The neutral cloud and heavy ion inner torus at Saturn

Johnson, R. E.; Pospieszalska, M. K.; Sittler, E. C.; Cheng, A. F.; Lanzerotti, L. J.; Sieveka, Edwin M.

doi:10.1016/0019-1035(89)90092-4

Cited by 83 publications

(72 citation statements)

References 52 publications

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“…If oxygen dominates then a temperature of -80 keV is appropriate. Inside the orbit of Dione, T±/TII ~5 (Richardson and Eviatar 1988, Richardson and Sittier 1988) for the cold component as the equilibration processes are slow (e.g., Cheng 1986, Johnson et al 1988b. For the calculations at Dione we use 3' -= 2 (T~/TII ~-2) for both components and discuss the effect or changes in 3".…”

Section: Results: Dionementioning

confidence: 99%

“…The cold and hot components of the plasma surrounding Dione are seen to give very different bombardment distributions. Johnson et al (1988b) have shown that the morphology of the cloud of neutral molecules which co-orbit with the satellites and, hence, the distribution of new heavy ions, is sensitive to the ion bombardment profile. As the u- • .…”

Section: Results: Dionementioning

confidence: 99%

“…These heavy ions sputter the surfaces of the icy satellites ) producing a cloud of neutral molecules (Cheng et al 1986, Johnson et al 1988b which are ionized and swept up by the rotating magnetic fields. The newly created ions then become a component of the plasma ion torus and these in turn bombard the satellite surfaces.…”

Section: Introductionmentioning

confidence: 99%

“…The newly created ions then become a component of the plasma ion torus and these in turn bombard the satellite surfaces. Therefore, the spatial distribution of ejected neutrals and spatial distribution of plasma in the torus are closely coupled (Johnson et al 1988b). The spatial distribution of ejected neutrals is also dependent on the pattern of ion bombardment of satellite surfaces (Johnson et al 1978b).…”

Section: Introductionmentioning

confidence: 99%

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Magnetospheric ion bombardment profiles of satellites: Europa and Dione

Pospieszalska

Johnson

1989

Icarus

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108

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Section: Results: Dionementioning

confidence: 99%

Section: Results: Dionementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Magnetospheric ion bombardment profiles of satellites: Europa and Dione

Pospieszalska

Johnson

1989

Icarus

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108

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“…The physics of this region is dominated by plasma production and pick-up from neutral gas sources originating from ring grains and the icy surfaces of moons, followed by centrifugally-driven outward radial transport associated with small-scale motions not illustrated in the figure (e.g. Johnson et al, 1989;Pospieszalska and Johnson, 1991;Richardson, 1992;Richardson et al, 1998). No detailed self-consistent dynamical models of these processes have yet been proposed for Saturn as they have for Jupiter (e.g.…”

Section: Equatorial Flowsmentioning

confidence: 99%

Saturn's polar ionospheric flows and their relation to the main auroral oval

2004

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Abstract. We consider the flows and currents in Saturn's polar ionosphere which are implied by a three-component picture of large-scale magnetospheric flow driven both by planetary rotation and the solar wind interaction. With increasing radial distance in the equatorial plane, these components consist of a region dominated by planetary rotation where planetary plasma sub-corotates on closed field lines, a surrounding region where planetary plasma is lost down the dusk tail by the stretching out of closed field lines followed by plasmoid formation and pinch-off, as first described for Jupiter by Vasyliunas, and an outer region driven by the interaction with the solar wind, specifically by reconnection at the dayside magnetopause and in the dawn tail, first discussed for Earth by Dungey. The sub-corotating flow on closed field lines in the dayside magnetosphere is constrained by Voyager plasma observations, showing that the plasma angular velocity falls to around half of rigid corotation in the outer magnetosphere, possibly increasing somewhat near the dayside magnetopause, while here we provide theoretical arguments which indicate that the flow should drop to considerably smaller values on open field lines in the polar cap. The implied ionospheric current system requires a four-ring pattern of field-aligned currents, with distributed downward currents on open field lines in the polar cap, a narrow ring of upward current near the boundary of open and closed field lines, and regions of distributed downward and upward current on closed field lines at lower latitudes associated with the transfer of angular momentum from the planetary atmosphere to the sub-corotating planetary magnetospheric plasma. Recent work has shown that the upward current associated with sub-corotation is not sufficiently intense to produce significant auroral acceleration and emission. Here we suggest that the observed auroral oval at Saturn instead corresponds to the ring of upward current bounding the region of open and closed field lines. Estimates indicate that auroras of brightness from a few kR to a few tens of kR can be produced byCorrespondence to: S. W. H. Cowley (swhc1@ion.le.ac.uk) precipitating accelerated magnetospheric electrons of a few keV to a few tens of keV energy, if the current flows in a region which is sufficiently narrow, of the order of or less than ∼1000 km (∼1 • latitude) wide. Arguments are also given which indicate that the auroras should typically be significantly brighter on the dawn side of the oval than at dusk, by roughly an order of magnitude, and should be displaced somewhat towards dawn by the down-tail outflow at dusk associated with the Vasyliunas cycle. Model estimates are found to be in good agreement with data derived from high quality images newly obtained using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, both in regard to physical parameters, as well as local time effects. The implication of this picture is that the form, position, and brightness of Saturn's main auroral o...

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