The EOS/Resolution Conspiracy: Convergence in Proto-Planetary Collision Simulations

Abstract

We investigate how the choice of equation of state (EOS) and resolution conspire to affect the outcomes of giant impact (GI) simulations. We focus on the simple case of equal mass collisions of two Earth-like $0.5M_{\oplus }$ proto-planets showing that the choice of EOS has a profound impact on the outcome of such collisions as well as on the numerical convergence with resolution. In simulations where the Tillotson EOS is used, impacts generate an excess amount of vapour due to the lack of a thermodynamically consistent treatment of phase transitions and mixtures. In oblique collisions this enhances the artificial angular momentum (AM) transport from the planet to the circum-planetary disc reducing the planet's rotation period over time. Even at a resolution of $1.3\times 10^6$ particles the result is not converged. In head-on collisions the lack of a proper treatment of the solid/liquid-vapour phase transition allows the bound material to expand to very low densities which in turn results in very slow numerical convergence of the critical specific impact energy for catastrophic disruption $Q_{RD}^{\ast }$ with increasing resolution as reported in prior work. The simulations where ANEOS is used for oblique impacts are already converged at a modest resolution of $10^5$ particles, while head-on collisions converge when they evidence the post-shock formation of a dense iron-rich ring, which promotes gravitational re-accumulation of material. Once sufficient resolution is reached to resolve the liquid-vapour phase transition of iron in the ANEOS case, and this ring is resolved, the value of $Q_{RD}^{\ast }$ has then converged.

arXiv comment10 pages, 6 figures, 3 tables, accepted for publication in MNRAS

References in corpus (21)

• Catastrophic disruptions revisited
• Gasoline: An adaptable implementation of TreeSPH
• The origin of the Moon within a terrestrial synestia
• Formation of Phobos and Deimos via a Giant Impact
• Forming Mercury by Giant Impacts
• Evidence of a metal-rich surface for the asteroid (16) Psyche from interferometric observations in the thermal infrared
• Consequences of Giant Impacts on Early Uranus for Rotation, Internal Structure, Debris, and Atmospheric Erosion
• Bifurcation in the history of Uranus and Neptune: the role of giant impacts
• Numerical aspects of Giant Impact simulations
• SPH calculations of Mars-scale collisions: the role of the Equation of State, material rheologies, and numerical effects
• Resolution Dependence of Disruptive Collisions between Planetesimals in the Gravity Regime
• Planetary Giant Impacts: Convergence of High-Resolution Simulations using Efficient Spherical Initial Conditions and SWIFT
• Uniformly rotating axisymmetric fluid configurations bifurcating from highly flattened Maclaurin spheroids
• Tidal Evolution of the Evection Resonance/Quasi-Resonance and the Angular Momentum of the Earth-Moon System
• Enhanced mixing in giant impact simulations with a new Lagrangian method
• Primordial Earth mantle heterogeneity caused by the Moon-forming giant impact
• Unconvergence of Very Large Scale GI Simulations
• The Exchange of Mass and Angular Momentum in the Impact Event of Ice Giant Planets: Implications for the origin of Uranus
• Machine learning applied to simulations of collisions between rotating, differentiated planets
• Could Uranus and Neptune form by collisions of planetary embryos?
• Impact Ejecta near the Impact Point Observed using Ultra-high-speed Imaging and SPH Simulations, and a Comparison of the Two Methods

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• A Systematic Survey of Moon-Forming Giant Impacts. II. Rotating bodies
• Exploring the catastrophic regime: thermodynamics and disintegration in head-on planetary collisions
• The Outcome of Collisions between Gaseous Clumps formed by Disk Instability
• The possibility of a giant impact on Venus
• Did Uranus' regular moons form via a rocky giant impactor?