TRAPPIST-1

Uncertainties In The Inference of Internal Structure: The Case of TRAPPIST-1 f

By Keith Cowing

Status Report

astro-ph.EP

April 24, 2025

Filed under astro-ph.EP, atmosphere, exoplanet, habitability, TRAPPIST-1, TRAPPIST-1 f

Uncertainties In The Inference of Internal Structure: The Case of TRAPPIST-1 f — Left, difference in wmf between two different hydrosphere assumptions and the default model. Red dotted is models with the surface temperature raised to create a layer of liquid water instead of ice Ih. Blue dashed is models with the AQUA compilation of EoSs from Haldemann et al. (2020). The hatched region shows the 1-σ region of wmf from observational uncertainties with our default model. Right, difference in wmf between planet models with different bulk moduli for the mantle or core and our default planet model. In red, the bulk modulus of the core is increased (dotted) and decreased (dashed) by 10%. In blue, the bulk modulus of the bridgmanite and post perovskite is increased/decreased by 10%. — astro-ph.EP

We use the TRAPPIST-1 system as a model observation of Earth-like planets. The densities of these planets being 1-10% less than the Earth suggest that the outer planets may host significant hydrospheres.

We explore the uncertainty in water mass fraction from observed mass and radius. We investigate the interior structure of TRAPPIST-1 f using the open-source solver MAGRATHEA and varying assumptions in the interior model.

We find that TRAPPIST-1 f likely has a water mass fraction of 16.2% ± 9.9% when considering all possible core mass fractions and requires 6.9% ± 2.0% water at an Earth-like mantle to core ratio.

We quantify uncertainties from observational precision, model assumptions, and experimental and theoretical data on the bulk modulus of planet building materials.

We show that observational uncertainties are smaller than model assumptions of mantle mineralogy and core composition but larger than hydrosphere, temperature, and equation of state assumptions/uncertainties.

Our findings show that while precise mass and radius measurements are crucial, uncertainties in planetary models can often outweigh those from observations, emphasizing the importance of refining both theoretical models and experimental data to better understand exoplanet interiors.

David R. Rice, Chenliang Huang, Jason H. Steffen, Allona Vazan

Comments: 18 pages, 8 figures, 3 tables, Accepted in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2504.16201 [astro-ph.EP] (or arXiv:2504.16201v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2504.16201
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Submission history
From: David Rice
[v1] Tue, 22 Apr 2025 18:47:58 UTC (3,896 KB)
https://arxiv.org/abs/2504.16201

Astrobiology,

Keith Cowing

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) 🖖🏻

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