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Auteurs principaux: Schulze, Joseph, Hinkel, Natalie, Panero, Wendy, Unterborn, Cayman
Format: Preprint
Publié: 2026
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Accès en ligne:https://arxiv.org/abs/2601.13176
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author Schulze, Joseph
Hinkel, Natalie
Panero, Wendy
Unterborn, Cayman
author_facet Schulze, Joseph
Hinkel, Natalie
Panero, Wendy
Unterborn, Cayman
contents The bulk compositions of small planets ($R_p< 2 \mathrm{R}_\oplus$) are directly linked to their formation histories, making reliable compositional constraints imperative for testing models of planet formation and evolution. Because exoplanet interiors cannot be directly observed, their make-up must be inferred from mass-radius-composition models that link assumed stellar abundances to the direct observables: planetary mass and radius. There are a variety of such models in the literature, each adopting different equations of state (EOS) to describe the materials' properties at depth and varying assumptions about the minerals present within the planets. These EOS+mineral suites provide the foundations for compositional inferences, but they have not yet been systematically compared. In this work, we review several suites, with a detailed description of the basic structure, mineral physics, and materials within standard small planet models. We show that EOS+mineral suites predict planet densities whose differences are comparable to current observational uncertainties, which present a challenge for robustly interpreting and classifying small planets. We apply a powerful small-planet characterization framework, which illustrates that variations among EOS+mineral suites lead to inconsistent conclusions for both individual planets and sample-level demographics. Our results demonstrate the need for more careful considerations of the materials and EOS used in mass-radius-composition models, especially given the current focus on finding and characterizing potentially habitable rocky planets. We conclude with recommendations for best practices so that future interpretations of small planets and their formation are accurate and consistent.
format Preprint
id arxiv_https___arxiv_org_abs_2601_13176
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Toward Reliable Interpretations of Small Exoplanet Compositions: Comparisons and Considerations of Equations of State and Materials Used in Common Rocky Planet Models
Schulze, Joseph
Hinkel, Natalie
Panero, Wendy
Unterborn, Cayman
Earth and Planetary Astrophysics
The bulk compositions of small planets ($R_p< 2 \mathrm{R}_\oplus$) are directly linked to their formation histories, making reliable compositional constraints imperative for testing models of planet formation and evolution. Because exoplanet interiors cannot be directly observed, their make-up must be inferred from mass-radius-composition models that link assumed stellar abundances to the direct observables: planetary mass and radius. There are a variety of such models in the literature, each adopting different equations of state (EOS) to describe the materials' properties at depth and varying assumptions about the minerals present within the planets. These EOS+mineral suites provide the foundations for compositional inferences, but they have not yet been systematically compared. In this work, we review several suites, with a detailed description of the basic structure, mineral physics, and materials within standard small planet models. We show that EOS+mineral suites predict planet densities whose differences are comparable to current observational uncertainties, which present a challenge for robustly interpreting and classifying small planets. We apply a powerful small-planet characterization framework, which illustrates that variations among EOS+mineral suites lead to inconsistent conclusions for both individual planets and sample-level demographics. Our results demonstrate the need for more careful considerations of the materials and EOS used in mass-radius-composition models, especially given the current focus on finding and characterizing potentially habitable rocky planets. We conclude with recommendations for best practices so that future interpretations of small planets and their formation are accurate and consistent.
title Toward Reliable Interpretations of Small Exoplanet Compositions: Comparisons and Considerations of Equations of State and Materials Used in Common Rocky Planet Models
topic Earth and Planetary Astrophysics
url https://arxiv.org/abs/2601.13176