[S19-4] Science goals and modeling of the Insight/SEIS experiment

[S19-4-02] Mars' core and what its seismological structure could reveal about the planet's evolution

^○George Helffrich (Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo, Japan)

If the meteorite-based inferences of Mars' core composition are correct, it could show peculiar structural features compared to Earth's core. The liquidus diagram of iron at moderate pressures when enriched in sulfur is unusual for a core sulfur content of 11-17 wt%. 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; its feasibility will be discussed. 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.