Evolution of the first atmosphere of Mercury

Evolution of the first atmosphere of Mercury

Press release from: arXiv.org e-Print archive
Posted: Tuesday October 19 2021

Noah Jäggi, Diana Gamborino, Dan J. Bower, Paolo A. Sossi, Aaron S. Wolf, Apurva V. Oza, Audrey Vorburger, André Galli, Peter Wurz

MESSENGER’s observations suggest that an ocean of magma formed on proto-Mercury, during which the evaporation of metals and the degassing of volatiles containing C and H produced an early atmosphere. Atmospheric exhaust then occurred through plasma heating, photoevaporation, Jeans exhaust, and photoionization. To quantify atmospheric losses, we combine constraints on the life of the surface melt, the composition of the melt and the atmospheric composition. Taking into account two initial sizes of Mercury and four oceanic compositions of magma determines atmospheric speciation at a given surface temperature. A coupled indoor atmosphere model determines the cooling rate and therefore the service life of the surface iron. The combination of cast iron life and exhaust flow calculations provides estimates of the total mass loss of the onset of Mercury. Jeans escape loss rates are negligible. Plasma heating and photoionization are limited by homopause diffusion rates of ∼106 kg / s. The photoevaporative loss depends on the time of mercury formation and the assumed heating efficiency and ranges from ∼106.6 to 109.6 kg / s. The material for photoevaporation comes from below the homopause and is therefore limited in energy rather than diffusion. The timescale for efficient chemical exchange between the interior and the atmosphere is less than ten thousand years. Therefore, the escape processes only represent an equivalent loss of less than 2.3 km of crust (0.3% of the mass of Mercury). As a result, ≤0.02% of the total mass of H2O and Na is lost. Therefore, the cumulative loss cannot significantly change the composition of the bulk mantle of Mercury during the oceanic magmatic phase. Rather, Mercury’s high core-to-mantle ratio and volatile-rich surface may reflect chemical variations in its building blocks resulting from its solar-proximal accretion environment.

Comments: 25 pages, 8 figures, accepted for publication in The Planetary Science Journal

Topics: Terrestrial and planetary astrophysics (astro-ph.EP)

Quote as: arXiv: 2110.08093 [astro-ph.EP] (or arXiv: 2110.08093v1 [astro-ph.EP] for this version)

History of submissions

From: Noah Jäggi

[v1] Fri 15 Oct 2021 13:41:43 UTC (2,224 KB)

https://arxiv.org/abs/2110.08093

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