Giant impacts stochastically change the internal pressures of terrestrial planets
Pressure is a key parameter in the physics and chemistry of planet formation and evolution. Previous studies have erroneously assumed that internal pressures monotonically increase with the mass of a body. Using smoothed particle hydrodynamics and potential field method calculations, we demonstrate that the hot, rapidly rotating bodies produced by giant impacts can have much lower internal pressures than cool, slowly rotating planets of the same mass. Pressures subsequently increase because of thermal and rotational evolution of the body. Using the Moon-forming impact as an example, we show that the internal pressures after the collision could have been less than half that in present-day Earth. The current pressure profile was not established until Earth cooled and the Moon receded, a process that may take up to tens of millions of years. Our work defines a new paradigm for pressure evolution during accretion of terrestrial planets: stochastic changes driven by impacts.
Additional Information© 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution License 4.0 (CC BY). Submitted 10 September 2018; Accepted 2 August 2019; Published 4 September 2019. We are grateful to two anonymous reviewers for comments that helped improve the quality of this manuscript. We also thank J. Jackson and P. Asimow for useful discussions. This work was supported by NESSF grant NNX13AO67H (to S.J.L.), NASA grant NNX15AH54G (to S.T.S.), and DOE-NNSA grant DE-NA0002937 (to S.T.S.). S.J.L. also acknowledges support from Harvard University's Earth and Planetary Sciences Department and Caltech's Division of Geological and Planetary Sciences. Author contributions: S.T.S. performed the SPH calculations. S.J.L. performed the HERCULES calculations, analyzed all simulation output, and wrote the paper. Both authors discussed the results and contributed to the ideas in the paper. The authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. The modified version of GADGET-2 and the equation of state tables are contained in the supplementary materials of (23). The HERCULES code is included in the supporting information of (2) and is available through the GitHub repository (https://github.com/sjl499/HERCULESv1_user).
Published - eaav3746.full.pdf
Accepted Version - 2006.01992.pdf
Supplemental Material - aav3746_SM.pdf
Supplemental Material - aav3746_Table_S1.csv