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Cohen IJ, Smith EJ, Clark GB, Turner DL, Ellison DH, Clare B, Regoli LH, Kollmann P, Gallagher DT, Holtzman GA, Likar JJ, Morizono T, Shannon M, Vodusek KS. Plasma Environment, Radiation, Structure, and Evolution of the Uranian System (PERSEUS): A Dedicated Orbiter Mission Concept to Study Space Physics at Uranus. SPACE SCIENCE REVIEWS 2023; 219:65. [PMID: 37869526 PMCID: PMC10587260 DOI: 10.1007/s11214-023-01013-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/14/2023] [Accepted: 10/05/2023] [Indexed: 10/24/2023]
Abstract
The Plasma Environment, Radiation, Structure, and Evolution of the Uranian System (PERSEUS) mission concept defines the feasibility and potential scope of a dedicated, standalone Heliophysics orbiter mission to study multiple space physics science objectives at Uranus. Uranus's complex and dynamic magnetosphere presents a unique laboratory to study magnetospheric physics as well as its coupling to the solar wind and the planet's atmosphere, satellites, and rings. From the planet's tilted and offset, rapidly-rotating non-dipolar magnetic field to its seasonally-extreme interactions with the solar wind to its unexpectedly intense electron radiation belts, Uranus hosts a range of outstanding and compelling mysteries relevant to the space physics community. While the exploration of planets other than Earth has largely fallen within the purview of NASA's Planetary Science Division, many targets, like Uranus, also hold immense scientific value and interest to NASA's Heliophysics Division. Exploring and understanding Uranus's magnetosphere is critical to make fundamental gains in magnetospheric physics and the understanding of potential exoplanetary systems and to test the validity of our knowledge of magnetospheric dynamics, moon-magnetosphere interactions, magnetosphere-ionosphere coupling, and solar wind-planetary coupling. The PERSEUS mission concept study, currently at Concept Maturity Level (CML) 4, comprises a feasible payload that provides closure to a range of space physics science objectives in a reliable and mature spacecraft and mission design architecture. The mission is able to close using only a single Mod-1 Next-Generation Radioisotope Thermoelectric Generator (NG-RTG) by leveraging a concept of operations that relies of a significant hibernation mode for a large portion of its 22-day orbit.
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Affiliation(s)
- Ian J Cohen
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD USA
| | - Evan J Smith
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD USA
| | - George B Clark
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD USA
| | - Drew L Turner
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD USA
| | - Donald H Ellison
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD USA
| | - Ben Clare
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD USA
| | - Leonardo H Regoli
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD USA
| | - Peter Kollmann
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD USA
| | | | - G Allan Holtzman
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD USA
| | - Justin J Likar
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD USA
| | - Takeshi Morizono
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD USA
| | - Matthew Shannon
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD USA
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Aizawa S, Harada Y, André N, Saito Y, Barabash S, Delcourt D, Sauvaud JA, Barthe A, Fedorov A, Penou E, Yokota S, Miyake W, Persson M, Nénon Q, Rojo M, Futaana Y, Asamura K, Shimoyama M, Hadid LZ, Fontaine D, Katra B, Fraenz M, Krupp N, Matsuda S, Murakami G. Direct evidence of substorm-related impulsive injections of electrons at Mercury. Nat Commun 2023; 14:4019. [PMID: 37463887 DOI: 10.1038/s41467-023-39565-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2023] [Accepted: 06/14/2023] [Indexed: 07/20/2023] Open
Abstract
Mercury's magnetosphere is known to involve fundamental processes releasing particles and energy like at Earth due to the solar wind interaction. The resulting cycle is however much faster and involves acceleration, transport, loss, and recycling of plasma. Direct experimental evidence for the roles of electrons during this cycle is however missing. Here we show that in-situ plasma observations obtained during BepiColombo's first Mercury flyby reveal a compressed magnetosphere hosts of quasi-periodic fluctuations, including the original observation of dynamic phenomena in the post-midnight, southern magnetosphere. The energy-time dispersed electron enhancements support the occurrence of substorm-related, multiple, impulsive injections of electrons that ultimately precipitate onto its surface and induce X-ray fluorescence. These observations reveal that electron injections and subsequent energy-dependent drift now observed throughout Solar System is a universal mechanism that generates aurorae despite the differences in structure and dynamics of the planetary magnetospheres.
