Micrometeorite erosion of the main rings as a source of plasma in the inner Saturnian plasma torus

Pospieszalska, M. K.; Johnson, R. E.

doi:10.1016/0019-1035(91)90162-m

Cited by 45 publications

(35 citation statements)

References 25 publications

(33 reference statements)

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“…Rather, >10 keV plasma-ion sputtering of the large icy satellites Tethys, Dione, and Rhea (Cheng and Lanzerotti 1978, Eviatar 1984, Johnson et al 1989 and micrometeorite vaporization of the main ring particles (Pospieszalska and Johnson 1991) were proposed as the dominant sources. However, the direct observation of neutral OH (Shemansky et al 1993) gave an OH concentration in the ring plane of 170 cm −3 , much larger than predicted.…”

Section: Sources Of Neutralsmentioning

confidence: 99%

Saturn's E Ring and Production of the Neutral Torus

Jurač

2001

Icarus

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Section: Sources Of Neutralsmentioning

confidence: 99%

Saturn's E Ring and Production of the Neutral Torus

Jurač

2001

Icarus

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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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“…The north-south distribution of this current will then be determined by the distribution of the neutral species (derived from plasma sputtering of icy moons and micrometeorite erosion of ring grains), which is believed to be tightly confined within ∼0.5-1 R S of the equatorial plane (e.g. Johnson et al, 1989;Pospieszalska and Johnson, 1991;Richardson et al, 1998). It can be seen from the figures that Voyager-1 was continuously located south of this plasma sheet for a considerable interval (∼10 h) around closest approach, before passing northward through the plasma sheet on its outbound pass, while Voyager-2 passed from the region north of the plasma sheet on its inbound pass, through the plasma sheet near closest approach, and then through the region south of the plasma sheet outbound.…”

Section: Spacecraft Trajectoriesmentioning

confidence: 99%

Azimuthal magnetic fields in Saturn’s magnetosphere: effects associated with plasma sub-corotation and the magnetopause-tail current system

2003

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Abstract. We calculate the azimuthal magnetic fields expected to be present in Saturn's magnetosphere associated with two physical effects, and compare them with the fields observed during the flybys of the two Voyager spacecraft. The first effect is associated with the magnetosphereionosphere coupling currents which result from the subcorotation of the magnetospheric plasma. This is calculated from empirical models of the plasma flow and magnetic field based on Voyager data, with the effective Pedersen conductivity of Saturn's ionosphere being treated as an essentially free parameter. This mechanism results in a 'lagging' field configuration at all local times. The second effect is due to the day-night asymmetric confinement of the magnetosphere by the solar wind (i.e. the magnetopause and tail current system), which we have estimated empirically by scaling a model of the Earth's magnetosphere to Saturn. This effect produces 'leading' fields in the dusk magnetosphere, and 'lagging' fields at dawn. Our results show that the azimuthal fields observed in the inner regions can be reasonably well accounted for by plasma sub-corotation, given a value of the effective ionospheric Pedersen conductivity of ∼1-2 mho. This statement applies to field lines mapping to the equator within ∼8 R S (1 R S is taken to be 60 330 km) of the planet on the dayside inbound passes, where the plasma distribution is dominated by a thin equatorial heavy-ion plasma sheet, and to field lines mapping to the equator within ∼15 R S on the dawn side outbound passes. The contributions of the magnetopause-tail currents are estimated to be much smaller than the observed fields in these regions. If, however, we assume that the azimuthal fields observed in these regions are not due to sub-corotation but to some other process, then the above effective conductivities define an upper limit, such that values above ∼2 mho can definitely be ruled out. Outside of this inner region the spacecraft observed both 'lagging' and 'leading' fields in the post-noon dayside magnetosphere during the inbound passes, with 'leading' fields being observed both adjacent to the magnetopause and in the ring current reCorrespondence to: E. J. Bunce (emma.bunce@ion.le.ac.uk) gion, and 'lagging' fields being observed between. The observed 'lagging' fields are consistent in magnitude with the sub-corotation effect with an effective ionospheric conductivity of ∼1-2 mho, while the 'leading' fields are considerably larger than those estimated for the magnetopause-tail currents, and appear to be indicative of the presence of another dynamical process. No 'leading' fields were observed outside the inner region on the dawn side outbound passes, with the azimuthal fields first falling below those expected for sub-corotation, before increasing, to exceed these values at radial distances beyond ∼15-20 R S , where the effect of the magnetopause-tail currents becomes significant. As a by-product, our investigation also indicates that modification and scaling of terrestrial magnetic field ...

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Micrometeorite erosion of the main rings as a source of plasma in the inner Saturnian plasma torus

Cited by 45 publications

References 25 publications

Saturn's E Ring and Production of the Neutral Torus

Saturn's E Ring and Production of the Neutral Torus

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

Azimuthal magnetic fields in Saturn’s magnetosphere: effects associated with plasma sub-corotation and the magnetopause-tail current system

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