Understanding the origin and evolution of water in the Moon through lunar sample studies

Abstract

A paradigm shift has recently occurred in our knowledge and understanding of water in the lunar interior. This has transpired principally through continued analysis of returned lunar samples using modern analytical instrumentation. While these recent studies have undoubtedly measured indigenous water in lunar samples they have also highlighted our current limitations and some future challenges that need to be overcome in order to fully understand the origin, distribution and evolution of water in the lunar interior. Another exciting recent development in the field of lunar science has been the unambiguous detection of water or water ice on the surface of the Moon through instruments flown on a number of orbiting spacecraft missions. Considered together, sample-based studies and those from orbit strongly suggest that the Moon is not an anhydrous planetary body, as previously believed. New observations and measurements support the possibility of a wet lunar interior and the presence of distinct reservoirs of water on the lunar surface. Furthermore, an approach combining measurements of water abundance in lunar samples and its hydrogen isotopic composition has proved to be of vital importance to fingerprint and elucidate processes and source(s) involved in giving rise to the lunar water inventory. A number of sources are likely to have contributed to the water inventory of the Moon ranging from primordial water to meteorite-derived water ice through to the water formed during the reaction of solar wind hydrogen with the lunar soil. Perhaps two of the most striking findings from these recent studies are the revelation that at least some portions of the lunar interior are as water-rich as some Mid-Ocean Ridge Basalt source regions on Earth and that the water in the Earth and the Moon probably share a common origin.

Water in the Moon's interior: Truth and consequences

“…Measurement of water in lunar apatite, at levels similar to terrestrial apatite, has added weight to this discovery (Boyce et al, 2010(Boyce et al, , 2014McCubbin et al, 2010;Greenwood et al, 2011;Anand et al, 2014;Barnes et al, 2013Barnes et al, , 2014Tartèse et al, , 2014. These surprising results, the culmination of over four decades of intensive geochemical dowsing, provide a severe connature of the Moon compared with the Earth (Krähenbühl et al, 1973a(Krähenbühl et al, , 1973bTera and Wasserburg, 1976;Ringwood and Kesson, 1977;McDonough et al, 1992).…”

“…Rather, they are the most primitive magmas produced by melting and melt migration processes in the lunar Neal (2008). Thick colored lines are liquid lines of descent, calculated using AlphaMelts (Antoshechkina et al, 2010;Asimow and Ghiorso, 1998;Ghiorso and Sack, 1995;Smith and Asimow, 2005) for fractional crystallization of several lunar volcanic glass compositions; low-Ti green glasses (green lines), medium-Ti yellow glasses (yellow lines), and high-Ti red glasses (red lines). Solid LLDs represent crystallization of olivine + pyroxene + oxide where the oxide phase varies continuously from Cr-AlMg spinel at high MgO to Fe-Ti oxide at low MgO.…”

Lunar surface mineralogy using hyperspectral data: Implications for primordial crust in the Earth–Moon system

“…The presence of water molecules in Lunar magma was investigated through in-situ analysis and the results show that the Lunar Magma Ocean (LMO) which contributed to the formation of primordial crust was Hydrous. The water molecules were trapped within olivine crystals before eruption and there was no degassing after eruption (e.g., Hauri et al, 2011;Anand et al, 2014). The composition is broadly similar to primitive terrestrial mid-ocean ridge basalts and show that water molecules present in the parts of Lunar interior is comparable with Earth's upper mantle (e.g., Hauri et al, 2011).…”

The Moon as a Recorder of Organic Evolution in the Early Solar System: A Lunar Regolith Analog Study

“…This also extends to space environments: the parent asteroidal bodies from which type 1 and 2 carbonaceous chondrites originated have experienced varying levels of aqueous alteration that has affected the composition and structure of the organic material (e.g., Sephton et al, 2004b). The Moon is essentially an anhydrous environment, although local sources of hydration may be provided by the hydrated silicate minerals of meteorites (Court and Sephton, 2014), hydrated volcanic pyroclastic glass beads (Saal et al, 2008(Saal et al, , 2013Hauri et al, 2011), indigenous minerals like apatite, and implanted solar wind (Pieters et al, 2009; for reviews see Anand et al, 2014, andRobinson and.…”