Impact-induced melting during accretion of the Earth

TL;DR

This study models impact-induced melting during Earth's accretion using N-body simulations to understand how impact parameters influence magma ocean depths and core formation conditions.

Contribution

It introduces a parametrised melting model applied to N-body simulation outputs to analyze melting and metal-silicate equilibration during planetary accretion.

Findings

Magma ocean depths vary with impact velocity and angle.

The duration of magma oceans influences core-mantle differentiation.

Initial conditions in simulations affect melting outcomes.

Abstract

Because of the high energies involved, giant impacts that occur during planetary accretion cause large degrees of melting. The depth of melting in the target body after each collision determines the pressure and temperature conditions of metal-silicate equilibration and thus geochemical fractionation that results from core-mantle differentiation. The accretional collisions involved in forming the terrestrial planets of the inner Solar System have been calculated by previous studies using N-body accretion simulations. Here we use the output from such simulations to determine the volumes of melt produced and thus the pressure and temperature conditions of metal-silicate equilibration, after each impact, as Earth-like planets accrete. For these calculations a parametrised melting model is used that takes impact velocity, impact angle and the respective masses of the impacting bodies into account. The evolution of metal-silicate equilibration pressures (as defined by evolving magma ocean depths) during Earth's accretion depends strongly on the lifetime of impact-generated magma oceans compared to the time interval between large impacts. In addition, such results depend on starting parameters in the N-body simulations, such as the number and initial mass of embryos. Thus, there is the potential for combining the results, such as those presented here, with multistage core formation models to better constrain the accretional history of the Earth.