Mars core structure—concise review and anticipated insights from insight

Abstract

This review summarizes the knowledge of Mars’ interior structure, its inferred composition, and the anticipated seismological properties arising from its composition with particular focus on Mars’ core. The emphasis on the core stems from the unusual morphology of the liquidus diagram of iron at moderate pressures when enriched in sulfur. From a fairly detailed liquidus diagram constructed from experimental studies, I identify a set of processes that could act within Mars’ core: an iron “snow” from the core-mantle boundary’s surface and a Fe 3−x S 2 “ground fog” forming at the base of the core. Depending on temperature and bulk sulfur composition, these could form an inner core or could stratify the outer core by enriching it in sulfur, or both. Core stratification could be one explanation for the extinction of Mars’ magnetic field early in the planet’s history, and I demonstrate the feasibility of this mechanism. The crystallization processes in the core could be observable in the seismic data that the future Mars geophysical mission, InSight, is planned to provide. The core size, the presence of an inner core, and the wavespeed profile of the outer core, whose radial derivative provides a proxy for changes in composition, are key observables to seek.