Observation and interpretation of energetic ion conics in Jupiter's polar magnetosphere

Clark, G.; Mauk, B. H.; Paranicas, C.; Haggerty, D. K.; Kollmann, P.; Rymer, A. M.; Brown, L. E.; Jaskulek, S.; Schlemm, C. E.; Kim, C.; Peachey, J.; LaVallee, David; Allegrini, F.; Bagenal, F.; Bolton, S. J.; Connerney, J. E. P.; Ebert, R. W.; Hospodarsky, G. B.; Levin, S. M.; Kurth, W. S.; McComas, D. J.; Mitchell, D. G.; Ranquist, D. A.; Valek, P. W.

doi:10.1002/2016gl072325

Cited by 26 publications

(48 citation statements)

References 22 publications

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“…These energies are consistent with findings by Mitchell et al (2009) and similar to those found at Jupiter (e.g., Clark et al, 2017aClark et al, , 2017b but about a hundred times more energetic than at Earth (e.g., Gorney et al, 1985). These energies are consistent with findings by Mitchell et al (2009) and similar to those found at Jupiter (e.g., Clark et al, 2017aClark et al, , 2017b but about a hundred times more energetic than at Earth (e.g., Gorney et al, 1985).…”

Section: Conclusion and Summarysupporting

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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Section: Conclusion and Summarysupporting

confidence: 89%

Energetic Particle Signatures Above Saturn's Aurorae

et al. 2020

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“…The previous work discussed earlier focused on ions with incident energies between 1 and 2 MeV/u, as these high ion energies are responsible for X‐ray emissions. However, we now know that ions with a wide range of energies precipitate into the polar cap, as confirmed by National Aeronautics and Space Administration (NASA)'s Juno spacecraft (Clark, Mauk, Haggerty, et al, ; Clark, Mauk, Paranicas, et al, ; Connerney et al, ; Haggerty et al, ; Szalay et al, ). Hence, we now model a much broader range of incident ion energies than previously considered (i.e., from 10 keV/u to 5 MeV/u).…”

Section: Physical Processes and Model Descriptionmentioning

confidence: 95%

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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“…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%

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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Observation and interpretation of energetic ion conics in Jupiter's polar magnetosphere

Cited by 26 publications

References 22 publications

Energetic Particle Signatures Above Saturn's Aurorae

Energetic Particle Signatures Above Saturn's Aurorae

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

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

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