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Affiliation(s)
- Sae Aizawa
- IRAP, CNRS-UPS-CNES, Toulouse, France.
- Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan.
- Department of Physics, University of Pisa, Pisa, Italy.
| | - Yuki Harada
- Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto, Japan
| | | | - Yoshifumi Saito
- Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan
| | - Stas Barabash
- Swedish Institute of Space Physics, Kiruna, SE 98192, Sweden
| | - Dominique Delcourt
- Laboratoire de Physique des Plasmas (LPP), CNRS-Observatoire de Paris-Sorbonne Université-Université Paris Saclay-Ecole polytechnique-Institut Polytechnique de Paris, 91120, Palaiseau, France
| | | | | | | | | | - Shoichiro Yokota
- Department of Earth and Space Science, Graduate School of Science, Osaka University, Osaka, Japan
| | | | - Moa Persson
- IRAP, CNRS-UPS-CNES, Toulouse, France
- Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Japan
| | | | | | | | - Kazushi Asamura
- Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan
| | | | - Lina Z Hadid
- Laboratoire de Physique des Plasmas (LPP), CNRS-Observatoire de Paris-Sorbonne Université-Université Paris Saclay-Ecole polytechnique-Institut Polytechnique de Paris, 91120, Palaiseau, France
| | - Dominique Fontaine
- Laboratoire de Physique des Plasmas (LPP), CNRS-Observatoire de Paris-Sorbonne Université-Université Paris Saclay-Ecole polytechnique-Institut Polytechnique de Paris, 91120, Palaiseau, France
| | - Bruno Katra
- Laboratoire de Physique des Plasmas (LPP), CNRS-Observatoire de Paris-Sorbonne Université-Université Paris Saclay-Ecole polytechnique-Institut Polytechnique de Paris, 91120, Palaiseau, France
| | - Markus Fraenz
- Max Planck Institute for Solar System Research, Göttingen, Germany
| | - Norbert Krupp
- Max Planck Institute for Solar System Research, Göttingen, Germany
| | | | - Go Murakami
- Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan
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Styczinski MJ, Vance SD, Harnett EM, Cochrane CJ. A perturbation method for evaluating the magnetic field induced from an arbitrary, asymmetric ocean world analytically. ICARUS 2022; 376:114840. [PMID: 35140451 PMCID: PMC8819682 DOI: 10.1016/j.icarus.2021.114840] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Magnetic investigations of icy moons have provided some of the most compelling evidence available confirming the presence of subsurface, liquid water oceans. In the exploration of ocean moons, especially Europa, there is a need for mathematical models capable of predicting the magnetic fields induced under a variety of conditions, including in the case of asymmetric oceans. Existing models are limited to either spherical symmetry or assume an ocean with infinite conductivity. In this work, we use a perturbation method to derive a semi-analytic result capable of determining the induced magnetic moments for an arbitrary layered body, provided each layer is nearly spherical. Crucially, we find that degree-2 tidal deformation results in changes to the induced dipole moments. We demonstrate application of our results to models of plausible asymmetry from the literature within the oceans of Europa and Miranda and the ionospheres of Callisto and Triton. For the models we consider, we find that in the asymmetric case, the induced magnetic field differs by more than 2 nT near the surface of Europa, 0.25-0.5 nT at 1 R above Miranda and Triton, and is essentially unchanged for Callisto. For Miranda and Triton, this difference is as much as 20%-30% of the induced field magnitude. If measurements near the moons can be made precisely to better than a few tenths of a nT, these values may be used by future spacecraft investigations to characterize asymmetry within the interior of icy moons.
