The Electrodynamics of the Moon
The Moon is often treated as an electrically simple body: an airless surface responding directly and instantaneously to solar wind forcing. Models of surface charging are built on this assumption, and engineering systems are designed around it.
This book examines in situ measurements from the Blue Ghost mission at Mare Crisium and shows that the surface does not behave as a passive boundary. The regolith enters distinct electrical states under disturbance, transitions between them, and relaxes back toward baseline on timescales that are not negligible relative to the forcing that drives them. The electrical environment is therefore time-dependent, not static.
At the grain scale, the same processes responsible for space weathering solar wind implantation, defect formation, and amorphisation produce outer rims with the physical characteristics of charge-retaining dielectric layers. These rims, long used as a record of surface exposure, may also act as the physical basis for electrical memory in the regolith. This implies that regolith maturity is not only an optical and chemical parameter, but also an electrical one, with direct influence on relaxation timescale and surface response.
The behaviour observed is consistent with a path dependent system in which the present electrical state reflects both current solar wind conditions and accumulated structural history. The short timescale dynamics captured in surface measurements and the long-timescale evolution recorded in grain rims are treated here as different expressions of the same underlying interaction.
The implications are both practical and scientific. Electrical conditions at a landing site cannot be characterised by a single measurement under quiet conditions. They vary with solar activity, material properties, and surface maturity. Systems designed for the lunar surface, power, sensing, dust mitigation, and operations must account for a time-variable and state-dependent environment.
At the same time, electrical behaviour becomes a measurable property of the surface that may provide a new way to probe exposure history without sample return. Differences in relaxation timescale across geological settings offer a testable framework for linking surface physics to regolith evolution.
This is not a complete model. The mechanisms at the grain scale, the role of plasma sheath structure, and the contribution of local composition remain to be resolved. What is established is more limited and more important: the assumption of an instantaneous, memoryless surface is not sufficient. The lunar regolith has a state, and that state matters.
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