Disturbances observed near Ganymede by Voyager 2
We investigated disturbances in the field and particle environment observed by Voyager 2 as it passed near the Jovian moon Ganymede in Jupiter's magnetosphere. The plasma analyzer observed at least a dozen sharply bounded depressions in density (cavities). We estimated that they probably extended at least 20 RGAMMA along the ambient magnetic field lines (R/sub G/=2635 km is the radius of Ganymede) and between 2--50 R/sub G/ in the directions transverse to B. Depressions in the magnetic field strength of the order of 5% of the ambient field strength (60nT to 135nT) were observed at the boundaries of the cavities in more than half of the cases; they were probably produced by currents flowing transverse to B on the boundaries. In some cases, the magnetic field strength inside the cavities was a few percent higher than the ambient value. This gives an upper limit on ..beta..=nkT/(B/sup 2//8..pi..) outside the cavities, viz. Beta<0.2; inmost cases ..beta.. was appreciably smaller than this. The flux of >2.5 MeV protons was strongly anti-correlated with the plasma density, the flux being higher inside the cavities than outside. One possible mechanism for the production of these flux enhancements and the cavities themselves is a local, magnetic field-aligned electric field, E. It is possible that Ganymede is responsible for the energetic protons in the cavities, in which case vertical-bar E vertical-barapprox.50 mV/m. Such a localized source implies radial motions of the magnetospheric plasma with speeds of the order of a few hundred km/s. Such motions could be produced by long-wavelength, small-amplitude Alfven waves in Jupiter's magnetosphere.
- Research Organization:
- Laboratory for Extraterrestrial Physics, NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771
- OSTI ID:
- 5320438
- Journal Information:
- Geophys. Res. Lett.; (United States), Vol. 7:1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
JUPITER PLANET
PLANETARY MAGNETOSPHERES
SATELLITES
ALFVEN WAVES
DISTURBANCES
ELECTRIC CURRENTS
ELECTRIC FIELDS
PLASMA DENSITY
VOYAGER SPACE PROBES
ATMOSPHERES
CURRENTS
HYDROMAGNETIC WAVES
PLANETARY ATMOSPHERES
PLANETS
SPACE VEHICLES
640107* - Astrophysics & Cosmology- Planetary Phenomena