Hydrogen isotope ratios in lunar rocks and the delivery of cometary water to the MoonWater plays a critical role in the evolution of planetary bodies 1 , and determination of the amount and sources of lunar water has profound implications for our understanding of the history of the Earth-Moon system. During the Apollo program, the lunar samples were found to be devoid of indigeneous water 2,3 . The severe depletion of lunar volatiles 4 , including water, has long been seen as strong support for the giant-impact origin of the Moon 5 . Recent studies have found water in lunar volcanic glasses 6 and in lunar apatite 7-9 , but the sources of lunar water have not been determined. Here we report ion microprobe measurements of water and hydrogen isotopes in the hydrous mineral apatite, found in crystalline lunar mare basalts and highlands rocks collected during the Apollo missions. We find significant water in apatite from both mare and highlands rocks, indicating a role for water during all phases of the Moon's magmatic history. Variations of hydrogen isotope ratios in apatite suggest the lunar mantle, solar wind protons, and comets as possible sources for water in lunar rocks and imply a significant delivery of cometary water to the Earth-Moon system shortly after the Moon-forming impact.
Oxygen isotopic composition of our solar system is believed to have resulted from mixing of two isotopically distinct nebular reservoirs, 16 O-rich and 17,18 O-rich relative to Earth. The nature and composition of the 17,18 O-rich reservoir are poorly constrained. We report an in situ discovery of a chemically and isotopically unique material distributed ubiquitously in fine-grained matrix of a primitive carbonaceous chondrite Acfer 094. This material formed by oxidation of Fe,Ni-metal and sulfides by water either in the solar nebula or on a planetesimal. Oxygen isotopic composition of this material indicates that the water was highly enriched in 17 O and 18 O (δ 17,18 O SMOW = +180‰ per mil), providing the first evidence for an extremely 17,18 O-rich reservoir in the early solar system.
Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. Samples of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft. We measure the mineralogy, bulk chemical and isotopic compositions of Ryugu samples. They are mainly composed of materials similar to carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group. The samples consist predominantly of minerals formed in aqueous fluid on a parent planetesimal. The primary minerals were altered by fluids at a temperature of 37 ± 10°C, 5.2 − 0.8 + 0.7 (Stat.) − 2.1 + 1.6 (Syst.) million years after formation of the first solids in the Solar System. After aqueous alteration, the Ryugu samples were likely never heated above ~100°C. The samples have a chemical composition that more closely resembles the Sun’s photosphere than other natural samples do.
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