Relic interstellar grains in Murchison meteorite

Abstract

Isotopic analyses of hydrogen, carbon and nitrogen in meteorites provide important information about the origin and history of these elements both in meteorites and in the Solar System. Here we show that, in the Murchison meteorite, the D/H ratios of hydrogen are unusually high in several separates and in one case up to 30 times the cosmic value of 2 × 10⁻⁵. Many phases show high ¹³C/¹²C ratios, up to 2.5 times the terrestrial value of 0.011. These ¹³C-rich and D-rich components of the two chemical elements are not correlated. Also they are heterogeneously distributed, suggesting that different components in the meteorite originated from different astrophysical sites and at different times. The D-rich hydrogen in the meteorite is probably due to molecules formed by ion–molecule reactions in interstellar clouds while the tiny amount of ¹³C-rich carbon is probably due to nucleosynthesis in red giant stars as suggested by Swart et al.¹. Both of these heavy-isotope enriched components survived homogenization in the accumulation and subsequent history of the meteorites.