MARSA key piece of evidence when considering the core is whether or not Mars has a magnetic field. The early Mars probes saw a bow shock at around 5000km radius which implies a balance of solar wind with an iono- or magneto-pause at 25 gamma. This implies a very small magnetic field, if any. The upper limit after allowing for gas pressure would be of the order 10-5of the earth's. It has only been with recent probes that a very weak magnetic field has been confirmed. This is so weak it cannot prevent ingress of the solar wind into the upper atmosphere, so the boundary is little different from an ionopause. A pure Fe or Fe-Ni core would be solid. An FeS core, or better still an Fe-FeS mix, would melt at Fe-FeS eutectic temperatures and so would allow it to still be partly molten. It is still a matter of conjecture whether the Bfield seen requires a liquid core. The detailed gravitational potential structure suggets that the crust is well-compensated on large
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