The Chemical Composition of Mercury

TL;DR

This paper discusses Mercury's surface composition revealed by MESSENGER, indicating a more reducing formation environment and providing insights into its core and mantle composition, which are crucial for understanding planetary formation.

Contribution

It presents new surface composition data of Mercury from MESSENGER, challenging existing formation models and offering estimates of its mantle and core composition.

Findings

Mercury has high abundances of volatile elements and low iron content.

The planet's composition suggests formation under reducing conditions.

Mercury's core is likely Si-rich and enriched in Fe and S.

Abstract

The chemical composition of a planetary body reflects its starting conditions modified by numerous processes during its formation and geological evolution. Measurements by X-ray, gamma-ray, and neutron spectrometers on the MESSENGER spacecraft revealed Mercury's surface to have surprisingly high abundances of the moderately volatile elements sodium, sulfur, potassium, chlorine, and thorium, and a low abundance of iron. This composition rules out some formation models for which high temperatures are expected to have strongly depleted volatiles and indicates that Mercury formed under conditions much more reducing than the other rocky planets of our Solar System. Through geochemical modeling and petrologic experiments, the planet's mantle and core compositions can be estimated from the surface composition and geophysical constraints. The bulk silicate composition of Mercury is likely similar to that of enstatite or metal-rich chondrite meteorites, and the planet's unusually large core is most likely Si rich, implying that in bulk Mercury is enriched in Fe and Si (and possibly S) relative to the other inner planets. The compositional data for Mercury acquired by MESSENGER will be crucial for quantitatively testing future models of the formation of Mercury and the Solar System as a whole, as well as for constraining the geological evolution of the innermost planet.