Dependence on the Equation of State in SPH Simulations of Proto-Uranian Disk Formation from a Giant Impact

The 98 obliquity of Uranus is widely attributed to a giant impact that ejected material and formed a debris disk, which subsequently coalesced into its regular satellites. Previous Smoothed Particle Hydrodynamics (SPH) studies have yielded inconsistent disk compositions, a discrepancy often linked to the variety of numerical and physical modeling assumptions. We address this by presenting SPH simulations that systematically test three distinct EOS models alongside two SPH schemes (standard SPH, and the enhanced density-independent SPH). We utilized a 3M impactor and explored a range of impact parameters which are capable of reproducing Uranus's current spin state. Our primary finding is that for impacts capable of reproducing Uranus's current rotation, the choice of EOS or SPH scheme barely affects macroscopic features such as the post-impact rotation period, disk mass, or disk size; these properties are primarily controlled by the impact's angular momentum. In contrast, the disk's rock fraction is highly EOS-dependent. Our results clarify that while disk mass and size are robust outcomes, the final disk composition is highly model-dependent. Therefore, accurate EOS modeling, integrated with detailed disk evolution studies, is essential to definitively validate the giant impact scenario for Uranus.