Lunar Hydration: Discoveries & Impact, by Pranjal Garg
Updated: 1 hour ago
Water, water everywhere and not a drop to drink?
The prevailing scientific paradigm regarding the Moon underwent a fundamental shift following the Apollo era. Long assumed to be entirely volatile-depleted, the Moon is now known to contain hydroxyl groups, mineral-bound water and substantial deposits of water ice, although liquid water cannot persist on its surface. Pranjal’s fascinating talk outlined the geological context, mission history, origins, and strategic importance of lunar hydration for solar system science and deep-space exploration. All delivered with great enthusiasm and panache!
Geological Context & Early Evolution
High-resolution numerical simulations suggest that the Moon could have formed rapidly following a Mars-sized collision with the proto-Earth, accreting within hours. At this early stage, Earth’s rotation period may have been approximately six hours. It later lengthened to around 18 hours about a billion years ago, during the Proterozoic Eon, and roughly 22–23 hours during the Mesozoic Era (the age of the dinosaurs), before reaching 24 hours today.
Frederik introduces Pranjal to the Flamsteed, and Pranjal during the talk. Pictures by Tony Milon.
The lunar surface displays a stark dichotomy between the ancient, heavily cratered Highlands (composed largely of anorthositic breccia) and the younger Maria (basaltic plains formed via intense volcanic flooding). Although global volatile retention remained low due to the lack of an atmosphere and low gravity, extreme thermal conditions in polar regions created stable reservoirs. These Permanently Shadowed Regions (PSRs) located in deep polar craters never receive direct sunlight and maintain temperatures low enough to preserve water ice over billions of years.
Chronology of Discovery
The understanding of lunar water evolved across six decades of theoretical modelling, lunar sample analysis, and orbital and impactor missions.
1961 Theoretical models proposed that volatile species could be trapped in polar cold traps thus establishing the foundation for polar hydration searches.
1969-1972 Apollo 11–17 Returned basalt and breccia samples showed no detectable native water, reinforcing the long-held paradigm of a completely dry Moon.
1994 The Clementine satellite’s radar measurements over the lunar poles provided initial, albeit contested, hints of polar ice.
1998 Lunar Prospector’s spectrometer confirmed high concentrations of hydrogen in shadowed polar craters.
2008 Chandrayaan-1’s Moon Mineralogy Mapper detected infrared absorption bands at 3μm, thus proving widespread surface hydration.
2009 Observations by the Lunar Crater Observation and Sensing Satellite (LCROSS) and Lunar Reconnaissance Orbiter (LRO), following the controlled impact of the Centaur upper stage into Cabeus crater, confirmed the presence of water ice and vapour in the resulting debris plume.
2020 The Stratospheric Observatory for Infrared Astronomy (SOFIA) used infrared spectroscopy at a wavelength of approximately 6μm to detect H₂O in Clavius crater, demonstrating that molecular water exists outside permanently shadowed regions.
More pictures of Pranjal during the talk. Pictures by Paul May and Frederik Botha.
Mechanisms & Sources of Hydration
Lunar hydration stems from two primary pathways: endogenic (internal/magmatic) and exogenic (external/delivery).
Endogenic (Magmatic) sources are primarily from pyroclastic deposits. Analysis of volcanic glass beads reveals water trapped within the lunar interior during ancient explosive eruptions.
Exogenic (External) sources include solar wind implantation and impact delivery. The former involves bombardment of the lunar regolith by high-energy solar wind protons producing hydroxyl groups and hydroxylated minerals. The latter results from impactors such as carbonaceous chondrites and comets which continually deliver hydrated silicates and water ice directly to the lunar surface.
Strategic Impact & Future Exploration
Understanding lunar hydration delivers dual benefits: both unravelling the volatile history of the Earth-Moon system and enabling sustainable deep-space exploration. Preserved volatile ice deposits act as a historical record of volatile delivery to the early Earth-Moon system, offering insights into Earth's oceans and early atmosphere.
Future lunar missions will leverage polar resources to establish a permanent human presence. Water extracted from polar ice reserves provides essential drinking water and oxygen via electrolysis for crewed habitats. In addition, electrolysis splits lunar water into oxygen and hydrogen, which can then be liquefied for use as rocket propellants, enabling local refuelling of landers and spacecraft. Utilizing lunar propellant significantly reduces launch mass requirements from Earth, positioning the Moon as a gateway and testbed for crewed missions to Mars.
So, water may not be everywhere, but it is certainly present as ice in permanently shadowed polar craters and elsewhere on the Moon within volcanic and impact-formed glass beads. And potentially plenty of drops to drink, once that ice has been extracted, melted and purified!
A recording of this excellent and fascinating talk is available to members.
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