Nucleosynthetic osmium isotope anomalies in acid leachates of the Murchison meteorite

TL;DR

This study reveals large nucleosynthetic osmium isotope anomalies in the Murchison meteorite, indicating diverse presolar components and providing constraints on stellar nucleosynthesis processes through isotopic analysis.

Contribution

It presents detailed osmium isotopic measurements from the Murchison meteorite, identifying nucleosynthetic anomalies and proposing the existence of distinct presolar phases with different chemical resistances.

Findings

Large internal Os isotope anomalies linked to nucleosynthesis.

Correlation between 190Os and 188Os constrains s-process ratios.

Evidence of diverse presolar grains affecting isotopic compositions.

Abstract

We present osmium isotopic results obtained by sequential leaching of the Murchison meteorite, which reveal the existence of very large internal anomalies of nucleosynthetic origin. The Os isotopic anomalies are correlated, and can be explained by the variable contributions of components derived from the s, r and p-processes of nucleosynthesis. Much of the s-process rich osmium is released by relatively mild leaching, suggesting the existence of an easily leachable s-process rich presolar phase, or alternatively, of a chemically resistant r-process rich phase. The s-process composition of Os released by mild leaching diverges slightly from that released by aggressive digestion techniques, perhaps suggesting that the presolar phases attacked by these differing procedures condensed in different stellar environments. The correlation between 190Os and 188Os can be used to constrain the s-process 190Os/188Os ratio to be 1.275 pm 0.043. Such a ratio can be reproduced in a nuclear reaction network for a MACS value for 190Os of ~200 pm 22 mbarn at 30 keV. We also present evidence for extensive internal variation of 184Os abundances in the Murchison meteorite. This suggests that p process rich presolar grains (e.g., supernova condensates) may be present in meteorites in sufficient quantities to influence the Os isotopic compositions of the leachates.