^1,2Dongyang Huang,^1,3Julien Siebert,²Paolo Sossi,¹Edith Kubik,¹Guillaume Avice,²Motohiko Murakami
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.05.010]
¹Institut de Physique du Globe de Paris, 75005 Paris, France
²Institute of Geochemistry and Petrology, ETH Zürich, 8092 Zürich, Switzerland
³Institut Universitaire de France, 75005 Paris, France
Copyright Elsevier

Nitrogen (N) is the most abundant element in Earth’s atmosphere, but is extremely depleted in the silicate Earth. However, it is not clear whether core sequestration or early atmospheric loss was responsible for this depletion. Here we study the effect of core formation on the inventory of nitrogen using laser-heated diamond anvil cells. We find that, due to the simultaneous dissolution of oxygen in the metal, N becomes much less siderophile (iron-loving) at pressures and temperatures up to 104 GPa and 5000 K, a thermodynamic condition relevant to the bottom of the magma ocean in the aftermath of the moon-forming giant impact. Using a core-mantle-atmosphere coevolution model, we show that the impact-induced processes (core formation and/or atmospheric loss) are unlikely to account for the observed N anomaly, which is instead best explained by the accretion of mainly N-poor impactors. The terrestrial volatile pattern requires severe N depletion on precursor bodies, prior to their accretion to the proto-Earth.

¹D. J. Joswiak,¹D. E. Brownlee,²A. J. Westphal,²Z. Gainsforth,³M. Zhang,³N. T. Kita
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14187]
¹Department of Astronomy, University of Washington, Seattle, Washington, USA
²Space Sciences Laboratory, University of California, Berkeley, California, USA
³WiscSIMS, Department of Geoscience, University of Wisconsin–Madison, Madison, Wisconsin, USA
Published by arrangement with John Wiley & Sons

A literature compilation of 1136 low-Ca pyroxene compositions from chondrules from 12 primitive type 2–3 carbonaceous, ordinary and enstatite chondrite groups define unique regions on an Al2O3 and Cr2O3 diagram when compared to low-Ca pyroxenes from equilibrated type 4-6 chondrites. Measured compositions of 100 low-Ca pyroxenes from comet Wild 2 and a giant cluster IDP of probable cometary origin are similar to each other and fall in the type 2–3 chondrite chondrule region suggesting that most of the pyroxenes likely formed in the solar nebula like conventional chondrules. The data imply that most low Ca-pyroxenes from comet Wild 2 and the giant cluster IDP formed from igneous crystallization processes and did not experience significant thermal metamorphism, indicating that the low-Ca pyroxenes were unlikely incorporated into large parent bodies prior to accretion in their respective comet bodies. An intriguing group of nine low-Ca pyroxenes from comet Wild 2 with low Cr and Al that fall where type 4–6 chondrites are located are interpreted as products of condensation. The compositional data combined with previously measured oxygen isotopes on 17 low-Ca pyroxenes support earlier conclusions that comet samples have links with carbonaceous, ordinary, and possibly enstatite chondrite groups. Our results provide additional evidence that comets accreted materials from multiple chondrule reservoirs throughout the solar nebula.