Habitable Zones & Global Climate

Impact Induced Atmosphere-Mantle Exchange Sets The Volatile Elemental Ratios On Primitive Earths

By Keith Cowing
July 26, 2022
Filed under
Impact Induced Atmosphere-Mantle Exchange Sets The Volatile Elemental Ratios On Primitive Earths
Volatile mass accreted/eroded (a) and mass degassed/ingassed (b) with a growing Earth. We randomly sample one out of 104 planetesimals and document the volatile mass transferred during each impact event. Marker size denotes impactor radius.

Conventional planet formation theory suggests that chondritic materials have delivered crucial atmospheric and hydrospheric elements such as carbon (C), nitrogen (N), and hydrogen (H) onto primitive Earth.

However, recent measurements highlight the significant elemental ratio discrepancies between terrestrial parent bodies and the supposed planet building blocks. Here we present a volatile evolution model during the assembly of Earth and Earth-like planets. Our model includes impact losses, atmosphere-mantle exchange, and time dependent effects of accretion and outgassing calculated from dynamical modeling outcomes.

Exploring a wide range of planetesimal properties (i.e., size and composition) as well as impact history informed by N-body accretion simulations, we find that while the degree of CNH fractionation has inherent stochasticity, the evolution of C/N and C/H ratios can be traced back to certain properties of the protoplanet and projectiles.

Interestingly, the majority of our Earth-like planets acquire superchondritic final C/N ratios, implying that the volatile elemental ratios on terrestrial planets are driven by the complex interplay between delivery, atmospheric ablation, and mantle degassing.

Howard Chen, Seth A. Jacobson

Comments: 24 pages, 10 figures, 3 tables; accepted to Earth and Planetary Science Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2207.13087 [astro-ph.EP] (or arXiv:2207.13087v1 [astro-ph.EP] for this version)
Submission history
From: Howard Chen
[v1] Tue, 26 Jul 2022 17:58:32 UTC (8,826 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) 🖖🏻