Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany.
Nature. 2011 Oct 5;478(7368):218-20. doi: 10.1038/nature10519.
For decades, the source of Earth's volatiles, especially water with a deuterium-to-hydrogen ratio (D/H) of (1.558 ± 0.001) × 10(-4), has been a subject of debate. The similarity of Earth's bulk composition to that of meteorites known as enstatite chondrites suggests a dry proto-Earth with subsequent delivery of volatiles by local accretion or impacts of asteroids or comets. Previous measurements in six comets from the Oort cloud yielded a mean D/H ratio of (2.96 ± 0.25) × 10(-4). The D/H value in carbonaceous chondrites, (1.4 ± 0.1) × 10(-4), together with dynamical simulations, led to models in which asteroids were the main source of Earth's water, with ≤10 per cent being delivered by comets. Here we report that the D/H ratio in the Jupiter-family comet 103P/Hartley 2, which originated in the Kuiper belt, is (1.61 ± 0.24) × 10(-4). This result substantially expands the reservoir of Earth ocean-like water to include some comets, and is consistent with the emerging picture of a complex dynamical evolution of the early Solar System.
几十年来，地球挥发物的来源，特别是氘氢比（D/H）为（1.558±0.001）×10(-4)的水的来源，一直是一个争论的话题。地球的总体成分与被称为顽火辉石球粒陨石的陨石相似，这表明原始地球是干燥的，随后通过局部吸积或小行星或彗星的撞击输送挥发物。先前对来自奥尔特云的六颗彗星的测量结果得出的 D/H 比值平均值为（2.96±0.25）×10(-4)。碳质球粒陨石的 D/H 值为（1.4±0.1）×10(-4)，再加上动力学模拟，导致了这样的模型，即小行星是地球水的主要来源，只有≤10%的水是由彗星输送的。在这里，我们报告说，起源于柯伊伯带的木星族彗星 103P/Hartley 2 的 D/H 比值为（1.61±0.24）×10(-4)。这一结果大大扩展了地球海洋样水的储层，包括一些彗星，并与早期太阳系复杂动力学演化的新图景相一致。
