近日，美国加州理工学院Amy E. Hofmann团队报道了氧同位素证据表明，火星盖尔陨石坑是早期西方水库的所在地，该水库经历了大量蒸发。该研究于2025年10月20日发表在《美国科学院院刊》杂志上。
“好奇号”火星车在盖尔陨石坑的含粘土单元内采集了粉状岩石样品，在热解过程中对水中的HDO、H218O和H216O进行了同时测量，结果表明，这些样品的重同位素富集程度极端多变，平均为陆地海水D/H比的~4.5倍和18O/16O比的~1.03倍。这些富集物记录在从矿物表面解吸的水中，并从低结晶相、水合盐、黄钾铁矾和粘土中演化而来。所有进化出的水相对于普通的陆地水都是富氘的，这反映了氢在太空中的损失。
由于结构上结合的羟基上的氧在地质时间尺度上与其他氧交换的可能性最小，因此研究组将重点放在蒙脱石粘土脱羟基过程中水中演化的氧上。一些样品的18O/16O比例与降水相当，或者与相对于地球大气水的18O含量适度丰富的水接近完全平衡，这与火星水圈在氧同位素方面基本与地球水圈相似的其他证据一致。与氢气不同的是，大气中氧气的逸出并没有导致火星上氧的极端富集。
然而，在局部地区，大多数盖尔密脱岩的18O/16O值需要母体水中明显的18O富集。在地球上，地表水中最极端的18O富集是在封闭的盆地中发现的，这些盆地经历了大量的蒸发损失，进入了低湿度的大气中，在这些环境中形成的自生粘土矿物的18O/16O反映了这些富集。在粘土形成和早期成岩作用时期，盖尔当地的水文储层也发生了类似的作用，这是这些粘土独特的氧同位素组成的一个合理解释。
附：英文原文
Title: Oxygen isotopic evidence that Gale crater, Mars, was home to an Early Hesperian water reservoir that underwent significant evaporation
Author: Hofmann, Amy E., Archer, P. Douglas, McAdam, Amy C., Sutter, Brad, Bristow, Thomas F., Eiler, John M., Webster, Christopher R., Flesch, Gregory J., Fraeman, Abigail A., Franz, Heather B., House, Christopher H., Rampe, Elizabeth B., Stern, Jennifer C., Mahaffy, Paul R., Malespin, Charles A., Grotzinger, John P., Vasavada, Ashwin R.
Issue&Volume: 2025-10-20
Abstract: Simultaneous measurements of HDO, H218O, and H216O in water evolved during pyrolysis of powdered rock samples acquired by the Curiosity rover within Gale crater’s clay-bearing units indicate extreme and variable heavy-isotope enrichments averaging ~4.5 times the D/H ratio and ~1.03 times the 18O/16O ratio of terrestrial seawater. These enrichments are recorded in water desorbed from mineral surfaces and evolved from poorly crystalline phases, hydrated salts, jarosite, and clays. All evolved waters are deuterium-enriched relative to common terrestrial waters, reflecting hydrogen loss to space. Because oxygen in structurally bound hydroxyl groups is least likely to exchange with other sources over geologic timescales, we focus on oxygen in water evolved during dehydroxylation of smectite clays. Several samples have 18O/16O ratios commensurate with precipitation from, or near-complete equilibration with, water moderately 18O-enriched relative to terrestrial meteoric waters—consistent with other evidence that Mars’s hydrosphere is basically like Earth’s in terms of oxygen isotopes. Unlike hydrogen, oxygen atmospheric escape did not lead to extreme 18O enrichments on Mars. Locally, however, most Gale smectites’ 18O/16O values require a pronounced 18O-enrichment of their parental waters. On Earth, the most extreme 18O enrichments in surface waters are found in closed basins having undergone significant evaporative loss into a low-humidity atmosphere, and the 18O/16O of authigenic clay minerals formed in these environs reflect those enrichments. A similar process acting on the hydrologic reservoir local to Gale at the time of clay formation and early diagenesis is a plausible explanation for the distinctive oxygen isotopic compositions of these clays.
DOI: 10.1073/pnas.2511627122
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2511627122