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Kollmann P, Roussos E, Paranicas C, Woodfield EE, Mauk BH, Clark G, Smith DC, Vandegriff J. Electron Acceleration to MeV Energies at Jupiter and Saturn. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2018; 123:9110-9129. [PMID: 30775196 PMCID: PMC6360449 DOI: 10.1029/2018ja025665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Revised: 08/16/2018] [Accepted: 09/24/2018] [Indexed: 06/09/2023]
Abstract
The radiation belts and magnetospheres of Jupiter and Saturn show significant intensities of relativistic electrons with energies up to tens of megaelectronvolts (MeV). To date, the question on how the electrons reach such high energies is not fully answered. This is largely due to the lack of high-quality electron spectra in the MeV energy range that models could be fit to. We reprocess data throughout the Galileo orbiter mission in order to derive Jupiter's electron spectra up to tens of MeV. In the case of Saturn, the spectra from the Cassini orbiter are readily available and we provide a systematic analysis aiming to study their acceleration mechanisms. Our analysis focuses on the magnetospheres of these planets, at distances of L > 20 and L > 4 for Jupiter and Saturn, respectively, where electron intensities are not yet at radiation belt levels. We find no support that MeV electrons are dominantly accelerated by wave-particle interactions in the magnetospheres of both planets at these distances. Instead, electron acceleration is consistent with adiabatic transport. While this is a common assumption, confirmation of this fact is important since many studies on sources, losses, and transport of energetic particles rely on it. Adiabatic heating can be driven through various radial transport mechanisms, for example, injections driven by the interchange instability or radial diffusion. We cannot distinguish these processes at Saturn with our technique. For Jupiter, we suggest that the dominating acceleration process is radial diffusion because injections are never observed at MeV energies.
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Affiliation(s)
- P. Kollmann
- The Johns Hopkins University, Applied Physics LaboratoryLaurelMDUSA
| | - E. Roussos
- Max Planck Institute for Solar System ResearchGóttingenGermany
| | - C. Paranicas
- The Johns Hopkins University, Applied Physics LaboratoryLaurelMDUSA
| | | | - B. H. Mauk
- The Johns Hopkins University, Applied Physics LaboratoryLaurelMDUSA
| | - G. Clark
- The Johns Hopkins University, Applied Physics LaboratoryLaurelMDUSA
| | - D. C. Smith
- The Johns Hopkins University, Applied Physics LaboratoryLaurelMDUSA
| | - J. Vandegriff
- The Johns Hopkins University, Applied Physics LaboratoryLaurelMDUSA
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Krimigis SM, Carbary JF, Keath EP, Armstrong TP, Lanzerotti LJ, Gloeckler G. General characteristics of hot plasma and energetic particles in the Saturnian magnetosphere: Results from the Voyager spacecraft. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja088ia11p08871] [Citation(s) in RCA: 268] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Acuña MH, Connerney JEP, Ness NF. TheZ3zonal harmonic model of Saturn's magnetic field: Analyses and implications. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja088ia11p08771] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Chenette DL, Stone EC. The Mimas Ghost revisited: An analysis of the electron flux and electron microsignatures observed in the vicinity of Mimas at Saturn. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja088ia11p08755] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Armstrong TP, Paonessa MT, Bell EV, Krimigis SM. Voyager observations of Saturnian ion and electron phase space densities. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja088ia11p08893] [Citation(s) in RCA: 213] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Carbary JF, Krimigis SM, Ip WH. Energetic particle microsignatures of Saturn's satellites. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja088ia11p08947] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Kollmann P, Roussos E, Paranicas C, Krupp N, Jackman CM, Kirsch E, Glassmeier KH. Energetic particle phase space densities at Saturn: Cassini observations and interpretations. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010ja016221] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- P. Kollmann
- Max Planck Institute for Solar System Research; Katlenburg-Lindau Germany
- Institut für Geophysik und Extraterrestrische Physik; Technische Universität Braunschweig; Braunschweig Germany
| | - E. Roussos
- Max Planck Institute for Solar System Research; Katlenburg-Lindau Germany
| | - C. Paranicas
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
| | - N. Krupp
- Max Planck Institute for Solar System Research; Katlenburg-Lindau Germany
| | - C. M. Jackman
- Department of Physics and Astronomy; University College London; London UK
| | - E. Kirsch
- Max Planck Institute for Solar System Research; Katlenburg-Lindau Germany
| | - K.-H. Glassmeier
- Max Planck Institute for Solar System Research; Katlenburg-Lindau Germany
- Institut für Geophysik und Extraterrestrische Physik; Technische Universität Braunschweig; Braunschweig Germany
