Iron is the dominant element in the cores of terrestrial planets (de Pater & Lissauer, 2015). For Earth it comprises ∼90 wt% of its liquid outer core and ∼97 wt% of solid inner core (Stacey & Davis, 2008). Similar proportions of iron may also be present in the cores of smaller rocky planets like Mercury (Chabot et al., 2014) or more massive exoplanets cataloged as super Earths (Boujibar et al., 2020). Accordingly, thermal properties of iron at high pressures (P) and temperatures (T) are of great significance in Earth and planetary sciences. For instance, thermal equations of states (EoS) of iron are essential for building internal structure models of planets (Anderson &
The observation that mid-ocean ridge basalts had ~3× higher iodine/plutonium ratios (inferred from xenon isotopes) compared to ocean island basalts holds critical insights into Earth’s accretion. Understanding whether this difference stems from core formation alone or heterogeneous accretion is, however, hindered by the unknown geochemical behavior of plutonium during core formation. Here, we use first-principles molecular dynamics to quantify the metal-silicate partition coefficients of iodine and plutonium during core formation and find that both iodine and plutonium partly partition into metal liquid. Using multistage core formation modeling, we show that core formation alone is unlikely to explain the iodine/plutonium difference between mantle reservoirs. Instead, our results reveal a heterogeneous accretion history, whereby predominant accretion of volatile-poor differentiated planetesimals was followed by a secondary phase of accretion of volatile-rich undifferentiated meteorites. This implies that Earth inherited part of its volatiles, including its water, from late accretion of chondrites, with a notable carbonaceous chondrite contribution.
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