Artist's depiction of possible interiors for Mars which the Insight Lander mission will explore
Mars has an iron-rich core, silicate mantle, thin silicate crust and atmosphere. The thickness of the crust can be estimated using variations in gravitational field experienced by orbiters, and the topography maps from the Mars Global Surveyor laser altimeter. However the results depend on the density contrasts between core and mantle and are not unique, and there may also be further unresolved layering From geophysical models there may be two or more phase changes in the minerals that make up its interior. The satellite measurements seem to indicate a large and possibly liquid core but its size is not known.
The measurements from the Insight lander will help clarify this.