The Orbital Eccentricity--Radius Distribution for Warm, Single Planets in TESS

Tyler R. Fairnington; Jiayin Dong; Chelsea X. Huang; Emma Nabbie; George Zhou; Duncan Wright; Karen A. Collins; David Ciardi; Jon M. Jenkins; David W. Latham; George Ricker; Samuel N. Quinn; Sara Seager; Avi Shporer; Roland Vanderspek; Joshua N. Winn; Khalid Barkaoui; Allyson Bieryla; Lars Buchhave; Dmitry Cheryasov; Jessie Christiansen; Courtney Dressing; Akihiko Fukui; Alexey Garmash; Steven Giacalone; Eric G. Hintz; Steve B. Howell; Keisuke Isogai; Jerome de Leon; Jorge Lillo-Box; Felipe Murgas; Norio Narita; Louise D. Nielsen; Enric Palle; Markus Rabus; Benjamin V. Rackham; Richard P. Schwarz; Gregor Srdoc; Denise C. Stephens; Gavin Wang; Noriharu Watanabe; Francis P. Wilkin; Joe Williams

arXiv · 2602.20015

The Orbital Eccentricity--Radius Distribution for Warm, Single Planets in TESS

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Abstract

We characterize the radius-dependent eccentricity distribution of 219 warm (P = 8--50 days) systems with only one transiting planetary candidate identified during Sectors 1-69 of the TESS mission. Using the ``photoeccentric effect'' in a hierarchical Bayesian framework, we first model the population using discrete planetary size bins (sub-Neptunes, sub-Saturns, and Jovians). We then develop a continuous mixture model with weights governed by a logistic sigmoid function of radius. We find that the warm-single population is best described by two components: a dominant low-eccentricity mode ( = 0.039-0.038+0.018) and a secondary dynamically excited mode ( = 0.466-0.068+0.067). The fraction of planets belonging to this high-eccentricity component increases strongly with planet radius, characterized by a transition at a break radius of R_br = 9.2-1.1+1.9 R_e. This trend places warm sub-Saturns predominantly on the same low-eccentricity track as sub-Neptunes. In contrast, warm Jovians (8--16 R_e) are frequently eccentric, with 65-12+13% of the population in the high eccentricity mode. Under the assumption of a two-component model, we see tentative evidence for a bimodal Jovian distribution at ~2.7 sigma. Finally, we identify a non-negligible tail of highly eccentric sub-Neptunes (1--4 R_e), which comprise 16.2-6.4+5.2% of the population, consistent with excitation by non-transiting external companions.

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Tyler R. Fairnington, Jiayin Dong, Chelsea X. Huang, Emma Nabbie, George Zhou, Duncan Wright, Karen A. Collins, David Ciardi, Jon M. Jenkins, David W. Latham, George Ricker, Samuel N. Quinn, Sara Seager, Avi Shporer, Roland Vanderspek, Joshua N. Winn, Khalid Barkaoui, Allyson Bieryla, Lars Buchhave, Dmitry Cheryasov, Jessie Christiansen, Courtney Dressing, Akihiko Fukui, Alexey Garmash, Steven Giacalone, Eric G. Hintz, Steve B. Howell, Keisuke Isogai, Jerome de Leon, Jorge Lillo-Box, Felipe Murgas, Norio Narita, Louise D. Nielsen, Enric Palle, Markus Rabus, Benjamin V. Rackham, Richard P. Schwarz, Gregor Srdoc, Denise C. Stephens, Gavin Wang, Noriharu Watanabe, Francis P. Wilkin, Joe Williams. 2026-07-23. The Orbital Eccentricity--Radius Distribution for Warm, Single Planets in TESS. https://arxiv.org/abs/2602.20015

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