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Dynamical avenues for Mercury’s enigmatic origin

Presentation #106.04 in the session “Impacts, Collisions, and Disruptions”.

Published onJun 01, 2021
Dynamical avenues for Mercury’s enigmatic origin

Mercury’s enigmatic origin continues to puzzle dynamical models. More than that of any of the solar system’s planets Mercury analogs of appropriate mass and sufficient radial offset from Venus are extremely rare within the terrestrial planet formation literature. In practicality, this is simply a result of the initial conditions chosen by such studies; specifically, the truncation the inner terrestrial disk outside of Mercury’s modern orbit and the incorporation of unrealistically massive planet embryos. However, Mercury’s depleted inventory of volatiles and large core seem to suggest that it formed in a different manner than the other terrestrial worlds. While Mercury’s high bulk density has been interpreted to hint that much of its silicate-rich mantle material was eroded in a massive impact, the various proposed collisional scenarios are highly improbable from a dynamical standpoint. Therefore, it is imperative for dynamical models to explore all possible avenues for Mercury’s genesis. In general, there are two types of viable explanations for Mercury’s large iron core: “orderly” scenarios where the planet accretes directly from planetesimals already possessing enriched Fe/Si ratios, and “chaotic” hypotheses where the young Mercury’s once-thicker mantle is violently stripped in an energetic giant impact. We present new results from simulations designed to characterize functional dynamical models for both possible scenarios. While our simulations represent a step forward in terms of the ability of dynamical studies of terrestrial planet formation to simultaneously reconcile Mercury’s mass, orbit and composition, the precise solar system result remains somewhat of an outlier within the spectrum of numerically generated outcomes. Nevertheless, our results are promising in terms of their consistent ability to generate Mercury-Venus pairs, and several of our simulations generate remarkably accurate inner solar system analogs.

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