Super-Earth Interiors Shrink by About 10% as They Crystallise
Abstract
Super-Earth exoplanets are among the most abundant planets known, yet their bulk densities leave the interior state degenerate. The static structure models used to interpret them, and the interior retrievals built on them, typically describe the cold, solidified end state of an evolution that begins hot and molten. During this magma ocean stage the interior, the outgassed atmosphere, and the surface co-evolve and set the long-term climate and geophysics of super-Earths. We develop and validate a fully coupled model for the structural and thermal evolution of super-Earth exoplanets within the PROTEUS framework, including new and upgraded models of the interior structure, mantle energetics, and volatile outgassing. In volatile-poor super-Earths of 1 to 10 Earth masses, the silicate interior contracts by about 10 % of its molten radius through cooling and crystallisation, nearly independent of planet mass and driven by the thinning silicate shell alone. The solidified radius is set by planetary mass and core fraction, insensitive to the host star, irradiation, and initial thermal state. In contrast, volatile-rich super-Earths at and above about 5 Earth masses may not solidify: their thick outgassed atmospheres throttle the surface heat loss until the interior settles into a deep magma ocean, keeping the planet inflated and limiting the contraction to about half its volatile-poor value. Mantle contraction alone thus shapes the low-mass exoplanet transit population, motivating joint interpretation of atmospheric and geophysical signatures in upcoming exoplanet surveys.
Related
- Searching for hot water world candidates with CHEOPS. II. A low-density super-Earth orbiting the K dwarf TOI-2211
- Reflation: redox-driven atmospheric inflation as tracer of super-Earth geochemistry
- Detection and characterization of the temperate super-earth Gliese 48 b
- Dynamical Behavior and Surface Features of Large Super-Fast Rotator Near-Earth Asteroid (436724) 2011 UW158
- Orbital Architecture of Super-Earth-Cold-Jupiter Systems from Transit Duration Ratios
BibTeX
@misc{lichtenberg2026superearth,
title = {{Super-Earth Interiors Shrink by About 10% as They Crystallise}},
author = {Tim Lichtenberg and Mara Attia and Harrison Nicholls and Mariana Sastre and Dan J. Bower and Karen Stuitje and Flavia C. Pascal and Laurent Soucasse and Daniel Apai and Patrick Bos and Robb Calder and Lorenzo Cesario and Lisa Dang and Emeline Decocq and Marijn van Dijk and Mohammad Farhat and Kaustubh Hakim and Tadahiro Kimura and Imre Kisvárdai and Sebastiaan Krijt and Yamila Miguel and Ioannis Panagiotou and Emma Postolec and Martin Schlecker and Sara Seager and Anat Shahar and Oliver Shorttle and Paolo A. Sossi and Wim van Westrenen},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.23091},
eprint = {2609.23091},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.23091},
}
RIS
TY - UNPB
TI - Super-Earth Interiors Shrink by About 10% as They Crystallise
AU - Tim Lichtenberg
AU - Mara Attia
AU - Harrison Nicholls
AU - Mariana Sastre
AU - Dan J. Bower
AU - Karen Stuitje
AU - Flavia C. Pascal
AU - Laurent Soucasse
AU - Daniel Apai
AU - Patrick Bos
AU - Robb Calder
AU - Lorenzo Cesario
AU - Lisa Dang
AU - Emeline Decocq
AU - Marijn van Dijk
AU - Mohammad Farhat
AU - Kaustubh Hakim
AU - Tadahiro Kimura
AU - Imre Kisvárdai
AU - Sebastiaan Krijt
AU - Yamila Miguel
AU - Ioannis Panagiotou
AU - Emma Postolec
AU - Martin Schlecker
AU - Sara Seager
AU - Anat Shahar
AU - Oliver Shorttle
AU - Paolo A. Sossi
AU - Wim van Westrenen
PY - 2026
DA - 2026/09/19
PB - arXiv
DO - 10.48550/arxiv.2609.23091
UR - https://arxiv.org/abs/2609.23091
AB - Super-Earth exoplanets are among the most abundant planets known, yet their bulk densities leave the interior state degenerate. The static structure models used to interpret them, and the interior retrievals built on them, typically describe the cold, solidified end state of an evolution that begins hot and molten. During this magma ocean stage the interior, the outgassed atmosphere, and the surface co-evolve and set the long-term climate and geophysics of super-Earths. We develop and validate a fully coupled model for the structural and thermal evolution of super-Earth exoplanets within the PROTEUS framework, including new and upgraded models of the interior structure, mantle energetics, and volatile outgassing. In volatile-poor super-Earths of 1 to 10 Earth masses, the silicate interior contracts by about 10 % of its molten radius through cooling and crystallisation, nearly independent of planet mass and driven by the thinning silicate shell alone. The solidified radius is set by planetary mass and core fraction, insensitive to the host star, irradiation, and initial thermal state. In contrast, volatile-rich super-Earths at and above about 5 Earth masses may not solidify: their thick outgassed atmospheres throttle the surface heat loss until the interior settles into a deep magma ocean, keeping the planet inflated and limiting the contraction to about half its volatile-poor value. Mantle contraction alone thus shapes the low-mass exoplanet transit population, motivating joint interpretation of atmospheric and geophysical signatures in upcoming exoplanet surveys.
ER -