THEORETICAL INVESTIGATION OF ELECTROSTATIC AND ELECTROMAGNETIC WAVE PROPAGATION AND INSTABILITIES IN DUSTY PLASMA WITH DUST CHARGE FLUCTUATIONS

Abstract

Astrophysical dust occurs in many circumstances, like interstellar and circumstellar media, and between and around planets and comets. Typical Solar System applications include planetary rings, asteroid zones, cometary comae and tails, and regions of Earth's lower magnetosphere. Dust grains immersed in ambient plasmas are electrically charged by various processes and interact with electromagnetic fields. Intriguing phenomena observed in the 1980s by Voyager cameras and attributed to charged dust are radial spokes in the B-ring and braids in the F-ring of Saturn. Collective effects become important when the dust intergrain distance is smaller than the plasma Debye length, and start from observations that micron-sized dust grains can have very high negative charges and in proportion even higher masses. Characteristic dust frequencies are considerably smaller than corresponding electron or ion quantities, giving rise to new low-frequency eigenmodes, which could explain some of the low-frequency noise in space and astrophysical plasmas. Repelling electrostatic forces between charged dust grains prevent planetary rings from collapsing to very thin sheets, and oscillations in transverse ring thickness give rise to resonant phenomena, held responsible for gaps in the rings of Jupiter and Saturn. Further features are connected with fluctuating dust charges, which imply highly nontrivial source and/or sink terms in the description, and those in turn lead to new electrostatic and electromagnetic instabilities. Many different papers are reviewed which discuss waves and instabilities in dusty space plasmas, both with fixed and variable dust charges, at the linear level and, at the nonlinear level, involving double layers, solitons, vortices and other waves. These studies are at present far ahead of what observations can corroborate, a situation not likely to change soon due to the paucity of coming solar system missions concerned with planetary or cometary phenomena.