The shock physics of giant impacts: Key requirements for the equations of state

Sarah T Stewart*, Erik Davies, Megan Duncan, Simon Lock, Seth Root, Joshua Townsend, Richard G. Kraus, Razvan Caracas, Stein B. Jacobsen

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference Contribution (Conference Proceeding)

32 Citations (Scopus)


We discuss major challenges in modeling giant impacts between planetary bodies, focusing on the equations of state (EOS). During the giant impact stage of planet formation, rocky planets are melted and partially vaporized. However, most EOS models fail to reproduce experimental constraints on the thermodynamic properties of the major minerals over the required phase space. Here, we present an updated version of the widely-used ANEOS model that includes a user-defined heat capacity limit in the thermal free energy term. Our revised model for forsterite (Mg2SiO4), a common proxy for the mantles of rocky planets, provides a better fit to material data over most of the phase space of giant impacts. We discuss the limitations of this model and the Tillotson equation of state, a commonly used alternative model.
Original languageEnglish
Title of host publicationAmerican Institute of Physics Conference Proceedings
PublisherAmerican Institute of Physics (AIP)
Publication statusPublished - 4 Nov 2020


  • giant impact
  • Thermodynamics
  • equation of state
  • shock wave physics


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