What does regolith mean?
Regolith is the loose material that forms a covering above a planet's solid surface or bedrock. It may consist of soil, dust, gravel, volcanic ash, and fragments created by weathering, erosion, or impacts. On Earth, regolith can extend from the soil surface to the transition with unaltered rock; on the Moon and Mars, it forms a substantial surface layer of finely pulverized material. The term is especially important in planetary science because it records a body's history and affects spacecraft landing, rover movement, and the possibility of preserving traces of past activity. Regolith is broader than soil: soil usually emphasizes the biologically active, organic-rich portion of the surface, while regolith is a geological term covering all the loose material above bedrock.
nounRegolith is a layer of loose, fragmented material, such as soil, dust, gravel, or broken rock, that covers a planet's surface or lies above solid bedrock. On Earth, it forms through weathering and erosion; on the Moon and Mars, it includes impact-generated dust and debris.
- The layer of loose, fragmented material covering a planet's surface or overlying solid bedrock.
- In terrestrial geology, the zone of weathered and broken rock above unaltered bedrock.
"The lunar module left footprints in the fine regolith near the descent stage."
"Scientists analyzed samples of Martian regolith to investigate the planet's past environment."
"The cliff exposes a thick band of regolith beneath a layer of solid sandstone."
The plural is used when referring to regolith from different planets, bodies, or locations.
"The lunar and Martian regoliths have different compositions and physical properties."
Every footprint left by an Apollo astronaut on the Moon is a small monument in regolith, the ancient dust that has barely changed since its formation.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does regolith come from?
The word was coined in the early 20th century from Greek rhēgos, meaning “rubble” or “broken stone,” and lithos, meaning “stone.” Its formation follows the usual English pattern of joining two Greek roots into a technical geological term. The same roots also appear in words such as rheology and lithology, although their meanings developed independently.
Related word forms
How regolith is actually used
Regolith is primarily a technical term in geology and planetary science. In discussions of the Moon or other airless bodies, it often denotes unconsolidated dust and rock fragments produced largely by impacts; in terrestrial geology, its composition can include soil, weathered fragments, and volcanic material.
Easily confused with regolith
Regolith is the broader geological layer of loose material above bedrock, whereas soil specifically refers to the biologically active upper portion containing organic matter and organisms.