The origin and evolution of a blastered Mercury

Introduction

Mercury is a metal-rich planet from which Earth-based and spacecraft data were collected. Our understanding of its interior structure and thermochemical evolution is, however, still relatively poor.

Challenges in Understanding Mercury

This is due to:

1. Large uncertainties on its polar moment of inertia and surface composition; this will be largely improved by the BepiColombo mission.
2. An unknown bulk-planet composition.
3. A poor knowledge of some key thermophysical properties (e.g., phase stability, temperature, density) of solid/liquid metals and silicates inside Mercury.

This is because under Mercury’s reducing conditions, elements behave differently than on other planets. Currently available phase diagrams for the Moon and Mars are thus irrelevant for calculating the compositions and physical properties of Mercury’s core, mantle, and crust. Improving such constraints is critical but requires new experiments under hitherto unexplored conditions; they will be done in IronHeart.

Hypothesis of Proto-Mercury

So far, it was largely neglected that many compositional features of Mercury are inconsistent with its direct accretion as a small, metal-rich planet. IronHeart’s working hypothesis is that Mercury is merely the remnant of a larger, Martian-sized, chondritic planet (which we call proto-Mercury) involved in collisions that have stripped away much of its mantle. This process did eventually set the final composition of modern Mercury.

Experimental Evaluation

For the first time, IronHeart will evaluate experimentally how proto-Mercury controlled the core and mantle compositions of modern Mercury. Further experiments on these compositions will provide phase equilibria of Mercury’s internal layers, allowing us to calculate their thermophysical properties.

Integration with BepiColombo Data

By combining those with BepiColombo data into thermal and geophysical models, we will provide a clearer than ever picture of Mercury’s structure and evolution. IronHeart will also be critical to understanding dense exoplanets and the Earth, which accreted from similar building blocks as Mercury.