The presence and distribution of water on the Moon are fundamental to our understanding of the Earth–Moon system. Despite extensive laboratory research and remote sensing explorations, the origin and chemical form of lunar water have remained elusive. In this study we present the discovery of a hydrated mineral, (NH₄)MgCl₃·6H₂O, in lunar soil samples returned by the Chang’e-5 mission that contains approximately 41 wt% H₂O. The mineral’s structure and composition closely resemble novograblenovite, a terrestrial fumarole mineral formed through the reaction of hot basalt with water-rich volcanic gases, and carnallite, an Earth evaporite mineral. We rule out terrestrial contamination or rocket exhaust as the origin of this hydrate on the basis of its chemical and isotopic compositions and formation conditions. The presence of ammonium indicates a more complex lunar degassing history and highlights its potential as a resource for lunar habitation. Our findings also suggest that water molecules can persist in sunlit areas of the Moon as hydrated salts, providing crucial constraints on the fugacity of water and ammonia vapour in lunar volcanic gases.

月球上水的存在和分布是我们了解地月系统的基础。尽管进行了大量的实验室研究和遥感探索，但月球水的起源和化学形式仍然难以捉摸。在这项研究中，我们在长'号返回的月球土壤样本中发现了一种水合矿物，(NH ₄ )MgCl ₃ ·6H ₂ O。 e-5 任务包含约 41 wt% H ₂ O。该矿物的结构和成分与新格拉布尔诺维特（一种通过热玄武岩与富含水的火山气体和光卤石反应形成的陆地喷气孔矿物）非常相似，一种地球蒸发岩矿物。根据其化学和同位素组成以及形成条件，我们排除了陆地污染或火箭尾气作为这种水合物的来源。铵的存在表明月球脱气历史更加复杂，并凸显了其作为月球居住资源的潜力。我们的研究结果还表明，水分子可以以水合盐的形式存在于月球的阳光照射区域，这对月球火山气体中水和氨蒸气的逸度提供了关键的限制。