Showing papers by "Eberhard Grün published in 1987"
TL;DR: In this paper, the cloud potential V and dust potential U in dusty clouds are calculated for two limiting theoretical cases between which actual cases are expected to exist, and the results show that the values of V and U are strongly dependent on the character of the internal plasma and that, most of the time during which internal plasma retains its non-Maxwellian character, the creation of double layers and the occurrence of transitions with considerable readjustments of the cloud structure are possible.
Abstract: The cloud potential V and dust potential U in dusty clouds are calculated for two limiting theoretical cases between which actual cases are expected to exist. In one case particles are not thermalized within the cloud, and in the other the plasma is thermalized in the cloud interior to form a Maxwellian plasma with densities given by Boltzmann relations as functions of the local cloud potential. The results show that the values of V and U are strongly dependent on the character of the internal plasma and that, most of the time during which the internal plasma retains its non-Maxwellian character, the creation of double layers and the occurrence of transitions with considerable readjustments of the cloud structure are possible. Such processes should not occur if the internal plasma is thermalized.
203 citations
TL;DR: The characteristics and distribution of the small particles detected by the plasma-wave and radio-astronomy instruments during the Voyager 2 encounter with Uranus in January 1986 are examined in this paper.
Abstract: The characteristics and distribution of the small particles detected by the plasma-wave and radio-astronomy instruments during the Voyager 2 encounter with Uranus in January 1986 are examined. The nature of the observational data and the analysis techniques employed are discussed, and the results are presented in graphs. Particles of rms mass about 2.6 ng and radii of a few microns were found in an impact region of thickness 3840 km, with a maximum number density of 1600/cu m about 280 km from the equatorial plane, shortly after Voyager 2 crossed the plane of the Uranian rings. The possible origin of the particles in the rings or in small satellites outside the rings is considered.
63 citations
Journal Article•
TL;DR: In this article, Giotto, Vega-1 and Vega-2 have been bombarded by a flow of gas and dust particles during their flyby of comet Halley, and the emission of secondary electrons and sputtered ions caused by the large impact velocities perturbed the plasma density in the spacecraft vicinity and was a possible source of interference for electric field and plasma measurements.
Abstract: Giotto, Vega-1 and Vega-2 have been bombarded by a flow of gas and dust particles during their flyby of comet Halley. The emission of secondary electrons and sputtered ions caused by the large impact velocities (70–80 km s −1) perturbed the plasma density in the spacecraft vicinity and was a possible source of interference for electric field and plasma measurements. Identical impact plasma detectors were mounted on the three space probes; the saturation currents of secondary electrons emitted from gold targets were measured once per second. The results obtained during the three flybys are presented and compared. Information about the gas density profile and nucleus gas production rate can be derived from the measurements.
11 citations