  There is a direct relation between the composition of a host star and that of
the planets orbiting around it. As such, the recent discovery of stars with
unusual chemical composition, notably enriched in carbon instead of oxygen,
support the existence of exoplanets with a chemistry dominated by carbides
instead of oxides. Accordingly several studies have been recently conducted on
the Si C binary system at high pressure and temperature. Nonetheless, the
properties of carbides at the P T conditions of exoplanets interiors are still
inadequately constrained, effectively hampering reliable planetary modeling.
Here we present an in situ X ray diffraction study of the Si C binary system up
to 200 GPa and 3500 K, significantly enlarging the pressure range explored by
previous experimental studies. The large amount of collected data allows us to
properly investigate the phase diagram and to refine the Clapeyron slope of the
transition line from the zinc blende to the rock salt structure. Furthermore
the pressure volume temperature equation of state are provided for the high
pressure phase, characterized by low compressibility and thermal expansion. Our
results are used to model idealized C rich exoplanets of end members
composition. In particular, we derived mass radius relations and performed
numerical simulations defining rheological parameters and initial conditions
which lead to onset of convection in such SiC planets. We demonstrate that if
restrained to silicate rich mantle compositions, the interpretation of mass
radius relations may underestimate the interior diversity of exoplanets.
