Experiments on dust transport in plasma to investigate the origin of the lunar horizon glow

Dust grains on the lunar surface are exposed to UV radiation and solar wind plasma and can collect electrical charges, leading to their possible lift‐off and transport in the presence of near‐surface electric fields. Motivated by the long‐standing open questions about the physics of electrostatic lunar dust transport, we investigated the dynamics of dust grains on a conducting surface in a laboratory plasma. The dust used in these experiments was a nonconducting JSC‐Mars‐1 sample with particle size of less than 25 microns. We found that dust grains placed on a conducting surface, which is biased more negatively than its floating potential, charge positively, and an initial pile spreads to form a dust ring. Dust particles were observed to land on insulating blocks, indicating the height of their hopping motion. The measured electrostatic potential distribution above the dust pile shows that an outward pointing electric field near the edge of the pile is responsible for spreading the positively charged grains. A nonmonotonic potential dip was measured in the sheath above an insulating patch, indicating a localized upward electric field causing the dust lift‐off from the surface. Faraday cup measurements showed that the grains near the boundary of the dust pile collect more charge than those closer to the center of the dust pile and can be more readily lifted and moved in the radial direction, leading to the formation of a spreading ring.