Contact charging of lunar and Martian dust simulants

[1] Dusty regolith particles accumulate charge through grain-grain contact and contact with various surfaces. These processes affect vertical and horizontal transport and may cause electrical discharges in dust storms. We report the results of a simple experimental setup used to investigate the contact charging properties of two planetary analog dust samples: lunar (JSC-1) and Martian (JSC-Mars-1) regolith simulants. In these experiments, dust particles are brought into contact with various surfaces of known work functions (metals: Co, Ni, Au, Pt, and silica glass), and the resulting contact charges on the dust particles are measured. The surfaces are in the form of a thin disc mounted horizontally in a vacuum chamber. Agitation causes the dust grains to drop through a small hole into a Faraday cup, where their charge is measured. The charge on a 100 micron dust grain is typically more than 10 elementary charges and varies linearly with dust size. The measured contact charge of a dust particle increases with repeated agitation of the surface. The average contact charge also varies linearly with the work function of the contacting surface. The contact charging with oxidized metal surfaces is found to be independent of the metal’s work function. The effective work functions of the planetary analogs are determined by extrapolation to be 5.8 eV and 5.6 eV for the lunar and Martian dust simulants, respectively.