Evolution of Mercury’s Earliest Atmosphere

Jäggi, Noah; Gamborino, Diana; Bower, Daniel J.; Sossi, Paolo A.; Wolf, Aaron S.; Oza, Apurva V.; Vorburger, Audrey; Galli, André; Wurz, Peter (2021). Evolution of Mercury’s Earliest Atmosphere. The planetary science journal, 2(6), p. 230. IOP Publishing 10.3847/PSJ/ac2dfb

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MESSENGER observations suggest a magma ocean formed on proto-Mercury, during which evaporation of metals and outgassing of C- and H-bearing volatiles produced an early atmosphere. Atmospheric escape subsequently occurred by plasma heating, photoevaporation, Jeans escape, and photoionization. To quantify atmospheric loss, we combine constraints on the lifetime of surficial melt, melt composition, and atmospheric composition. Consideration of two initial Mercury sizes and four magma ocean compositions determines the atmospheric speciation at a given surface temperature. A coupled interior–atmosphere model determines the cooling rate and therefore the lifetime of surficial melt. Combining the melt lifetime and escape flux calculations provides estimates for the total mass loss from early Mercury. Loss rates by Jeans escape are negligible. Plasma heating and photoionization are limited by homopause diffusion rates of ∼106 kg s−1. Loss by photoevaporation depends on the timing of Mercury formation and assumed heating efficiency and ranges from ∼106.6 to ∼109.6 kg s−1. The material for photoevaporation is sourced from below the homopause and is therefore energy limited rather than diffusion limited. The timescale for efficient interior–atmosphere chemical exchange is less than 10,000 yr. Therefore, escape processes only account for an equivalent loss of less than 2.3 km of crust (0.3% of Mercury's mass). Accordingly, ≤0.02% of the total mass of H2O and Na is lost. Therefore, cumulative loss cannot significantly modify Mercury's bulk mantle composition during the magma ocean stage. Mercury's high core:mantle ratio and volatile-rich surface may instead reflect chemical variations in its building blocks resulting from its solar-proximal accretion environment.

Item Type:

Journal Article (Original Article)


08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
08 Faculty of Science > Physics Institute
10 Strategic Research Centers > Center for Space and Habitability (CSH)

UniBE Contributor:

Jäggi, Noah Victor, Gamborino Uzcanga, Diana, Bower, Daniel James, Oza, Apurva Vikram, Vorburger, Audrey Helena, Galli, A, Wurz, Peter


500 Science > 520 Astronomy
600 Technology > 620 Engineering
500 Science > 530 Physics




IOP Publishing




Tina Rothenbühler

Date Deposited:

14 Jan 2022 15:07

Last Modified:

05 Dec 2022 15:57

Publisher DOI:






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