Publications (3)0 Total impact
-
[show abstract]
[hide abstract]
ABSTRACT: Ion phase densities of Neptune are presently ascertained at the first and second adiabatic invariants of charged-particle motion on the basis of an analysis of Voyager 2 measurements. The profiles thus obtained are interpreted as indicative of generally inward radial diffusion, with an energetic ion source near L = 10. Excellent agreement is obtained between inbound and outbound phase-space density profiles at the values of the invariants; this suggests approximately axisymmetric, quasi-stationary radiation belts. The inward diffusing power carried by energetic ions appears adequate for powering Neptune's aurora, if enough of the ions are lost to the Neptune atmosphere.
11/1992;
-
[show abstract]
[hide abstract]
ABSTRACT: The energetic particle measurements by the low-energy charged-particle and cosmic-ray instruments on the Voyager 2 spacecraft in the magnetosphere of Uranus are reviewed. Upstream events were observed outside the Uranian bow shock, probably produced by ion escape from the magnetosphere. Evidence of earthlike substorm activity was discovered within the Uranian magnetosphere. A proton injection event was observed within the orbit of Umbriel and proton events were observed in the magnetotail plasma-sheet boundary layer that are diagnostic of earthlike substorms. The magnetospheric composition is totally dominated by protons, with only a trace abundance of H(2+) and no evidence for He or heavy ions; the Uranian atmophere is argued to be the principal plasma source. Phase-space densities of medium energy protons show inward radial diffusion and are quantitatively similar to those observed at the earth, Jupiter, and Saturn. These findings and plasma wave data suggest the existence of structures analogous to the earth's plasmasphere and plasmapause.
02/1991;
-
[show abstract]
[hide abstract]
ABSTRACT: Ion intensities measured by the Voyager 2 Low Energy Charged Particle (LECP) experiment at Neptune have been analyzed to determine ion phase space densities at fixed values of the first and second adiabatic invariants of charged particle motion. The phase space densities are broadly peaked near L = 10 and generally show a rapid decline going toward Neptune, although there is a gap in data coverage at the Proteus (1989N1) minimum L-shell. These profiles are interpreted as indicating generally inward radial diffusion with an energetic ion source near L = 10. There is excellent agreement between inbound and outbound phase space density profiles at the same values of the invariants, suggesting quasistationary and roughly axisymmetric radiation belts. If absorption by Neptune's moons and rings is an important loss process, then the radial diffusion coefficient DLL is on the order of 10−7L3 sec−1, consistent with the Voyager Plasma Science determination for a Triton-associated proton source of 1025 sec−1. The LECP ion phase space density profiles are consistent with relatively weak L-dependence of DLL, provided that loss rates increase toward the planet; for an extreme case of a loss rate independent of L, DLL ∝ L6.03. Weaker L dependence of DLL is found for a loss rate τ−1 increasing toward the planet (DLL ∝ L3 when τ−1 ∝ L−3.63), suggesting interchange diffusion. With DLL = 6 × 10−8L3 sec−1, the inward diffusing power carried by energetic ions is estimated as 2 × 109 W, which would be adequate to power Neptune's aurora if a substantial portion of the ions is lost into Neptune's atmosphere.
Icarus.