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Affiliation(s)
- Marshall J. Styczinski
- Department of Physics, University of Washington, Box 351560, 3910 15th Ave NE, Seattle, WA 98195-1560, USA
- UW Astrobiology Program, University of Washington, Box 351580, 3910 15th Ave NE, Seattle, WA 98195-1580, USA
| | - Steven D. Vance
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA 91109-8001, USA
| | - Erika M. Harnett
- UW Astrobiology Program, University of Washington, Box 351580, 3910 15th Ave NE, Seattle, WA 98195-1580, USA
- Department of Earth and Space Sciences, University of Washington, Box 351310, 4000 15th Ave NE, Seattle, WA 98195-1310, USA
| | - Corey J. Cochrane
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA 91109-8001, USA
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Paty C, Arridge CS, Cohen IJ, DiBraccio GA, Ebert RW, Rymer AM. Ice giant magnetospheres. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2020; 378:20190480. [PMID: 33161869 DOI: 10.1098/rsta.2019.0480] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 09/16/2020] [Indexed: 05/20/2023]
Abstract
The ice giant planets provide some of the most interesting natural laboratories for studying the influence of large obliquities, rapid rotation, highly asymmetric magnetic fields and wide-ranging Alfvénic and sonic Mach numbers on magnetospheric processes. The geometries of the solar wind-magnetosphere interaction at the ice giants vary dramatically on diurnal timescales due to the large tilt of the magnetic axis relative to each planet's rotational axis and the apparent off-centred nature of the magnetic field. There is also a seasonal effect on this interaction geometry due to the large obliquity of each planet (especially Uranus). With in situ observations at Uranus and Neptune limited to a single encounter by the Voyager 2 spacecraft, a growing number of analytical and numerical models have been put forward to characterize these unique magnetospheres and test hypotheses related to the magnetic structures and the distribution of plasma observed. Yet many questions regarding magnetospheric structure and dynamics, magnetospheric coupling to the ionosphere and atmosphere, and potential interactions with orbiting satellites remain unanswered. Continuing to study and explore ice giant magnetospheres is important for comparative planetology as they represent critical benchmarks on a broad spectrum of planetary magnetospheric interactions, and provide insight beyond the scope of our own Solar System with implications for exoplanet magnetospheres and magnetic reversals. This article is part of a discussion meeting issue 'Future exploration of ice giant systems'.
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Affiliation(s)
- Carol Paty
- Department of Earth Sciences, University of Oregon, 100 Cascade Hall, Eugene, OR 97403-1272, USA
| | - Chris S Arridge
- Department of Physics, Lancaster University, Bailrigg, Lancaster LA1 4YW, UK
| | - Ian J Cohen
- The Johns Hopkins University Applied Physics Laboratory, 11000 Johns Hopkins Road, Laurel, MD 20723, USA
| | - Gina A DiBraccio
- Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
| | - Robert W Ebert
- Department of Space Research, Southwest Research Institute, San Antonio, TX 78228-0510, USA
- Department of Physics and Astronomy, University of Texas, San Antonio, TX 78249-0600, USA
| | - Abigail M Rymer
- The Johns Hopkins University Applied Physics Laboratory, 11000 Johns Hopkins Road, Laurel, MD 20723, USA
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Lamy L. Auroral emissions from Uranus and Neptune. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2020; 378:20190481. [PMID: 33161867 PMCID: PMC7658782 DOI: 10.1098/rsta.2019.0481] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 09/14/2020] [Indexed: 05/20/2023]
Abstract
Uranus and Neptune possess highly tilted/offset magnetic fields whose interaction with the solar wind shapes unique twin asymmetric, highly dynamical, magnetospheres. These radiate complex auroral emissions, both reminiscent of those observed at the other planets and unique to the ice giants, which have been detected at radio and ultraviolet (UV) wavelengths to date. Our current knowledge of these radiations, which probe fundamental planetary properties (magnetic field, rotation period, magnetospheric processes, etc.), still mostly relies on Voyager 2 radio, UV and in situ measurements, when the spacecraft flew by each planet in the 1980s. These pioneering observations were, however, limited in time and sampled specific solar wind/magnetosphere configurations, which significantly vary at various timescales down to a fraction of a planetary rotation. Since then, despite repeated Earth-based observations at similar and other wavelengths, only the Uranian UV aurorae have been re-observed at scarce occasions by the Hubble Space Telescope. These observations revealed auroral features radically different from those seen by Voyager 2, diagnosing yet another solar wind/magnetosphere configuration. Perspectives for the in-depth study of the Uranian and Neptunian auroral processes, with implications for exoplanets, include follow-up remote Earth-based observations and future orbital exploration of one or both ice giant planetary systems. This article is part of a discussion meeting issue 'Future exploration of ice giant systems'.
