We present the first static measurements of the density of metallic liquids
in the Fe-S system in the pressure and temperature range 1.5 GPa-6.2 GPa a
nd 1500 K - 1780 K. Density is inferred from X-ray absorption experiments c
arried out with a large volume press at the European Synchrotron Radiation
Facility. It is shown that increasing the amount of sulfur in liquid iron d
ecreases the bulk incompressibility by -2.5 GPa per 1 weight% of S. These d
ata are important for constraining the presence and amount of sulfur in the
cores of small planetary bodies.