Lunar dust charging by photoelectric emissions

Abstract

The lunar surface is covered with a thick layer of sub-micron/micron size dust grains formed by meteoritic impact over billions of years. The fine dust grains are levitated and transported on the lunar surface, as indicated by the transient dust clouds observed over the lunar horizon during the Apollo 17 mission. Theoretical models suggest that the dust grains on the lunar surface are charged by the solar UV radiation as well as the solar wind. Even without any physical activity, the dust grains are levitated by electrostatic fields and transported away from the surface in the near vacuum environment of the Moon. The current dust charging and levitation models, however, do not fully explain the observed phenomena. Since the abundance of dust on the Moon's surface with its observed adhesive characteristics has the potential of severe impact on human habitat and operations and lifetime of a variety of equipment, it is necessary to investigate the charging properties and the lunar dust phenomena in order to develop appropriate mitigating strategies.Photoelectric emission induced by the solar UV radiation with photon energies higher than the work function of the grain materials is recognized to be the dominant process for charging of the lunar dust, and requires measurements of the photoelectric yields to determine the charging and equilibrium potentials of individual dust grains. In this paper, we present the first laboratory measurements of the photoelectric efficiencies and yields of individual submicron/micron size dust grains selected from sample returns of Apollo 17, and Luna 24 missions, as well as similar size dust grains from the JSC-1 simulants. The measurements were made on a laboratory facility based on an electrodynamic balance that permits a variety of experiments to be conducted on individual sub-micron/micron size dust grains in simulated space environments. The photoelectric emission measurements indicate grain size dependence 2 with the yield increasing by an order of magnitude for grains of sub-micron to several micron size radii, at which it reaches asymptotic values. The yield for large size grains is found to be more than an order of magnitude higher than the bulk measurements on lunar fines reported in the literature.

Plasma heat pump and heat engine

“…Particles may be injected by a suitable designed pressure impulse particle injector. 27 One of the problems faced in handling submicron sized particles is that they tend to coagulate and form clumps. This problem may be avoided by mixing them in distilled water and injecting a small portion of this solution.…”

Electrical Charging of Volcanic Plumes

“…On the Moon, photoelectric charging and bombardment charging by the solar wind is significant and is inferred to be responsible for the electrostatic levitation of dust particles from the surface (Abbas et al 2007, and references therein). Similarly for dusts in space, consideration of these processes is an integral part in understanding the relevant dynamics (Graps and Jones 2008;Horányi 1996).…”

Influence of Back Electrostatic Field on the Collection Efficiency of an Electrostatic Lunar Dust Collector

“…A cloud of levitated lunar grains with high affinity of adhering to the nearby surfaces, which hampered the lunar surface operations, was observed during the entire Apollo program (from 1969 to 1973) (Gaier, 2005;Stubbs et al, 2006;Colwell et al, 2009;Gaier et al, 2011). Due to the rarefied atmosphere of the moon and absence of a strong magnetic field, the lunar surface is not shielded from high energetic solar radiation and solar winds (Abbas et al, 2007;Colwell et al, 2009;Calle et al, 2011). While photoemissive radiation (e.g., UV and X-ray) on lunar dayside accumulate positive charges, impingement of electrons on lunar nightside leads to negative charge accumulation on lunar grains (Walch et al, 1995;Halekas et al, 2002;Halekas et al, 2008;Dove et al, 2010).…”