

“…Juno observations have revealed the presence of diverse electron and ion populations associated with both the upward and downward auroral current regions in Jupiter's polar magnetosphere. Recently published results focusing on the particle observations have shown the presence of both broadband and peaked electron energy distributions in both the downward (Allegrini et al, ; Mauk et al, , , ) and upward (Clark, Mauk, Haggerty, et al, ; Ebert et al, ) loss cones. The auroral ion observations revealed the presence of energetic ion conics (Clark, Mauk, Haggerty, et al, ), parallel potential drops (Clark, Mauk, Haggerty, et al, ; Haggerty et al, ; Mauk et al, , ), and stochastic processes likely associated with wave‐particle interactions (Elliott et al, ; Li et al, ; Louarn et al, Ma et al, ; Mauk et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Precipitating Electron Energy Flux and Characteristic Energies in Jupiter's Main Auroral Region as Measured by Juno/JEDI

et al. 2018

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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.

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Section: Discussionmentioning

confidence: 85%

Section: Energetic Electron Observationsmentioning

confidence: 99%

Section: Energetic Electron Observationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Precipitating Electron Energy Flux and Characteristic Energies in Jupiter's Main Auroral Region as Measured by Juno/JEDI

et al. 2018

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“…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. Contrary to the initial lack of such observations, later spacecraft passes indicated the presence of strong parallel electric fields, coherent particle acceleration, and inverted-V structures Mauk et al, 2018;Paranicas et al, 2018). Juno also observed ion conics on auroral field lines , which may be the result of field-aligned electron beams and the associated broadband whistler waves (Tetrick et al, 2017) similar to the those observed at Earth although at much higher energies.…”

Section: 1029/2019ja027403mentioning

confidence: 79%

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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Gas Giant Magnetosphere–Ionosphere–Thermosphere Coupling

Ray

Yates

2021

Magnetospheres in the Solar System

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Magnetosphere-ionosphere-thermosphere (MIT) coupling describes the exchange of energy and angular momentum between a planet and its surrounding plasma environment.A plethora of phenomena are signatures of this interaction, from bright auroral and radio emissions across multiple wavelengths that are easily observed remotely, to radio bursts and field aligned currents best measured in situ. Gas giant MIT coupling differs from that in the terrestrial system because of rapid planetary rotation rates, dense hydrogenbased atmospheres, and outgassing moons embedded well within the magnetospheres.We discuss here the fundamental physics governing MIT coupling at Jupiter and Saturn. IntroductionMagnetosphere-ionosphere-thermosphere coupling is the process by which energy and angular momentum are transferred between a planet and its surrounding plasma environment. The magnetosphere is host to a variety of plasma populations which are connected to the planetary magnetic field. Stresses associated with changes in magnetic field configuration e.g. magnetic reconnection, magnetospheric compressions or expansions induced by the solar wind, or modifications to the local plasma population e.g. source and/or loss processes such as charge exchange, energisation, plasma injections triggered by reconnection or radial outflow, are communicated to the planet via electrical currents.Electrical currents in the magnetosphere are coupled to the planet through magnetic fieldaligned currents which close in the ionosphere. Ionospheric currents modify the coincident thermosphere by for example, heating the local atmosphere and driving winds. Collisions between ionospheric ions and thermospheric neutrals alter the electric currents and thus can affect magnetospheric plasma. Sections 3 and 4 of this series are dedicated to solar wind-magnetosphere and magnetosphere-ionosphere coupling processes, respectively. We concentrate on MIT coupling at the giant planets here.At Earth, MIT coupling is largely driven by the interaction between the magnetosphere and the solar wind. This is only a fraction of the picture at gas giant planets, where rapid rotation and internal plasma sources combine to drive a more dynamic MIT coupled system. Jupiter and Saturn rotate with periods of ∼9.9 hours and ∼10.7 hours, respectively. Deep within each magnetosphere, moons under tidal stresses release neutral material into the local space environment. Io ejects 700 -3000 kg s −1 neutral material into Jupiter's magnetosphere (Delamere, Bagenal, & Steffl, 2005). At Saturn, Enceladus emits neutrals at a rate of 150 -300 kg s −1 (Hansen et al., 2006). Approximately half of the material remains as plasma in the system following ionization (see Chapter 8.2, this volume). These plasma sources, embedded well within the magnetosphere, modify the MIT coupling throughout the system from that described in Chapter 4.1. Newly generated plasma, which orbited the planet at the Keplerian velocity as neutrals, must be accelerated to corotation with the planetary magnetic field. This accele...

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

Cited by 60 publications

References 34 publications

Precipitating Electron Energy Flux and Characteristic Energies in Jupiter's Main Auroral Region as Measured by Juno/JEDI

Precipitating Electron Energy Flux and Characteristic Energies in Jupiter's Main Auroral Region as Measured by Juno/JEDI

Energetic Particle Signatures Above Saturn's Aurorae

Gas Giant Magnetosphere–Ionosphere–Thermosphere Coupling

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