The Distribution Of Volatile Elements During Rocky Planet Formation

By Keith Cowing
Status Report
December 3, 2023
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The Distribution Of Volatile Elements During Rocky Planet Formation
Schematic contours of H, C, and N speciation determined by Raman spectroscopy in basaltic glasses synthesized in piston-cylinder experiments at 1–2 GPa and 1,400°C–1,600°C, shown as a function of fO2 (relative to the IW buffer) and H content (as equivalent H2O, wt. %). Raman and FTIR measurements are from Hirschmann (2012), Armstrong et al. (2015), Dalou et al. (2019, 2022), and Grewal et al. (2020). Blank areas represent conditions at which literature data are currently lacking. This figure demonstrates that H, C, and N on their own may be present as multiple species at a given fO2 or water content, and that they combine to form different molecules in natural and synthetic glasses. fO2 of Earth and Mars formation are indicated. Sulfur speciation is not shown because the effect of H on S speciation has not yet been determined at fO2 relevant to magma ocean conditions. — astro-ph.EP

Core segregation and atmosphere formation are two of the major processes that redistribute the volatile elements-hydrogen (H), carbon (C), nitrogen (N), and sulfur (S)-in and around rocky planets during their formation.

The volatile elements by definition accumulate in gaseous reservoirs and form atmospheres. However, under conditions of early planet formation, these elements can also behave as siderophiles (i.e., iron-loving) and become concentrated in core-forming metals.

Current models of core formation suggest that metal-silicate reactions occurred over a wide pressure, temperature, and compositional space to ultimately impose the chemistries of the cores and silicate portions of rocky planets.

Additionally, the solubilities of volatile elements in magmas determine their transfer between the planetary interiors and atmospheres, which has recently come into sharper focus in the context of highly irradiated, potentially molten exoplanets. Recently, there has been a significant push to experimentally investigate the metal-silicate and magma-gas exchange coefficients for volatile elements over a wide range of conditions relevant to rocky planet formation.

Qualitatively, results from the metal-silicate partitioning studies suggest that cores of rocky planets could be major reservoirs of the volatile elements though significant amounts will remain in mantles. Results from solubility studies imply that under oxidizing conditions, most H and S are sequestered in the magma ocean, while most N is outgassed to the atmosphere, and C is nearly equally distributed between the atmosphere and the interior.

Under reducing conditions, nearly all N dissolves in the magma ocean, the atmosphere becomes the dominant C reservoir, while H becomes more equally distributed between the interior and the atmosphere, and S remains dominantly in the interior.

Terry-Ann Suer, Colin Jackson, Damanveer S. Grewal, Celia Dalou, Tim Lichtenberg

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (; Geophysics (physics.geo-ph)
Cite as: arXiv:2311.18262 [astro-ph.EP] (or arXiv:2311.18262v1 [astro-ph.EP] for this version)
Journal reference: Front. Earth Sci. 11:1159412 2023
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From: Terry-Ann Suer
[v1] Thu, 30 Nov 2023 05:44:03 UTC (2,814 KB)

Astrobiology, Astrochemistry,

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