Recent fluid flow in ancient meteorites Carbonaceous chondritic meteorites are thought to be fragments broken off parent bodies that orbit in the outer Solar System, largely unaltered since their formation. These meteorites contain evidence of reactions with liquid water that was thought to have been lost or completely frozen billions of years ago. Turner et al. examined uranium and thorium isotopes in several carbonaceous chondrites, finding nonequilibrium distributions that imply that uranium ions were transported by fluid flow. Because this signature disappears after several half-lives of the radioactive isotopes, the meteorites must have been exposed to liquid within the past million years. The authors suggest that ice may have melted during the impacts that ejected the meteorites from their parent bodies. Science, this issue p. 164 Uranium-series isotopes indicate that carbonaceous chondrite meteorites experienced liquid flow within the past million years. Carbonaceous chondritic meteorites are primordial Solar System materials and a source of water delivery to Earth. Fluid flow on the parent bodies of these meteorites is known to have occurred very early in Solar System history (first <4 million years). We analyze short-lived uranium isotopes in carbonaceous chondrites, finding excesses of 234-uranium over 238-uranium and 238-uranium over 230-thorium. These indicate that the fluid-mobile uranium ion U6+ moved within the past few 100,000 years. In some meteorites, this time scale is less than the cosmic-ray exposure age, which measures when they were ejected from their parent body into space. Fluid flow occurred after melting of ice, potentially by impact heating, solar heating, or atmospheric ablation. We favor the impact heating hypothesis, which implies that the parent bodies still contain ice.

中文翻译：

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碳质球粒陨石在过去的百万年中经历了流体流动

古代陨石中的最新流体流动 碳质球粒陨石被认为是从外太阳系中的母体上脱落下来的碎片，自它们形成以来基本上没有改变。这些陨石包含与液态水发生反应的证据，这些水被认为在数十亿年前已经消失或完全冻结。特纳等人。研究了几种碳质球粒陨石中的铀和钍同位素，发现了非平衡分布，表明铀离子是通过流体流动传输的。因为这种特征在放射性同位素的几个半衰期后消失，所以陨石一定在过去的百万年里暴露在液体中。作者认为，在将陨石从其母体中喷射出来的撞击过程中，冰可能已经融化。科学，这个问题 p。164 铀系列同位素表明碳质球粒陨石在过去的百万年中经历了液体流动。碳质球粒陨石是原始太阳系材料，也是向地球输送水的来源。已知这些陨石母体上的流体流动发生在太阳系历史的早期（最初 <400 万年）。我们分析了碳质球粒陨石中的短寿命铀同位素，发现 234-铀超过 238-铀和 238-铀超过 230-钍。这些表明流体移动的铀离子 U6+ 在过去的 100,000 年内移动。在一些陨石中，这个时间尺度小于宇宙射线暴露年龄，宇宙射线暴露年龄是测量它们从母体喷射到太空的时间。冰融化后发生流体流动，可能是由于撞击加热，太阳能加热，或大气烧蚀。我们赞成撞击加热假说，这意味着母体仍然含有冰。