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

Abstract

Noncarbonaceous (NC; inner solar system) meteorites have lower 15N/14N ratios than carbonaceous (CC; outer solar system) meteorites. Whether this is evidence of a primordial heterogeneity of N reservoirs in the protosolar disk remains unclear. In this study, I consider the N isotopic compositions of meteorite (chondrite, achondrite, and iron meteorite) parent bodies as a function of their growth zones. Despite the 15N/14N ratios of CC meteorites being generally higher than NC meteorites, there is a substantial overlap between them. Late-stage mixing of isotopically distinct reservoirs cannot explain this overlap. 15N/14N ratios of meteorites, independent of the growth zones, are correlated with the accretion ages of their parent bodies. A common correlation of the 15N/14N ratios of NC and CC chondrites with their peak metamorphic temperatures suggests that N isotopic compositions of meteorites were likely set by a universal time-dependent process—thermal evolution of their parent bodies by radiogenic heating. Therefore, heterogeneous N isotopic compositions of meteorites do not allude to isotopically heterogeneous primitive N reservoirs in the protosolar disk. Rather, it is likely that the N isotopic compositions of meteorites are a direct reflection of a differential response of labile 15N-rich and refractory 15N-poor components in common organic precursors to variable degrees of parent body processing. Consequently, the isotopic ratios of N, and other highly volatile elements like C and H, in meteorites do not reflect the isotopic compositions of primitive volatile reservoirs in the protosolar disk and thus cannot be used independently to cosmolocate volatile reservoirs in the disk.

Exoplanet Volatile Carbon Content as a Natural Pathway for Haze Formation

“…Alternatively, Hirschmann et al (2021) argued that heating of planetesimals from radioactive decay ( 26 Al in our solar system) can reach high enough temperatures to destroy the organics and drive off volatiles. If Earth's building blocks formed later than suggested by Li et al (2021), the low carbon content of the Earth could then be a result of the differentiation and thermal metamorphism of its progenitors, which we readily see in the meteorite record (see also Grewal 2022).…”

The distribution of volatile elements during rocky planet formation

“…Frontiers in Earth Science frontiersin.org it was present in early planetary building blocks (Marty, 2012;Grewal, et al, 2021b;Grewal, 2022;Grewal and Asimow, 2023). Its depletion in Earth's mantle relative to C (Marty, 2012) suggests that N could have been incorporated into the Earth's core.…”

“…Crucially, heterogeneous models driven by the mass delivery scenarios of N-body simulations tend to favor the delivery of more volatile-rich materials, ultimately sourced from the outer Solar System, later in the accretion process when the potential for extreme P-T metal-silicate reactions is at its maximum (Halliday, 2013;O'Brien, et al, 2014;Rubie, et al, 2016). However, analyses of small rocky bodies and coupled to astrophysical and geochemical models suggest that volatile elements were present in the inner Solar System well before the later stages of planetary formation (Bar-Nun and Owen, 1998;Busemann, et al, 2006;Marty, 2012;Halliday, 2013;Alexander, 2017;McCubbin and Barnes, 2019;Grewal, et al, 2021c;Deligny, et al, 2021;Grewal, 2022;Grewal and Asimow, 2023).…”

Origin of nitrogen on Mars: First in situ N isotope analyses of martian meteorites

“…Although cometary 15 N/ 14 N and D/H ratios have only been determined remotely for a limited number of molecules (i.e., HCN, CN, and NH 2 for 15 N/ 14 N; e.g., Bockelée-Morvan et al, 2015, and references therein), these observations indicate that cometary ices are significantly enriched in the heavy isotopes 15 N and D compared to the solar nebula and chondrites. It should also be noted, however, that chondrite groups show a range of nitrogen and hydrogen isotopic compositions because parent body processes (aqueous alteration and/or thermal metamorphism) modified initial isotopic signatures (e.g., Piani et al, 2020;Grewal, 2022).…”