Esat T M, Brownlee D E, Papanastassiou D A, Wasserburg G J
Science. 1979 Oct 12;206(4415):190-7. doi: 10.1126/science.206.4415.190.
The magnesium isotopic composition of some extraterrestrial dust particles has been measured. The particles are believed to be samples of interplanetary dust, a significant fraction of which originated from the disaggregation of comets and may contain preserved isotopic anomalies. Improvements in mass spectrometric and sample preparation techniques have made it possible to measure the magnesium isotopic composition of the dust particles, which are typically 10 micrometers in size and contain on the order of 10(-10) gram of magnesium. Of the 13 samples analyzed, nine have the terrestrial magnesium isotopic composition within 2 parts per thousand, and one shows isotopic mass fractionation of 1.1 percent per mass unit. A subset of the particles, described as chondritic aggregates, are very close to normal isotopic composition, but their normalized isotopic ratios appear to show nonlinear effects of 3 to 4 parts per thousand, which is near the present limit of detection for samples of this size. The isotopic composition of calcium was also determined in one particle and found to be normal within 2 percent. It is clear that the isotopic composition of interplanetary dust particles can be determined with good precision. Collection of dust particles during the earth's passage through a comet tail or an intense meteor stream may permit laboratory analysis of material from a known comet.
已对一些地外尘埃颗粒的镁同位素组成进行了测量。这些颗粒被认为是行星际尘埃的样本，其中很大一部分源自彗星的解体，可能含有保存下来的同位素异常。质谱分析和样品制备技术的改进使得测量尘埃颗粒的镁同位素组成成为可能，这些尘埃颗粒通常大小为10微米，含有约10(-10)克的镁。在分析的13个样本中，9个样本的地球镁同位素组成在千分之二以内，1个样本显示出每质量单位1.1%的同位素质量分馏。一部分被描述为球粒状聚集体的颗粒非常接近正常同位素组成，但其归一化同位素比率似乎显示出千分之三到四的非线性效应，这接近这种大小样本目前的检测极限。还对一个颗粒中的钙同位素组成进行了测定，发现其在2%以内是正常的。显然，可以高精度地测定行星际尘埃颗粒的同位素组成。在地球穿过彗尾或强烈流星流期间收集尘埃颗粒，可能会使实验室能够分析来自已知彗星的物质。
