  Impacts between planetary-sized bodies can explain the origin of satellites
orbiting large ($R>500$~km) trans-Neptunian objects. Their water rich
composition, along with the complex phase diagram of water, make it important
to accurately model the wide range of thermodynamic conditions material
experiences during an impact event and in the debris disk. Since differences in
the thermodynamics may influence the system dynamics, we seek to evaluate how
the choice of an equation of state (EOS) alters the system's evolution.
Specifically, we compare two EOSs that are constructed by different approaches:
either by a simplified analytic description (Tillotson), or by interpolation of
tabulated data (Sesame). Approximately $50$ pairs of Smoothed Particle
Hydrodynamics impact simulations were performed, with similar initial
conditions but different EOSs, in the parameter space in which the Pluto-Charon
binary is thought to form (slow impacts between Pluto-size, water rich bodies).
Generally, we show that impact outcomes (e.g., circumplanetary debris disk) are
consistent between EOSs. Some differences arise, importantly in the production
of satellitesimals (large intact clumps) that form in the post-impact debris
disk. When utilizing an analytic EOS, the emergence of satellitesimals is
highly certain, while when using the tabulated EOS it is less common. This is
because for the typical densities and energies experienced in these impacts,
the analytic EOS predicts very low pressure values, leading to particles
artificially aggregating by a tensile instability.
