Becker Harry, Walker Richard J
Department of Geology, University of Maryland, College Park, Maryland 20742, USA.
Nature. 2003 Sep 11;425(6954):152-5. doi: 10.1038/nature01975.
The abundances of elements and their isotopes in our Galaxy show wide variations, reflecting different nucleosynthetic processes in stars and the effects of Galactic evolution. These variations contrast with the uniformity of stable isotope abundances for many elements in the Solar System, which implies that processes efficiently homogenized dust and gas from different stellar sources within the young solar nebula. However, isotopic heterogeneity has been recognized on the subcentimetre scale in primitive meteorites, indicating that these preserve a compositional memory of their stellar sources. Small differences in the abundance of stable molybdenum isotopes in bulk rocks of some primitive and differentiated meteorites, relative to terrestrial Mo, suggest large-scale Mo isotopic heterogeneity between some inner Solar System bodies, which implies physical conditions that did not permit efficient mixing of gas and dust. Here we report Mo isotopic data for bulk samples of primitive and differentiated meteorites that show no resolvable deviations from terrestrial Mo. This suggests efficient mixing of gas and dust in the solar nebula at least to 3 au from the Sun, possibly induced by magnetohydrodynamic instabilities. These mixing processes must have occurred before isotopic fractionation of gas-phase elements and volatility-controlled chemical fractionations were established.
我们银河系中元素及其同位素的丰度呈现出广泛的变化，这反映了恒星中不同的核合成过程以及银河系演化的影响。这些变化与太阳系中许多元素稳定同位素丰度的均匀性形成对比，这意味着在年轻的太阳星云内，不同恒星来源的尘埃和气体有效地实现了均匀化。然而，在原始陨石的亚厘米尺度上已经识别出同位素的非均质性，这表明它们保留了其恒星来源的成分记忆。一些原始和分异陨石的块状岩石中，相对于地球钼，稳定钼同位素丰度存在微小差异，这表明太阳系内部一些天体之间存在大规模的钼同位素非均质性，这意味着当时的物理条件不允许气体和尘埃进行有效混合。在此，我们报告了原始和分异陨石块状样品的钼同位素数据，这些数据显示与地球钼没有可分辨的偏差。这表明太阳星云内的气体和尘埃至少在距离太阳3天文单位处实现了有效混合，这可能是由磁流体动力学不稳定性引起的。这些混合过程必定发生在气相元素同位素分馏和挥发性控制的化学分馏形成之前。
