regolith

Regolith is the layer of loose, heterogeneous material that covers solid rock on a planetary body, moon, or asteroid. It encompasses dust, broken rock, volcanic ash, and other weathered debris, as well as material produced by impacts or thermal cycling. Regolith forms through weathering, erosion, and, in airless or near-airless environments, micrometeorite bombardment that pulverizes bedrock. It may also include chemically altered components depending on the local environment.

On Earth, regolith is often referred to as the surface layer of soil and unconsolidated material overlaying bedrock. Its thickness varies from a few centimeters to many meters and reflects local geology and climate. The composition can include organic matter, clay, silt, sand, gravel, and weathered rock fragments. Regolith supports vegetation and is integral to processes such as nutrient cycling and water infiltration, though its properties differ from those of true bedrock and of consolidated soils.

In the Moon, regolith results mainly from micrometeorite impacts and solar wind interactions, producing a fine, abrasive dust and glassy agglutinates. It lacks an atmosphere and active weathering, so the regolith has a distinctive, coarse-to-fine texture with variability in depth across the surface. Apollo samples and remote sensing studies have revealed its glassy components and subsurface layering.

Regolith also covers Mars and many asteroids. Martian regolith ranges from fine dust to coarse grains and contains minerals derived from volcanic and impact processes, including perchlorates and iron oxides. On asteroids, regolith is typically a loose, unconsolidated layer formed by constant bombardment in low gravity, influencing landing, sampling, and in situ resource utilization strategies.