Impact events

Reduced Atmospheres Of Post-impact Worlds: The Early Earth

By Keith Cowing
April 22, 2022
Filed under
Reduced Atmospheres Of Post-impact Worlds: The Early Earth
Left: Vertical slice of the target and impactor (impact angle of 45◦ ) before the impact takes place, showing the mantles and cores of both bodies, as well as the target’s surface conditions, Right: decision tree showing the components of the physical model included in each of the five models presented in Section 5.

Impacts may have had a significant effect on the atmospheric chemistry of the early Earth. Reduced phases in the impactor (e.g., metallic iron) can reduce the planet’s H2O inventory to produce massive atmospheres rich in H2.

Whilst previous studies have focused on the interactions between the impactor and atmosphere in such scenarios, we investigate two further effects, 1) the distribution of the impactor’s iron inventory during impact between the target interior, target atmosphere, and escaping the target, and 2) interactions between the post-impact atmosphere and the impact-generated melt phase. We find that these two effects can potentially counterbalance each other, with the melt-atmosphere interactions acting to restore reducing power to the atmosphere that was initially accreted by the melt phase.

For a ∼1022kg impactor, when the iron accreted by the melt phase is fully available to reduce this melt, we find an equilibrium atmosphere with H2 column density ∼104molescm−2 (pH2∼120bars, XH2∼0.77), consistent with previous estimates. However, when the iron is not available to reduce the melt (e.g., sinking out in large diameter blobs), we find significantly less H2 (7×102−5×103molescm−2, pH2≲60bars, XH2≲0.41). These lower H2 abundances are sufficiently high that species important to prebiotic chemistry can form (e.g., NH3, HCN), but sufficiently low that the greenhouse heating effects associated with highly reducing atmospheres, which are problematic to such chemistry, are suppressed. The manner in which iron is accreted by the impact-generated melt phase is critical in determining the reducing power of the atmosphere and re-solidified melt pool in the aftermath of impact.

J. P. Itcovitz, A. S. P. Rae, R. I. Citron, S. T. Stewart, C. A. Sinclair, P. B. Rimmer, O. Shorttle

Comments: 34 Pages, 11 Figures, 3 Appendices, Accepted for publication in PSJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2204.09946 [astro-ph.EP (or arXiv:2204.09946v1 [astro-ph.EP] for this version)
Submission history
From: Jonathan Itcovitz
[v1] Thu, 21 Apr 2022 08:13:59 UTC (868 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