Thiemens Maxwell M, Martinez Morgan H Nunn, Thiemens Mark H
Department of Earth Sciences, University of Edinburgh, Edinburgh EH9 3JW, Scotland, United Kingdom.
Archaeology, Environmental changes & Geo-Chemistry, Vrije Universiteit Brussel, Brussels 1050, Belgium.
Proc Natl Acad Sci U S A. 2024 Dec 24;121(52):e2321069121. doi: 10.1073/pnas.2321069121. Epub 2024 Dec 16.
The origin of water in the Earth-Moon system is a pivotal question in planetary science, particularly with the need for water resources in the race to establish lunar bases. The candidate origins of lunar water are an indigenous lunar component, solar wind water production, and the delivery of meteoritic and cometary material. Characterizing the oxygen isotopic composition of water provides information on lunar oxygen sources. The scarcity of lunar water required the development of a high-precision analytical technique for small samples. This method employs stepwise heating, fluorination, and oxygen isotopic measurements using a dual inlet isotope ratio mass spectrometer. The three heating steps were selected based on other extraterrestrial material studies to release loosely bound water that may have been terrestrially contaminated (50 °C), loosely bound water (150 °C), and tightly bound water (as OH) (1,000 °C). This method was applied to a suite of 9 Apollo samples (basalts, breccias, and a regolith), along with terrestrial and meteoritic controls. We present here measurements of the triple oxygen isotopic composition of this water. Our data predominantly show high Δ'O values (≥ 0‰) for lunar water. These values are consistent with enstatite, ordinary, and CI chondrite-like signatures, although coupling Δ'O with δO forms mixing trends that dominantly overlap enstatite signatures. The other end of the mixing line is in the positive Δ'O space with cometary δO values, providing constraints for cometary Δ'O between 0.75 to 1.75‰.
地月系统中水的起源是行星科学中的一个关键问题，尤其是在建立月球基地的竞争中对水资源有需求的情况下。月球水的候选起源包括月球原生成分、太阳风产水以及陨石和彗星物质的输送。表征水的氧同位素组成可提供有关月球氧源的信息。月球水的稀缺性要求开发一种针对小样本的高精度分析技术。该方法采用逐步加热、氟化以及使用双进样口同位素比率质谱仪进行氧同位素测量。根据其他地外物质研究选择了三个加热步骤，以释放可能已被地球污染的松散结合水（50°C）、松散结合水（150°C）和紧密结合水（以OH形式）（1000°C）。该方法应用于一组9个阿波罗样本（玄武岩、角砾岩和月壤），以及地球和陨石对照样本。我们在此展示了该水中三重氧同位素组成的测量结果。我们的数据主要显示月球水的Δ'O值较高（≥0‰）。这些值与顽火辉石、普通球粒陨石和CI球粒陨石类特征一致，尽管将Δ'O与δO结合形成的混合趋势主要与顽火辉石特征重叠。混合线的另一端位于具有彗星δO值的正Δ'O空间中，为彗星的Δ'O提供了0.75至1.75‰的限制。
