The extent of volatile elements on the surface and interior of the Moon remains a highly debated topic. Previous studies conducted on bulk lunar soil samples and solar wind samples collected by the Genesis mission indicate a discernible isotope mass- or non-mass-dependent fractionation of krypton and xenon. However, a detailed investigation of these processes is missing, particularly in determining the possible incorporation of cometary volatiles in the lunar regolith. New lunar soil samples returned by the Chang'e-5 mission provide a chance to answer these key questions. In this study, noble gas isotopes of nine subsamples from a Chang'e-5 scooped sample were analysed through stepwise-heating and total fusion laser extraction. The results reveal that a simple binary mixture of solar wind and cosmogenic components did not explain alone the isotopic composition of these samples. The Xe data shows insignificant amounts of atmospheric Xe and presents clear evidence of cometary contributions to the lunar regolith, with a significant depletion of 134,136Xe compared to that in the solar wind. Additionally, a meteoritic component is identified. Compared to the Apollo results, our findings further validate the theory of Earth's atmospheric escape, substantiate the plausibility of these exogenous admixtures to elucidate the isotopic fractionation mechanisms of Kr and Xe within the lunar regolith, and provide novel insights into long-term constancy in the solar wind composition.

Despite extensive effort during the last four decades, no clear signature of a lunar indigenous noble gas component has been found. In order to further investigate the possible occurrence of indigenous volatiles in the Moon, we have re-analyzed the noble gas and nitrogen isotopic compositions in three anorthosite samples. Lunar anorthosites 60025, 60215 and 65315 have the lowest exposure duration (similar to 2 Ma) among Apollo samples and consequently contain only limited cosmogenic (e.g. Xe-124,Xe-126) and solar wind (SW) noble gases. Furthermore, anorthosites have negligible contributions of fissiogenic Xe isotopes because of their very low Pu and U contents. As observed in previous studies (Lightner and Marti, 1974; Leich and Niemeyer, 1975), lunar anorthosite Xe presents an isotopic composition very close to that of terrestrial atmospheric Xe, previously attributed to anomalous adsorption of terrestrial Xe after sample return. The presumed atmospheric Xe contamination can only be removed by heating the samples at medium to high temperatures under vacuum, and is therefore different from common adsorption. To test this hypothesis, we monitored the adsorption of Xe onto lunar anorthositic powder using infrared reflectance spectroscopy. A clear shift in the anorthosite IR absorbance peaks is detected when comparing the IR absorbance spectra of the lunar anorthositic powder before and after exposure to a neutral Xe-rich atmosphere. This observation accounts for the chemical bonding (chemisorption) of Xe onto anorthosite, which is stronger than the common physical bonding (physisorption) and could account for the anomalous adsorption of Xe onto lunar samples. Our high precision Xe isotope analyses show slight mass fractionation patterns across Xe128-136 isotopes with systematic deficits in the heavy Xe isotopes (mostly Xe-136 and marginally Xe-134) that have not previously been observed. This composition could be the result of mixing between an irreversibly adsorbed terrestrial contaminant that is mostly released at high temperature and an additional signature. Solar Wind (SW) Xe contents, estimated from SW-Ne and SW-Ar concentrations and SW-Ne/Ar/Xe elemental ratios, do not support SW as the additional contribution. Using a chi(2) test, the latter is best accounted for by cometary Xe as measured in the coma of Comet 67P/Churyumov-Gerasimenko (Marty et al., 2017) or by the primordial U-Xe composition inferred to be the precursor of atmospheric Xe (Pepin, 1994; Avice et al., 2017). It could have been contributed to the lunar budget by volatile-rich bodies that participated to the building of the terrestrial atmosphere inventory (Marty et al., 2017). (C) 2017 The Author(s). Published by Elsevier Ltd.

The Neutral Mass Spectrometer (NMS) of the Lunar Atmosphere and Dust Environment Explorer (LADEE) Mission is designed to measure the composition and variability of the tenuous lunar atmosphere. The NMS complements two other instruments on the LADEE spacecraft designed to secure spectroscopic measurements of lunar composition and in situ measurement of lunar dust over the course of a 100-day mission in order to sample multiple lunation periods. The NMS utilizes a dual ion source designed to measure both surface reactive and inert species and a quadrupole analyzer. The NMS is expected to secure time resolved measurements of helium and argon and determine abundance or upper limits for many other species either sputtered or thermally evolved from the lunar surface.