Lunar regolith

Regolith is unconsolidated material lying over solid bedrock. On the Moon it ranges from boulders and rock fragments to very fine dust. The word “soil” is often used informally for lunar surface material, but lunar soil is not equivalent to Earth soil: it lacks organic matter and does not form through biological activity. NASA planetary scientist Sarah Noble describes common lunar-regolith components as rock chips, mineral fragments, impact and volcanic glass, and agglutinates—composite grains in which mineral fragments are fused together by glass. Their proportions vary from sample to sample.

The Moon has no dense atmosphere to shield its surface from small impactors. Over long periods, meteoroid impacts fracture rocks, produce melt and eject material that falls back onto the surface. Repeated impacts break grains down while also fusing some material into glass-rich aggregates. Solar-wind particles and cosmic radiation modify exposed grain surfaces. These processes, collectively referred to as space weathering, give lunar samples features that record prolonged exposure to the space environment.

Lunar grains are often angular and have fresh fractured surfaces because the Moon lacks the wind and liquid-water processes that commonly round and sort particles on Earth. The material spans a wide range of sizes, including a very fine dust fraction. Its properties depend on location and exposure history. The 2007 review by Colwell and colleagues explains that lunar regolith is mechanically complex and that fine particles can interact with the electrically charged environment near the airless surface. Dust may be mobilized by impacts, electrostatic forces, or human and mechanical activity; its behavior remains an active subject of research.

Regolith is the surface material on which landers, rovers, and crews must operate. Fine, abrasive material can affect equipment and spacesuits, while its mechanical behavior matters for landing, mobility, excavation, and construction. NASA identifies these hazards as important considerations for longer stays on the Moon. At the same time, regolith is a locally available resource under investigation for potential uses such as construction materials, extracting useful substances, and supporting plant-growth research. Such applications remain areas of research rather than established lunar infrastructure.

Because regolith accumulates products of impacts and space exposure, samples help researchers investigate lunar geology and the history of surface processes. Differences in grains and glassy components provide clues about source rocks and alteration. Dust transport also connects surface-material studies to questions about the lunar plasma environment and phenomena such as horizon glow. A 2024 review of lunar dust emphasizes that important mechanisms and properties are still incompletely understood, especially for predicting transport under different lunar conditions.