Hypothetical hyperbolic encounters between Venus and proto-Mercury that partially \ stripped away proto-Mercury's mantle

TL;DR

This study simulates hyperbolic encounters between proto-Mercury and proto-Venus, showing that such interactions can strip proto-Mercury's mantle and produce the planet's current iron-rich composition, highlighting their role in planetary formation.

Contribution

It introduces a novel simulation of hyperbolic encounters that can explain Mercury's large core without high-temperature impacts, emphasizing their significance in planetary accretion models.

Findings

Proto-Mercury's mantle can be stripped by hyperbolic encounters.

Multiple encounters with fast-spinning projectiles can produce Mercury's current iron fraction.

Encounters can lead to diverse outcomes like orbital decay and binary planets.

Abstract

Mercury has an unusually large metal core comprising ~70% of its mass comparing to all other terrestrial planets in the solar system. Giant impacts can remove a significant fraction of the silicate mantle of a chondritic proto-Mercury and form the iron rich present-day Mercury. However, such high-temperature giant impacts seem at odds with the retainment of moderately volatile elements on present-day Mercury (Peplowski et al. 2011). We simulated a series of hyperbolic encounters between proto-Mercury and proto-Venus, which may occur in the chaotic early solar system. Tidal disruption of proto-Mercury always removes part of its silicate mantle while its iron core remains intact. We find, in favourable cases, four close encounters with fast spinning projectiles (resulting from previous encounters) can lead to present-day Mercury iron fraction. More encounters are needed when the spin and orbital angular momentum are not always aligned. These hyperbolic encounters have various outcomes, such as orbital decay, binary planets and change of spin rates. These results suggest the importance of proper treatment of close encounters in N-body simulations of planetary accretion.