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#1
American geologist George P. Merrill coined the scientific term regolith in 1897 by combining the Greek words rhegos (meaning blanket) and lithos (meaning rock).
#2
Unlike terrestrial soil, lunar regolith contains zero organic matter, zero biological humus, and no free liquid water, making the geological term regolith scientifically distinct from organic soil.
#3
Lunar regolith thickness averages 4 to 5 meters in the younger basaltic maria and 10 to 15 meters across the ancient, heavily cratered feldspathic highlands.
#4
Directly beneath the fine surface regolith lies the megaregolith, a fractured zone of large ejecta blocks and shattered crustal rock extending several kilometers into the lunar crust.
#5
Hypervelocity micrometeoroids striking the airless lunar surface at velocities between 10 and 70 kilometers per second comminute larger rocks and melt surface silicates.
#6
Agglutinates are irregular, glass-bonded mineral aggregates formed when micrometeoroid impact melts fuse surrounding dust grains; they constitute 25% to 60% of mature lunar regolith.
#7
Space weathering reduces ferrous iron (FeO) in silicate minerals into microscopic droplets of pure metallic nanophase iron (npFe0), which darkens the surface albedo and reddens reflectance spectra.
#8
Because lunar dust grains never undergo wind or water erosion, they retain razor-sharp, vesicular edges that abrade spacesuit fabrics, mechanical bearings, and vacuum pressure seals.
#9
Ultraviolet solar radiation and solar wind plasma impart an electrostatic charge to lunar dust particles, causing them to levitate above the terminator boundary and cling stubbornly to visor surfaces.
#10
In August 2023, Chandrayaan-3 payloads LIBS and APXS detected sulfur, aluminum, calcium, iron, chromium, titanium, manganese, silicon, and oxygen in the southern high-latitude regolith at 69.37 degrees South.
#11
Lunar mare regolith is enriched in basaltic minerals such as pyroxene, olivine, and ilmenite (FeTiO3), whereas highland regolith is dominated by calcium-rich plagioclase feldspar (anorthosite).
#12
Solar wind bombardment over billions of years implants volatile gases directly into lunar regolith grains, including hydrogen, helium-3 (3He), neon, carbon, and nitrogen.
#13
Helium-3, a non-radioactive isotope scarce on Earth, is trapped in higher concentrations within titanium-rich ilmenite grains of lunar mare regolith and is researched as a candidate fuel for aneutronic nuclear fusion.
#14
Martian regolith covers the surface of Mars with iron-oxide-rich dust (hematite and nanophase ferric oxides) and contains between 0.5% and 1% toxic perchlorate salts (ClO4-) detected by NASA’s Phoenix lander in 2008.
#15
On carbonaceous asteroids such as 101955 Bennu (sampled by OSIRIS-REx) and 162173 Ryugu (sampled by Hayabusa2), thermal fatigue from rapid day-night temperature swings fractures boulders into coarse cobble regolith.
#16
Lunar regolith exhibits an extremely low thermal conductivity in vacuum—roughly ten times more insulating than dry beach sand—causing diurnal temperatures to swing from +120 degrees Celsius at noon to -130 degrees Celsius at night within the top 2 centimeters.
#17
Below a depth of approximately 50 to 80 centimeters, lunar regolith acts as a thermal insulator, maintaining a nearly constant subsurface temperature of around -30 to -35 degrees Celsius near the equator.
#18
In permanently shadowed regions (PSRs) near the lunar south pole, regolith temperatures drop below -160 degrees Celsius, allowing water ice crystals mixed within the pore spaces of the regolith to remain stable for billions of years.
#19
In-Situ Resource Utilization (ISRU) experiments extract molecular oxygen from lunar regolith by heating ilmenite (FeTiO3) with hydrogen gas at 900 degrees Celsius to yield metallic iron and water vapor, which is then electrolyzed.
#20
Highland lunar regolith simulants such as LSS-ISRO-1 (developed using terrestrial anorthosite from Sithampoondi and Kunnamalai in Tamil Nadu, India) are engineered to test rover mobility and landing thrusters before flight.
Subject Specialist Commentary
Analytical perspective & practical exam advice from the Master10 academic board
Planetary regolith is a high-frequency topic across UPSC Civil Services, CDS, and CAPF science sections because it bridges geology, space physics, and India's lunar exploration roadmap. Aspirants must distinguish clearly between terrestrial soil—which requires biological decomposition and hydrological weathering—and planetary regolith, which is driven entirely by mechanical impact comminution and space weathering. Special attention should be given to the geochemical distinction between titanium-rich basaltic mare regolith and aluminum-and-calcium-rich anorthositic highland regolith sampled by Chandrayaan-3 at Shiv Shakti Point.
In analytical and Mains questions, examiners link lunar regolith directly to In-Situ Resource Utilization (ISRU) and sustainable lunar base engineering. Specifically, candidates should note how Tamil Nadu's Sithampoondi anorthosite complex provided the exact mineralogical match for ISRO's lunar highland regolith simulant, and how extracting oxygen from ilmenite and water ice from polar regolith determines the economic viability of deep-space missions.
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