Effect of tidal gravity and planetary rotation on the retrieved atmospheric abundances of close-in exoplanets
Abstract
Most modern atmospheric retrievals adopt the simplifying assumption that the planetary atmosphere endures no planetary rotation and stellar tidal effect. However, for tidally locked close-in exoplanets, the gravitational influence of the host star and the rapid rotation of the planet can significantly modify the effective gravity, leading to changes in the atmospheric scale height and mixing ratios of molecular abundances. In this work, we develop a combined framework to include these rotation and tidal effects into a forward and retrieval model to study how they affect the molecular abundances of close-in exoplanets. We specifically apply our model to the planet WASP-12b, observed with HST, and WASP-121b, observed with JWST, and investigate how atmospheric retrieval parameters change when tidal and centrifugal corrections to gravity are included. The forward model calculation for strongly affected gravity in WASP-12b shows an increment in transit depth in the range of 300-600 ppm for major molecules, whereas for WASP-121b with relatively less gravity reduction shows variations of 60-140 ppm. The atmospheric retrievals for both planets with and without effective gravity corrections show differences in the retrieved molecular abundances. To validate the detectability of these gravity-induced changes, we perform synthetic injection-recovery experiments over a broad wavelength range, which show statistically significant shifts in the retrieved atmospheric parameters for simple atmospheric compositions, while more complex atmospheric compositions exhibit smaller changes due to increased retrieval degeneracies. Finally, we investigate the robustness of these results using non-isothermal P-T profiles and cloudy atmospheric models, and find that the inferred trends remain qualitatively consistent.
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BibTeX
@misc{arnav2026effect,
title = {{Effect of tidal gravity and planetary rotation on the retrieved atmospheric abundances of close-in exoplanets}},
author = {K. Arnav and Gopal Hazra},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2606.18100},
eprint = {2606.18100},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.18100},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Effect of tidal gravity and planetary rotation on the retrieved atmospheric abundances of close-in exoplanets
AU - K. Arnav
AU - Gopal Hazra
PY - 2026
DA - 2026/11/04
PB - arXiv
DO - 10.48550/arxiv.2606.18100
UR - https://arxiv.org/abs/2606.18100
AB - Most modern atmospheric retrievals adopt the simplifying assumption that the planetary atmosphere endures no planetary rotation and stellar tidal effect. However, for tidally locked close-in exoplanets, the gravitational influence of the host star and the rapid rotation of the planet can significantly modify the effective gravity, leading to changes in the atmospheric scale height and mixing ratios of molecular abundances. In this work, we develop a combined framework to include these rotation and tidal effects into a forward and retrieval model to study how they affect the molecular abundances of close-in exoplanets. We specifically apply our model to the planet WASP-12b, observed with HST, and WASP-121b, observed with JWST, and investigate how atmospheric retrieval parameters change when tidal and centrifugal corrections to gravity are included. The forward model calculation for strongly affected gravity in WASP-12b shows an increment in transit depth in the range of 300-600 ppm for major molecules, whereas for WASP-121b with relatively less gravity reduction shows variations of 60-140 ppm. The atmospheric retrievals for both planets with and without effective gravity corrections show differences in the retrieved molecular abundances. To validate the detectability of these gravity-induced changes, we perform synthetic injection-recovery experiments over a broad wavelength range, which show statistically significant shifts in the retrieved atmospheric parameters for simple atmospheric compositions, while more complex atmospheric compositions exhibit smaller changes due to increased retrieval degeneracies. Finally, we investigate the robustness of these results using non-isothermal P-T profiles and cloudy atmospheric models, and find that the inferred trends remain qualitatively consistent.
ER -