MAGNETICALLY ENHANCED COAGULATION OF VERY SMALL IRON GRAINS

Laboratory experiments, in which very small (approximately 20 nm) grai ns are produced in the presence of a magnetic field on the order of 10 0 Gauss in a low-pressure hydrogen atmosphere, have demonstrated that such smokes can become permanently magnetized. We show that magnetizat ion results in an enormous enhancement in the coagulation efficiency o f such materials even in the absence of external magnetic fields. Smal l iron grains should have been produced in the solar nebula by thermal processing of preexisting interstellar grains. If such processing occ urred via high-energy electromagnetic events then the resultant magnet ized grains could have triggered the formation of centimeter- to meter -sized protoplanetessimals by acting as ''nets'' capable of sweeping u p nonconductive silicates suspended in the gas. It is possible that th e presence of conductive fractal aggregates observed in modem-day prot ostellar disks could be explained by the enhanced coagulation efficien cy of very small magnetized iron particles. (C) 1994 Academic Press, I nc.