arXiv subjects

Gabriel Nathan

Publications and source records attributed to Gabriel Nathan.

3 recordsLinked to original sources

arXiv2026

Magnitude of stable iron isotope fractionation limited by multiple stages of terrestrial core formation

One proposed mechanism for generating iron isotopic differences between planetary mantles and chondrites is metal-silicate equilibration during terrestrial core formation. Prior studies of this isotopic fractionation effect employ single-stage core formation models that are inconsistent with reproducing the siderophile element budget of the Earth's mantle. Here, we model iron isotopic evolution of the Earth's mantle in a multistage core formation scenario that is consistent with dynamic models of planet formation and reproduces the geochemistry of the bulk silicate Earth, specifically the refractory moderately siderophile elements. We find that multiple stages of core formation rebalance the fractionating effect of metal-silicate equilibration for the iron isotopic system, comparable to or smaller than typical analytical uncertainties in mantle rocks. Ultimately, this rebalancing effect - coupled with stochastic accretion and differentiation histories which further complicate planetary formation processes - makes it unlikely that isotopic fractionation during metal-silicate equilibration is the primary mechanism responsible for the iron isotopic composition of the Earth's mantle.

astro-ph.EP↗

arXiv2026

Oxidation Constraints on Terrestrial Planet Formation from a Ring

The present-day solar system comprises meteorites with varying oxidation levels, derived from different parent bodies. Previous studies (e.g. Rubie et al., 2011) of the partitioning of siderophile elements between mantle and core during planetary growth and differentiation showed that Earth must accrete reduced bodies first and oxidised bodies later. Here we show that, if the terrestrial planets formed from a narrow ring of planetesimals, this condition is not fulfilled, whatever heliocentric gradient of oxidation is assumed in the ring. The reason is that planetary embryos quickly accrete planetesimals from the whole width of the ring, incorporating both reduced and oxidised material. The partially oxidised state of all planetary embryos leads to mismatches with the composition of the bulk silicate Earth (BSE) because oxygen fugacity strongly affects the partitioning of siderophile elements. We demonstrate that reproducing the BSE composition requires reduced and oxidised reservoirs to remain segregated until embryo formation is almost complete. The delivery of oxidised material to the terrestrial planet-forming ring towards the end of the disc's lifetime is therefore a key requirement of any successful dynamical model of terrestrial planet formation.

astro-ph.EP↗

arXiv2023

Constraining the Origin of Mars via Simulations of Multi-Stage Core Formation

It remains an elusive goal to simultaneously model the astrophysics of Solar System accretion while reproducing the mantle chemistry of more than one inner terrestrial planet. Here, we used a multistage core-mantle differentiation model based on Rubie et al. (2011,2015) to track the formation and composition of Earth and Mars in various Grand Tack formation simulations. Prior studies showed that in order to recreate Earth's mantle composition, it must grow first from reduced (Fe-metal rich and O-poor) building blocks and then from increasingly oxidized (FeO rich) material. This accretion chemistry occurs when an oxidation gradient exists across the disk so that the innermost solids are reduced and increasingly oxidized material is found at greater heliocentric distances. For a suite of Grand Tack simulations, we investigated whether Earth and Mars can be simultaneously produced by the same oxidation gradient. Our model did not find an oxidation gradient that simultaneously reproduces the mantle composition of Earth and Mars. Due to its small mass and rapid formation, the formation history of Mars-like planets is very stochastic which decreases the likelihood of compatibility with an Earth-producing oxidation gradient in any given realization. To reconcile the accretion history and ideal chemistry of the Mars-like planet with the oxidation gradient of an Earth-producing disk, we determined where in the Earth-producing disk Mars must have formed. We find that the FeO-rich composition of the Martian mantle requires that Mars' building blocks must originate exterior to 1.0 astronomical units (AU).

astro-ph.EP↗