The NC-CC Isotope Dichotomy: Implications for the Chemical and Isotopic Evolution of the Early Solar System

Abstract

Understanding the formation of our planetary system requires identification of the materials from which it originated and the accretion processes that produced the planets. The compositional evolution of the solar system can be constrained by synthesizing astronomical datasets and numerical models with elemental and isotopic compositions from objects that directly sampled the disk: meteorites and their constituents (chondrules, refractory inclusions, and matrix). This contribution reviews constraints on early solar system evolution provided by the so-called non-carbonaceous (NC) and carbonaceous chondrite (CC) groups and their relationship to the volatile element characteristics of chondritic meteorites. In previous work, the NC or CC character of a parent body was used to infer its accretion location in the protoplanetary disk. The NC groups purportedly originated in the inner disk, and the CC groups were derived from the outer disk, where the NC and CC regions of the disk may have been separated early on by proto-Jupiter, a pressure maximum, or a dust trap in the disk. The tenet that all CC parent bodies accreted in the outer disk is, in part, based on evidence that a handful of CC meteorites are enriched in volatile species compared to NC meteorites. Here, it is reviewed if and how the volatile element and nucleosynthetic isotope compositions of meteorites can be linked to accretion locations within the disk. The nucleosynthetic isotope compositions of whole rock meteorite samples contrast the trends found for their major volatile element compositions (i.e., C, N, and O). Although there may be an increase in volatile abundances when comparing some stony NC and CC meteorites and their inferred accretion locations within the disk, this is not necessarily a general rule. The difficulties with inferring parent body accretion locations are discussed. It is found that it cannot always be assumed that parent bodies which formed in the CC reservoir are "volatile-rich" relative to those that formed in the NC reservoir which are "volatilepoor". Consequently, tracing the origin of terrestrial volatiles using the NC-CC isotope dichotomy remains challenging.

Origin of Nitrogen Isotopic Variations in the Rocky Bodies of the Solar System

“…The presence of a 15 N-rich chondrite-like N in CAIs also suggests that organic precursors, or at least some of their components, escaped widespread nebular processing . These observations are contrary to the predictions based on the location of soot/tar line, which suggests that organics, including their refractory components, in the inner disk were destroyed within 1 Ma of solar system formation (Bermingham et al 2020;Li et al 2021). A widespread depletion of N in the inner solar system rocky protoplanets and planets despite the presence of organic precursors in the inner protosolar disk attests to the importance of parent body processes like thermal metamorphism, aqueous alteration, core formation, and magma ocean degassing.…”

Implications of Jupiter Inward Gas-driven Migration for the Inner Solar System

“…This separation of the NC and CC groups is often called the NC-CC isotopic dichotomy. Recent results further indicate that CC parent bodies (due to their highly oxidized iron core) formed in a wet environment, i.e., beyond or at the water-ice line, whereas NC parent bodies (with nonoxidized iron cores) formed in a dry environment, i.e., interior to the water-ice line (Bermingham et al 2020;Morbidelli et al 2022). It has also been measured that the amount of CC material delivered for both Earth and Mars was on the order of a few percent in mass (e.g.…”

Origin of hydrogen isotopic variations in chondritic water and organics

“…7 and 8), with refractory organic grains being stable at much higher temperatures (i.e., above 350-450 K) than water-ice grains (i.e., ~160 K, Fig. 7; Nakano et al, 2003;Kuramoto and Yurimoto, 2005;Bermingham et al, 2020). Consequently, the tar line is inward of the snow line, defining three regions in the disk (#1-3, Fig.…”