NASA平流层尘埃12粒样本：海王星外柯伊伯带古水库氧18富集15%
美国国家航空航天局（NASA）约翰逊航天中心 Lindsay Keller 领衔、加州大学洛杉矶分校合作团队在《Science Advances》2026年发表研究，分析从地球平流层收集的微小行星际尘埃颗粒，识别出12粒带有古代水与岩石相互作用证据的颗粒。
研究人员测量颗粒内氧同位素比值后推断，早期外太阳系的水显著富集重氧氧17和氧18。计算显示氧18较地球标准富集15%，构成可区分不同太阳系储库的化学指纹。电子显微分析显示颗粒主要由含水黏土矿物皂石以及富镁、富铁碳酸盐组成。
这些颗粒内太阳辐射留下的径迹密度高，研究团队据此推断其在太空中的旅行时间超过100万年，来源远于典型小行星带。研究团队表示，下一步将分析更多颗粒，判断这一同位素特征是柯伊伯带的普遍特征还是只属于特定母体，并与小行星 Bennu 等样本作比较。
NASA Stratosphere Dust: 12 Grains Point to Ancient Water Reservoir Beyond Neptune in Kuiper Belt
A team led by Lindsay Keller of NASA's Johnson Space Center, with collaborators at the University of California, Los Angeles, reported in Science Advances in 2026 on microscopic interplanetary dust particles collected from Earth's stratosphere, identifying 12 grains that contain evidence of ancient water-rock interactions.
Measuring oxygen isotope ratios in the grains, the scientists inferred that water in the early outer solar system was significantly enriched in heavy oxygen, oxygen-17 and oxygen-18, compared with water in Earth's oceans. The calculated enrichment in oxygen-18 was 15% compared with Earth's standard, providing a chemical fingerprint that may help distinguish materials from different solar system reservoirs. Electron microscopy showed the grains are primarily composed of saponite, a water-bearing clay mineral, alongside magnesium- and iron-rich carbonates.
High densities of solar-radiation tracks in the grains indicate travel times exceeding a million years, suggesting an origin much farther out than the typical asteroid belt, the team said. Future work will analyse additional grains to determine whether the isotopic signature is widespread in the Kuiper Belt or specific to particular parent bodies, and will compare the results with samples from asteroids such as Bennu.
来源：美国国家航空航天局约翰逊航天中心
发布：GSM·美国（发布链接）
图片来源：图中是一粒多孔球粒陨石质行星际尘埃颗粒，与本研究分析的平流层尘埃颗粒同类。来源：Wikimedia Commons, File:Porous chondriteIDP.jpg, The original uploader was Amara at English Wikipedia, CC BY 1.0。
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