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Roussos E, Jones GH, Krupp N, Paranicas C, Mitchell DG, Lagg A, Woch J, Motschmann U, Krimigis SM, Dougherty MK. Electron microdiffusion in the Saturnian radiation belts: Cassini MIMI/LEMMS observations of energetic electron absorption by the icy moons. ACTA ACUST UNITED AC 2007. [DOI: 10.1029/2006ja012027] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- E. Roussos
- Max-Planck-Institut für Sonnensystemforschung; Katlenburg-Lindau Germany
| | - G. H. Jones
- Max-Planck-Institut für Sonnensystemforschung; Katlenburg-Lindau Germany
| | - N. Krupp
- Max-Planck-Institut für Sonnensystemforschung; Katlenburg-Lindau Germany
| | - C. Paranicas
- John Hopkins University; Applied Physics Laboratory; Laurel Maryland USA
| | - D. G. Mitchell
- John Hopkins University; Applied Physics Laboratory; Laurel Maryland USA
| | - A. Lagg
- Max-Planck-Institut für Sonnensystemforschung; Katlenburg-Lindau Germany
| | - J. Woch
- Max-Planck-Institut für Sonnensystemforschung; Katlenburg-Lindau Germany
| | - U. Motschmann
- Institut für Theoretische Physik; TU Braunschweig; Braunschweig Germany
| | - S. M. Krimigis
- John Hopkins University; Applied Physics Laboratory; Laurel Maryland USA
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Jones GH, Roussos E, Krupp N, Paranicas C, Woch J, Lagg A, Mitchell DG, Krimigis SM, Dougherty MK. Enceladus' Varying Imprint on the Magnetosphere of Saturn. Science 2006; 311:1412-5. [PMID: 16527968 DOI: 10.1126/science.1121011] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The bombardment of Saturn's moon Enceladus by >20-kiloelectron volt magnetospheric particles causes particle flux depletions in regions magnetically connected to its orbit. Irrespective of magnetospheric activity, proton depletions are persistent, whereas electron depletions are quickly erased by magnetospheric processes. Observations of these signatures by Cassini's Magnetospheric Imaging Instrument allow remote monitoring of Enceladus' gas and dust environments. This reveals substantial outgassing variability at the moon and suggests increased dust concentrations at its Lagrange points. The characteristics of the particle depletions additionally provide key radial diffusion coefficients for energetic electrons and an independent measure of the inner magnetosphere's rotation velocity.
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Affiliation(s)
- G H Jones
- Max Planck Institut für Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany.
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Randall BA. An improved magnetic field model for Jupiter's inner magnetosphere using a microsignature of Amalthea. ACTA ACUST UNITED AC 1998. [DOI: 10.1029/98ja01437] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Stone EC, Cummings AC, Loooper MD, Selesnick RS, Lal N, McDonald FB, Trainor JH, Chenette DL. Energetic Charged Particles in the Magnetosphere of Neptune. Science 1989; 246:1489-94. [PMID: 17756005 DOI: 10.1126/science.246.4936.1489] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The Voyager 2 cosmic ray system (CRS) measured significant fluxes of energetic [>/=1 megaelectron volt (MeV)] trapped electrons and protons in the magnetosphere of Neptune. The intensities are maximum near a magnetic L shell of 7, decreasing closer to the planet because of absorption by satellites and rings. In the region of the inner satellites of Neptune, the radiation belts have a complicated structure, which provides some constraints on the magnetic field geometry of the inner magnetosphere. Electron phase-space densities have a positive radial gradient, indicating that they diffuse inward from a source in the outer magnetosphere. Electron spectra from 1 to 5 MeV are generally well represented by power laws with indices near 6, which harden in the region of peak flux to power law indices of 4 to 5. Protons have significantly lower fluxes than electrons throughout the magnetosphere, with large anisotropies due to radial intensity gradients. The radiation belts resemble those of Uranus to the extent allowed by the different locations of the satellites, which limit the flux at each planet.
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Stone EC, Cooper JF, Cummings AC, McDonald FB, Trainor JH, Lal N, McGuire R, Chenette DL. Energetic Charged Particles in the Uranian Magnetosphere. Science 1986; 233:93-7. [PMID: 17812896 DOI: 10.1126/science.233.4759.93] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
During the encounter with Uranus, the cosmic ray system on Voyager 2 measured significant fluxes of energetic electrons and protons in the regions of the planets magnetosphere where these particles could be stably trapped. The radial distribution of electrons with energies of megaelectron volts is strongly modulated by the sweeping effects ofthe three major inner satellites Miranda, Ariel, and Umbriel. The phase space density gradient of these electrons indicates that they are diffusing radially inward from a source in the outer magnetosphere or magnetotail. Differences in the energy spectra of protons having energies of approximately 1 to 8 megaelectron volts from two different directions indicate a strong dependence on pitch angle. From the locations of the absorption signatures observed in the electron flux, a centered dipole model for the magnetic field of Uranus with a tilt of 60.1 degrees has been derived, and a rotation period of the planet of 17.4 hours has also been calculated. This model provides independent confirmaton of more precise determinations made by other Voyager experiments.