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Affiliation(s)
- L. Lamy
- LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France
- LAM, Pythéas, Aix Marseille Université, CNRS, CNES, 38 Rue Frédéric Joliot Curie, 13013 Marseille, France
- e-mail:
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Livadiotis G. Nonextensive Statistical Mechanics: Equivalence Between Dual Entropy and Dual Probabilities. ENTROPY 2020; 22:e22060594. [PMID: 33286366 PMCID: PMC7517129 DOI: 10.3390/e22060594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/13/2020] [Revised: 05/20/2020] [Accepted: 05/21/2020] [Indexed: 11/27/2022]
Abstract
The concept of duality of probability distributions constitutes a fundamental “brick” in the solid framework of nonextensive statistical mechanics—the generalization of Boltzmann–Gibbs statistical mechanics under the consideration of the q-entropy. The probability duality is solving old-standing issues of the theory, e.g., it ascertains the additivity for the internal energy given the additivity in the energy of microstates. However, it is a rather complex part of the theory, and certainly, it cannot be trivially explained along the Gibb’s path of entropy maximization. Recently, it was shown that an alternative picture exists, considering a dual entropy, instead of a dual probability. In particular, the framework of nonextensive statistical mechanics can be equivalently developed using q- and 1/q- entropies. The canonical probability distribution coincides again with the known q-exponential distribution, but without the necessity of the duality of ordinary-escort probabilities. Furthermore, it is shown that the dual entropies, q-entropy and 1/q-entropy, as well as, the 1-entropy, are involved in an identity, useful in theoretical development and applications.
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Affiliation(s)
- George Livadiotis
- Division of Space Science and Engineering, Southwest Research Institute, San Antonio, TX 78238, USA
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7
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Kappa Distributions: Statistical Physics and Thermodynamics of Space and Astrophysical Plasmas. UNIVERSE 2018. [DOI: 10.3390/universe4120144] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Kappa distributions received impetus as they provide efficient modelling of the observed particle distributions in space and astrophysical plasmas throughout the heliosphere. This paper presents (i) the connection of kappa distributions with statistical mechanics, by maximizing the associated q-entropy under the constraints of the canonical ensemble within the framework of continuous description; (ii) the derivation of q-entropy from first principles that characterize space plasmas, the additivity of energy, and entropy; and (iii) the derivation of the characteristic first order differential equation, whose solution is the kappa distribution function.
