Fig. 1: Seismic properties of the core as seen with InSight and from first-principles simulations.

Comparison of seismic profiles from InSight with results from first-principles simulations. a,b, Density (a) and P-wave velocity (b) profiles of liquid Fe and liquid Fe–Ni–S–C–O–H senary mixtures in Mars’s core obtained from AIMD simulations and InSight observations. The blue shaded profiles represent the predicted seismic core properties based on magnetic (that is, spin-polarized) and non-magnetic (that is, non-spin-polarized) AIMD simulations³, including the effects of variations in temperature (±200 K), for the core composition (comprising 67.7% Fe, 5.5% Ni, 7.2% S, 15.1% C, 3.8% O and 0.7% H by weight) that best fits the mean of the InSight seismic profiles within ±2σ at the CMB (indicated by the light orange vertical bar labelled ‘CMB’), corresponding to a radius in the range 1,790–1,840 km (ref. ²). The orange shaded profiles represent the predicted seismic core properties based on magnetic and non-magnetic AIMD simulations, including the effects of variations in temperature (±200 K), for the core composition (comprising 69.9% Fe, 5.7% Ni, 14.6% S, 4.3% C, 4.7% O and 0.8% H by weight) that best fits the mean of the InSight seismic profiles within ±2σ at approximately 800 km in the core (indicated by the light orange vertical bar labelled ‘Inside core’). The labelled C values indicate the C contents of the best-fitting solutions at the CMB and at a depth of around 800 km in the core, respectively. As the orange and blue profiles do not overlap, no single composition exists that matches the InSight observations simultaneously at the CMB and in the core (Methods and Extended Data Fig. 4). Note that the width of the vertical light orange bars has no physical significance.