Seismic Detection of a 600-km Solid Inner Core on Mars

Abstract

For rocky planets, the presence of a solid inner core has strong implications for the composition and thermal evolution of the core and for the planet's magnetic history (refs.1-3). On Mars, geophysical observations have confirmed that the core is at least partially liquid (refs.4-7), but it has been unclear whether any part of the core is solid. Here we show from analysis of seismic data acquired by the InSight mission that Mars has a solid inner core. We identify two seismic phases, the deep core-transiting phase, PKKP, and the inner core boundary reflecting phase, PKiKP, indicative of the inner core. Our inversions constrain the radius of the Martian inner core to ~610±50 km, with a compressional velocity jump of ~30% across the inner core boundary. These inner core properties imply a concentration of distinct light elements, supporting inner core crystallization following a “snowing-core” model (ref.8), indicating a relatively low temperature on Mars. This finding provides an anchor point for understanding the thermal and chemical state of Mars. Additionally, the relationship between inner core formation and the Martian magnetic field evolution could offer critical insights into dynamo generation across planetary bodies.