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Mauk BH. Comparative investigation of the energetic ion spectra comprising the magnetospheric ring currents of the solar system. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2014; 119:9729-9746. [PMID: 26167438 PMCID: PMC4497457 DOI: 10.1002/2014ja020392] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2014] [Accepted: 11/08/2014] [Indexed: 05/29/2023]
Abstract
Investigated here are factors that control the intensities and shapes of energetic ion spectra that make up the ring current populations of the strongly magnetized planets of the solar system, specifically those of Earth, Jupiter, Saturn, Uranus, and Neptune. Following a previous and similar comparative investigation of radiation belt electrons, we here turn our attention to ions. Specifically, we examine the possible role of the differential ion Kennel-Petschek limit, as moderated by Electromagnetic Ion Cyclotron (EMIC) waves, as a standard for comparing the most intense ion spectra within the strongly magnetized planetary magnetospheres. In carrying out this investigation, the substantial complexities engendered by the very different ion composition distributions of these diverse magnetospheres must be addressed, given that the dispersion properties of the EMIC waves are strongly determined by the ion composition of the plasmas within which the waves propagate. Chosen for comparison are the ion spectra within these systems that are the most intense observed, specifically at 100 keV and 1 MeV. We find that Earth and Jupiter are unique in having their most intense ion spectra likely limited and sculpted by the Kennel-Petschek process. The ion spectra of Saturn, Uranus, and Neptune reside far below their respective limits and are likely limited by interactions with gas and dust (Saturn) and by the absence of robust ion acceleration processes (Uranus and Neptune). Suggestions are provided for further testing the efficacy of the differential Kennel-Petschek limit for ions using the Van Allen Probes.
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Affiliation(s)
- B H Mauk
- Johns Hopkins University Applied Physics LaboratoryLaurel, Maryland, USA
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11
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Mauk B, Bagenal F. Comparative Auroral Physics: Earth and Other Planets. GEOPHYSICAL MONOGRAPH SERIES 2013. [DOI: 10.1029/2011gm001192] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
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12
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Coroniti FV, Kurth WS, Scarf FL, Krimigis SM, Kennel CF, Gurnett DA. Whistler mode emissions in the Uranian radiation belts. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja092ia13p15234] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Herbert F. The Uranian corona as a charge exchange cascade of plasma sheet protons. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/92ja02735] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Cheng AF, Krimigis SM, Mauk BH, Keath EP, Maclennan CG, Lanzerotti LJ, Paonessa MT, Armstrong TP. Energetic ion and electron phase space densities in the magnetosphere of Uranus. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja092ia13p15315] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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16
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Behannon KW, Lepping RP, Sittler EC, Ness NF, Mauk BH, Krimigis SM, McNutt RL. The magnetotail of Uranus. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja092ia13p15354] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Lanzerotti LJ, Brown WL, Maclennan CG, Cheng AF, Krimigis SM, Johnson RE. Effects of charged particles on the surfaces of the satellites of Uranus. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja092ia13p14949] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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18
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Selesnick RS, McNutt RL. Voyager 2 plasma ion observations in the magnetosphere of Uranus. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja092ia13p15249] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Affiliation(s)
- B. H. Mauk
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
| | - N. J. Fox
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
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20
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Gao S, Ho CW, Huang TS, Alexander CJ. Uranus' magnetic field and particle drifts in its inner magnetosphere. ACTA ACUST UNITED AC 1998. [DOI: 10.1029/98je00944] [Citation(s) in RCA: 5] [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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21
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Mauk BH, Gary SA, Kane M, Keath EP, Krimigis SM, Armstrong TP. Hot plasma parameters of Jupiter's inner magnetosphere. ACTA ACUST UNITED AC 1996. [DOI: 10.1029/96ja00006] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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22
