Atmospheric loss in giant impacts depends on pre-impact surface conditions

Simon Lock*, Sarah T Stewart

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

Abstract

Earth likely acquired much of its inventory of volatile elements during the main stage of its formation. Some of Earth's proto-atmosphere must therefore have survived the giant impacts, collisions between planet-sized bodies, that dominate the latter phases of accretion. Here we use a suite of 1D hydrodynamic simulations and impedance match calculations to quantify the effect that pre-impact surface conditions (such as atmospheric pressure and presence of an ocean) have on the efficiency of atmospheric and ocean loss from proto-planets during giant impacts. We find that -- in the absence of an ocean -- lighter, hotter, and lower-pressure atmospheres are more easily lost. The presence of an ocean can significantly increase the efficiency of atmospheric loss compared to the no-ocean case, with a rapid transition between low and high loss regimes as the mass ratio of atmosphere to ocean decreases. However, contrary to previous thinking, the presence of an ocean can also reduce atmospheric loss if the ocean is not sufficiently massive, typically less than a few times the atmospheric mass. Volatile loss due to giant impacts is thus highly sensitive to the surface conditions on the colliding bodies. To allow our results to be combined with 3D impact simulations, we have developed scaling laws that relate loss to the ground velocity and surface conditions. Our results demonstrate that the final volatile budgets of planets are critically dependent on the exact timing and sequence of impacts experienced by their precursor planetary embryos, making atmospheric properties a highly stochastic outcome of accretion.
Original languageEnglish
Article number28
JournalThe Planetary Science Journal
Volume5
Issue number28
DOIs
Publication statusPublished - 1 Feb 2024

Bibliographical note

Funding Information:
The authors acknowledge the late, great Jay Melosh for useful discussions and stimulating questions on the topic of atmospheric loss. S.J.L. thanks Erik Asphaug and Hidenori Genda for help in replicating the results of Genda & Abe (2005) using the Tillotson EOS, and Matthew Roche for his feedback on earlier versions of the manuscript. We also thank Hidenori Genda and an anonymous reviewer for their encouraging and constructive comments, which helped improve the manuscript. S.J.L. acknowledges the support of an NASA Earth and Space Science Fellowship (grant No. NNX13AO67H), the NSF (awards EAR-1947614 and EAR-1725349), the Earth and Planetary Science Department of Harvard University, the Division of Geological and Planetary Sciences of the California Institute of Technology, and the UK Natural Environment Research Council (grant No. NE/V014129/1). S.T.S. acknowledges support from NASA through grant Nos. 80NSSC18K0828 and NNX15AH54G. This work was carried out using the FASRC Odyssey cluster, supported by the FAS Division of Science Research Computing Group at Harvard University, and the computational facilities of the Advanced Computing Research Centre, University of Bristol.

Funding Information:
The authors acknowledge the late, great Jay Melosh for useful discussions and stimulating questions on the topic of atmospheric loss. S.J.L. thanks Erik Asphaug and Hidenori Genda for help in replicating the results of Genda & Abe () using the Tillotson EOS, and Matthew Roche for his feedback on earlier versions of the manuscript. We also thank Hidenori Genda and an anonymous reviewer for their encouraging and constructive comments, which helped improve the manuscript. S.J.L. acknowledges the support of an NASA Earth and Space Science Fellowship (grant No. NNX13AO67H), the NSF (awards EAR-1947614 and EAR-1725349), the Earth and Planetary Science Department of Harvard University, the Division of Geological and Planetary Sciences of the California Institute of Technology, and the UK Natural Environment Research Council (grant No. NE/V014129/1). S.T.S. acknowledges support from NASA through grant Nos. 80NSSC18K0828 and NNX15AH54G. This work was carried out using the FASRC Odyssey cluster, supported by the FAS Division of Science Research Computing Group at Harvard University, and the computational facilities of the Advanced Computing Research Centre, University of Bristol.

Publisher Copyright:
© 2024. The Author(s). Published by the American Astronomical Society.

Keywords

  • Shock
  • planet formation
  • Cosmochemistry
  • Accretion
  • Earth atmosphere
  • Collisional processess
  • Planetary atmospheres

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