Distribution of s-, r-, and p-process Nuclides in the Early Solar System Inferred from Sr Isotope Anomalies in Meteorites

Abstract

Nucleosynthetic isotope anomalies in meteorites allow distinguishing between the noncarbonaceous (NC) and carbonaceous (CC) meteorite reservoirs and show that correlated isotope anomalies exist in both reservoirs. It is debated, however, whether these anomalies reflect thermal processing of presolar dust in the disk or are primordial heterogeneities inherited from the solar system’s parental molecular cloud. Here, using new high-precision ^84 Sr isotope data, we show that NC meteorites, Mars, and the Earth and Moon are characterized by the same ^84 Sr isotopic composition. This ^84 Sr homogeneity of the inner solar system contrasts with the well-resolved and correlated isotope anomalies among NC meteorites observed for other elements, and most likely reflects correlated s - and ( r , p )-process heterogeneities leading to ^84 Sr excesses and deficits of similar magnitude, which cancel each other out. For the same reason there is no clearly resolved ^84 Sr difference between NC and CC meteorites, because in some carbonaceous chondrites the characteristic ^84 Sr excess of the CC reservoir is counterbalanced by an ^84 Sr deficit resulting from s -process variations. Nevertheless, most carbonaceous chondrites exhibit ^84 Sr excesses, which reflect admixture of refractory inclusions and more pronounced s -process heterogeneities in these samples. Together, the correlated variation of s - and ( r , p )-process nuclides revealed by the ^84 Sr data of this study refute an origin of these isotope anomalies solely by processing of presolar dust grains, but points to primordial mixing of isotopically distinct dust reservoirs as the dominant process producing the isotopic heterogeneity of the solar system.

Keywords

• Cosmochemistry
• Small Solar System bodies
• Meteorites
• Protoplanetary disks
• Planetary system formation