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Kane M, Mauk BH, Keath EP, Krimigis SM. Hot ions in Jupiter's magnetodisc: A model for Voyager 2 low-energy charged particle measurements. ACTA ACUST UNITED AC 1995. [DOI: 10.1029/95ja00793] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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23
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Herbert F, Sandel BR. The Uranian aurora and its relationship to the magnetosphere. ACTA ACUST UNITED AC 1994. [DOI: 10.1029/93ja02673] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Selesnick RS, Stone EC. Energetic electrons at Uranus: Bimodal diffusion in a satellite limited radiation belt. ACTA ACUST UNITED AC 1991. [DOI: 10.1029/90ja02696] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Mauk BH, Keath EP, Kane M, Krimigis SM, Cheng AF, Acuña MH, Armstrong TP, Ness NF. The magnetosphere of Neptune: Hot plasmas and energetic particles. ACTA ACUST UNITED AC 1991. [DOI: 10.1029/91ja01820] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Krimigis SM, Armstrong TP, Axford WI, Bostrom CO, Cheng AF, Gloeckler G, Hamilton DC, Keath EP, Lanzerotti LJ, Mauk BH, Van Allen JA. Hot Plasma and Energetic Particles in Neptune's Magnetosphere. Science 1989; 246:1483-9. [PMID: 17756004 DOI: 10.1126/science.246.4936.1483] [Citation(s) in RCA: 92] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The low-energy charged particle (LECP) instrument on Voyager 2 measured within the magnetosphere of Neptune energetic electrons (22 kiloelectron volts </= E </= 20 megaelectron volts) and ions (28 keV </= E </= 150 MeV) in several energy channels, including compositional information at higher (>/=0.5 MeV per nucleon) energies, using an array of solid-state detectors in various configurations. The results obtained so far may be summarized as follows: (i) A variety of intensity, spectral, and anisotropy features suggest that the satellite Triton is important in controlling the outer regions of the Neptunian magnetosphere. These features include the absence of higher energy (>/=150 keV) ions or electrons outside 14.4 R(N) (where R(N) = radius of Neptune), a relative peak in the spectral index of low-energy electrons at Triton's radial distance, and a change of the proton spectrum from a power law with gamma >/= 3.8 outside, to a hot Maxwellian (kT [unknown] 55 keV) inside the satellite's orbit. (ii) Intensities decrease sharply at all energies near the time of closest approach, the decreases being most extended in time at the highest energies, reminiscent of a spacecraft's traversal of Earth's polar regions at low altitudes; simultaneously, several spikes of spectrally soft electrons and protons were seen (power input approximately 5 x 10(-4) ergs cm(-2) s(-1)) suggestive of auroral processes at Neptune. (iii) Composition measurements revealed the presence of H, H(2), and He(4), with relative abundances of 1300:1:0.1, suggesting a Neptunian ionospheric source for the trapped particle population. (iv) Plasma pressures at E >/= 28 keV are maximum at the magnetic equator with beta approximately 0.2, suggestive of a relatively empty magnetosphere, similar to that of Uranus. (v) A potential signature of satellite 1989N1 was seen, both inbound and outbound; other possible signatures of the moons and rings are evident in the data but cannot be positively identified in the absence of an accurate magnetic-field model close to the planet. Other results indude the absence of upstream ion increases or energetic neutrals [particle intensity (j) < 2.8 x 10(-3) cm(-2) s(-1) keV(-1) near 35 keV, at approximately 40 R(N)] implying an upper limit to the volume-averaged atomic H density at R </= 6 R(N) of </= 20 cm(-3); and an estimate of the rate of darkening of methane ice at the location of 1989N1 ranging from approximately 10(5) years (1-micrometer depth) to approximately 2 x 10(6) years (10-micrometers depth). Finally, the electron fluxes at the orbit of Triton represent a power input of approximately 10(9) W into its atmosphere, apparently accounting for the observed ultraviolet auroral emission; by contrast, the precipitating electron (>22 keV) input on Neptune is approximately 3 x 10(7) W, surprisingly small when compared to energy input into the atmosphere of Jupiter, Saturn, and Uranus.
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Acuña MH, Connerney JEP, Ness NF. Implications of the GSFC Q3model for trapped particle motion. ACTA ACUST UNITED AC 1988. [DOI: 10.1029/ja093ia06p05505] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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30
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Selesnick RS. Magnetospheric convection in the nondipolar magnetic field of Uranus. ACTA ACUST UNITED AC 1988. [DOI: 10.1029/ja093ia09p09607] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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