Most Super-Earths Have Less Than 3% Water


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Date

2025-01-20

Publication Type

Journal Article

ETH Bibliography

yes

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Abstract

Super-Earths are highly irradiated, small planets with bulk densities approximately consistent with Earth. We construct combined interior atmosphere models of super-Earths that trace the partitioning of water throughout a planet, including an iron-rich core, silicate-rich mantle, and steam atmosphere. We compare these models with exoplanet observations to infer a 1 sigma upper limit on the total water mass fraction of less than or similar to 3% at the population level. We consider end-member scenarios that may change this value, including the efficiency of mantle outgassing, escape of high mean molecular weight atmospheres, and increased iron core mass fractions. Although our constraints are agnostic as to the origin of water, we show that our upper limits are consistent with its production via chemical reactions of primordial hydrogen-dominated atmospheres with magma oceans. This mechanism has also been hypothesised to explain Earth's water content, possibly pointing to a unified channel for the origins of water on small terrestrial planets.

Publication status

published

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Volume

979 (1)

Pages / Article No.

79

Publisher

IOP Publishing

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Edition / version

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Funding

211313 - Planets and their deep volatile reservoirs (SNF)
205606 - NCCR PlanetS / Externship M.R. (SNF)

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