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Pressure anisotropy and radial stress balance in the Jovian neutral sheet (1991)

Krimigis, S. M. ; Mauk, B. H. ; Paranicas, C. P.

In: Other Sources

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Publikationsdatum: 2019-07-12

Beschreibung: By examining particle and magnetic field data from the Voyager 1 and 2 spacecraft, signatures were found indicating that the (greater than about 28 keV) particle pressure parallel to the magnetic field is greater than the pressure perpendicular to the field within the nightside neutral sheet (three nightside neutral sheet crossings, with favorable experimental conditions, were used). By incorporating the pressure anisotropy into the calculation of radial forces within the hightside neutral sheet, it is found that (1) force balance is approximately achieved and (2) the anisotropy force term provides the largest contribution of the other particle forces considered (pressure gradients and the corotation centrifugal force). With regard to the problem of understanding the balance of radial forces within the dayside neutral sheet (McNutt, 1984; Mauk and Krimigis, 1987), the nightside pressure anisotropy force is larger than the dayside pressure gradient forces at equivalent radial distances; however, a full accounting of the dayside regions remains to be achieved.

Schlagwort(e): LUNAR AND PLANETARY EXPLORATION

Materialart: Journal of Geophysical Research (ISSN 0148-0227); 96; 21

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2

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Satellite sweeping of energetic particles at Neptune (1991)

Cheng, A. F. ; Paranicas, C. P.

In: Other Sources

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Publikationsdatum: 2019-07-12

Beschreibung: The calculation of the absorption rate of charged particles by planetary satellites introduced by Paonessa and Cheng (1987) is generalized to include an arbitrary offset of the dipole center from the planet center, appropriate for Neptune. The absorption rates calculated for particles of fixed L shell, energy, and pitch angle reflect the features of the complicated geometry of the dipole and the moons. This absorption probability is found to be insignificant compared with that of the rings at L shells to which both sets of absorbers map. However, at larger radii the sweeping rate is controlled by the moons, and the corresponding absorption features provide a starting point for understanding the Voyager energetic particle observations.

Schlagwort(e): LUNAR AND PLANETARY EXPLORATION

Materialart: Journal of Geophysical Research Supplement (ISSN 0148-0227); 96; 19

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3

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Theory of ring sweeping of energetic particles (1991)

Cheng, A. F. ; Paranicas, C. P.

In: Other Sources

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Publikationsdatum: 2019-07-12

Beschreibung: Because the effective 'area' of the Neptunian rings is larger than that of the inner moons, the sweeping of energetic particles by the rings is perhaps the dominant process for particle loss in the magnetosphere within 5 R(N). In this paper, a theory for calculating the absorption probability of energetic charged particles by the rings is described. The effects of a large tilt and an offset between the planet and dipole centers are included. It is found that the probability of absorption for protons is so high that the sweeping lifetime is only a few times the gradient-curvature drift period. For electrons, the sweeping lifetime is even less. The pitch angle dependence for sweeping manifests itself strongly only at large equatorial pitch angles. Lower-energy particles have higher absorption rates by the rings.

Schlagwort(e): LUNAR AND PLANETARY EXPLORATION

Materialart: Journal of Geophysical Research Supplement (ISSN 0148-0227); 96; 19

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4

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Drift shells and aurora computed using the O8 magnetic field model for Neptune (1994)

Cheng, A. F. ; Paranicas, C.

In: Other Sources

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Publikationsdatum: 2019-08-28

Beschreibung: Charged particle drift shells are calculated using the O8 magnetic field model for Neptune. Inner drift shell morphologies differ significantly from dipolar drift shells for the parts of drift shells inward of r = 2 R(sub N). Outer drift shells (L approx. greater than 10), when traced down to Neptune's surface following magnetic field lines, are simple closed loops around magnetic poles. Inner drift shells (L approx. less than 4), on the other hand, when traced to the surface, are also single loops but stretched in a previously unknown way: sometimes with a cusp and sometimes into two joined loops. Inner drift shell footprints on R = 1 provide the basis for identifying precipitation L shells, interpreting observed aurora, and predicting additional emissions on that part of Neptune's surface unobserved by the Ultraviolet Spectrometer (UVS). Precipitation in a global magnetic anomaly, `ordinary' auroral precipitation near the south magnetic pole, and precipitation from field lines with no magnetic field minimum above Neptune's exobase collectively appear to account for all of the observed auroral emission regions at Neptune. To the extent that aurora can be understood in this model, it is suggested O8 may be reasonably accurate.

Schlagwort(e): SPACE SCIENCES (GENERAL)

Materialart: Journal of Geophysical Research (ISSN 0148-0227); 99; A10; p. 19,433-19,440

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5

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Ion phase space densities in the Jovian magnetosphere (1990)

Armstrong, T. P. ; Paranicas, C. P. ; Krimigis, S. M. ; [weitere]

In: Other Sources

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Publikationsdatum: 2019-08-28

Beschreibung: The Voyager Low Energy Charged Particle ion data from the Jovian magnetosphere were analyzed to determine the phase-space densities of particles in the region between 5 and 80 Jupiter radii. Data from the Jovian current sheet crossings for locally mirroring particles were used. These are the first calculations of phase-space densities in the nondipolar field region containing the Jovian magnetodisk current sheet. The profiles are consistent with lossy inward radial transport and a source in the outer magnetosphere. The inferred loss rate in a radial diffusion model measuring how quickly particles are scattered out of the neutral sheet exceeds the usual strong diffusion loss rate.

Schlagwort(e): LUNAR AND PLANETARY EXPLORATION

Materialart: Journal of Geophysical Research (ISSN 0148-0227); 95; 20833-20

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6

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The "Puck" Energetic Charged Particle Detector: Design, Heritage, and Advancements (2016)

Mitchell, D. G. ; Ho, G. C. ; Nelson, K. S. ; [weitere]

In: Other Sources

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Publikationsdatum: 2019-07-13

Beschreibung: Energetic charged particle detectors characterize a portion of the plasma distribution function that plays critical roles in some physical processes, from carrying the currents in planetary ring currents to weathering the surfaces of planetary objects. For several low-resource missions in the past, the need was recognized for a low-resource but highly capable, mass-species-discriminating energetic particle sensor that could also obtain angular distributions without motors or mechanical articulation. This need led to the development of a compact Energetic Particle Detector (EPD), known as the "Puck" EPD (short for hockey puck), that is capable of determining the flux, angular distribution, and composition of incident ions between an energy range of approximately 10 kiloelectronvolts to several megaelectronvolts. This sensor makes simultaneous angular measurements of electron fluxes from the tens of kiloelectronvolts to about 1 megaelectronvolt. The same measurements can be extended down to approximately 1 kiloelectronvolt per nucleon,with some composition ambiguity. These sensors have a proven flight heritage record that includes missions such as MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) and New Horizons, with multiple sensors on each of Juno, Van Allen Probes, and Magnetospheric Multiscale. In this review paper we discuss the Puck EPD design, its heritage, unexpected results from these past missions and future advancements. We also discuss high-voltage anomalies that are thought to be associated with the use of curved foils, which is a new foil manufacturing processes utilized on recent Puck EPD designs. Finally, we discuss the important role Puck EPDs can potentially play in upcoming missions.

Schlagwort(e): Physics of Elementary Particles and Fields; Instrumentation and Photography

Materialart: GSFC-E-DAA-TN40688 , Journal of Geophysical Research: Space Physics (ISSN 2169-9380) (e-ISSN 2169-9402); 121; 8; 7900-7913

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