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Paonessa M, Cheng AF. Limits on ion radial diffusion coefficients in Saturn's inner magnetosphere. ACTA ACUST UNITED AC 1986. [DOI: 10.1029/ja091ia02p01391] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Hood LL. Radial diffusion of low-energy ions in Saturn's radiation belts: A Combined analysis of phase space density and satellite microsignature data. ACTA ACUST UNITED AC 1985. [DOI: 10.1029/ja090ia07p06295] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Blake JB, Hilton HH, Margolis SH. On the injection of cosmic ray secondaries into the inner Saturnian magnetosphere: 1. Protons from the CRAND Process. ACTA ACUST UNITED AC 1983. [DOI: 10.1029/ja088ia02p00803] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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McKibben RB, Pyle KR, Simpson JA. Pioneer 11 observations of trapped particle absorption by Amalthea. ACTA ACUST UNITED AC 1983. [DOI: 10.1029/ja088ia01p00036] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Abstract
An overview of the Voyager 2 encounter with Saturn is presented, including a brief discussion of the trajectory, the planned observations, and highlights of the results described in the subsequent reports.
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Vogt RE, Chenette DL, Cummings AC, Garrard TL, Stone EC, Schardt AW, Trainor JH, Lal N, McDonald FB. Energetic Charged Particles in Saturn's Magnetosphere: Voyager 2 Results. Science 1982; 215:577-82. [PMID: 17771281 DOI: 10.1126/science.215.4532.577] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Results from the cosmic-ray system on Voyager 2 in Saturn's magnetosphere are presented. During the inbound pass through the outer magnetosphere, the >/= 0.43-million-electron-volt proton flux was more intense, and both the proton and electron fluxes were more variable, than previously observed. These changes are attributed to the influence on the magnetosphere of variations in the solar wind conditions. Outbound, beyond 18 Saturn radii, impulsive bursts of 0.14- to > 1.0- million-electron-volt electrons were observed. In the inner magnetosphere, the charged particle absorption signatures of Mimas, Enceladus, and Tethys are used to constrain the possible tilt and offset of Saturn's internal magnetic dipole. At approximately 3 Saturn radii, a transient decrease was observed in the electron flux which was not due to Mimas. Characteristics of this decrease suggest the existence of additional material, perhaps another satellite, in the orbit of Mimas.
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Krimigis SM, Armstrong TP, Axford WI, Bostrom CO, Gloeckler G, Keath EP, Lanzerotti LJ, Carbary JF, Hamilton DC, Roelof EC. Low-Energy Charged Particles in Saturn's Magnetosphere: Results from Voyager 1. Science 1981; 212:225-31. [PMID: 17783834 DOI: 10.1126/science.212.4491.225] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The low-energy charged particle instrument on Voyager 1 measured low-energy electrons and ions (energies >/= 26 and >/= 40 kiloelectron volts, respectively) in Saturn's magnetosphere. The first-order ion anisotropies on the dayside are generally in the corotation direction with the amplitude decreasing with decreasing distance to the planet. The ion pitch-angle distributions generally peak at 90 degrees , whereas the electron distributions tend to have field-aligned bidirectional maxima outside the L shell of Rhea. A large decrease in particle fluxes is seen near the L shell of Titan, while selective particle absorption (least affecting the lowest energy ions) is observed at the L shells of Rhea, Dione, and Tethys. The phase space density of ions with values of the first invariant in the range approximately 300 to 1000 million electron volts per gauss is consistent with a source in the outer magnetosphere. The ion population at higher energies (>/= 200 kiloelectron volts per nucleon) consists primarily of protons, molecular hydrogen, and helium. Spectra of all ion species exhibit an energy cutoff at energies >/= 2 million electron volts. The proton-to-helium ratio at equal energy per nucleon is larger (up to approximately 5 x 10(3)) than seen in other magnetospheres and is consistent with a local (nonsolar wind) proton source. In contrast to the magnetospheres of Jupiter and Earth, there are no lobe regions essentially devoid of particles in Saturn's nighttime magnetosphere. Electron pitch-angle distributions are generally bidirectional andfield-aligned, indicating closed field lines at high latitudes. Ions in this region are generally moving toward Saturn, while in the magnetosheath they exhibit strong antisunward streaming which is inconsistent with purely convective flows. Fluxes of magnetospheric ions downstream from the bow shock are present over distances >/= 200 Saturn radii from the planet. Novel features identified in the Saturnian magnetosphere include a mantle of low-energy particles extending inward from the dayside magnetopause to approximately 17 Saturn radii, at least two intensity dropouts occurring approximately 11 hours apart in the nighttime magnetosphere, and a pervasive population of energetic molecular hydrogen.
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Simpson JA, Bastian TS, Chenette DL, McKibben RB, Pyle KR. The trapped radiations of Saturn and their absorption by satellites and rings. ACTA ACUST UNITED AC 1980. [DOI: 10.1029/ja085ia11p05731] [Citation(s) in RCA: 99] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Van Allen JA, Randall BA, Thomsen MF. Sources and sinks of energetic electrons and protons in Saturn's magnetosphere. ACTA ACUST UNITED AC 1980. [DOI: 10.1029/ja085ia11p05679] [Citation(s) in RCA: 93] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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