Coupled Orbital and Interior Evolution of Sub-Neptunes
- 1Massachusetts Institute of Technology
- 2MIT Kavli Institute for Astrophysics and Space Research
Abstract
Recent observations have yielded the first measurements of young exoplanet demographics. Close-in sub-Neptune occurrence rates appear to rise from young (10–100 Myr) to intermediate (100 Myr–1 Gyr) ages and then decline sharply in the old (≳1 Gyr) Kepler field population. In this paper, we test whether these observations can be explained by the effects of planetary cooling, atmospheric mass loss, and tidal orbital migration, which we model through a fully coupled evolution framework. The orbital evolution is assumed to operate exclusively through high-eccentricity migration (HEM), in an effort to estimate the maximum possible contribution from this migration channel. In reality, only a subset of planetary systems are expected to undergo HEM. We find that HEM rapidly populates the close-in sub-Neptune bin, producing a sharp rise in occurrence within the first ∼15 Myr. After this early phase, the occurrence evolves only weakly. While the modeled young- to intermediate-age evolution is broadly consistent with the observed trend within the uncertainty limits, it does not support the idea of a sustained young-to-intermediate rise driven by tidal migration. It also fails to reproduce the sharp decline in occurrence seen from intermediate to old ages, motivating additional physics or formation channels to be included in future models.
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BibTeX
@article{sethi2026coupled,
title = {{Coupled Orbital and Interior Evolution of Sub-Neptunes}},
author = {Ritika Sethi and Sarah Millholland and Tim Hallatt},
journal = {The Astrophysical Journal},
year = {2026},
month = oct,
doi = {10.3847/1538-4357/aea905},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea905},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Coupled Orbital and Interior Evolution of Sub-Neptunes
AU - Ritika Sethi
AU - Sarah Millholland
AU - Tim Hallatt
PY - 2026
DA - 2026/10/19
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aea905
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aea905
AB - Recent observations have yielded the first measurements of young exoplanet demographics. Close-in sub-Neptune occurrence rates appear to rise from young (10–100 Myr) to intermediate (100 Myr–1 Gyr) ages and then decline sharply in the old (≳1 Gyr) Kepler field population. In this paper, we test whether these observations can be explained by the effects of planetary cooling, atmospheric mass loss, and tidal orbital migration, which we model through a fully coupled evolution framework. The orbital evolution is assumed to operate exclusively through high-eccentricity migration (HEM), in an effort to estimate the maximum possible contribution from this migration channel. In reality, only a subset of planetary systems are expected to undergo HEM. We find that HEM rapidly populates the close-in sub-Neptune bin, producing a sharp rise in occurrence within the first ∼15 Myr. After this early phase, the occurrence evolves only weakly. While the modeled young- to intermediate-age evolution is broadly consistent with the observed trend within the uncertainty limits, it does not support the idea of a sustained young-to-intermediate rise driven by tidal migration. It also fails to reproduce the sharp decline in occurrence seen from intermediate to old ages, motivating additional physics or formation channels to be included in future models.
SN - 0004-637X
SN - 1538-4357
ER -