JWST and HST Confirm Transit Timing Variations for the Ultra-Hot Jupiter TOI-2109 b
Abstract
Ultra-hot Jupiters are a rare yet valuable subset of exoplanets that can help elucidate both the internal properties of their host stars as well as the orbital evolution of close-in planets. An extreme among extremes, TOI-2109 b is a super-Jupiter (1.347 ± 0.047 RJup, 5.02 ± 0.75 MJup) with the shortest orbital period (0.67247479 ± 0.00000028 days) and the fastest predicted orbital decay rate of any known giant planet. Previous observations hinted at a quadratic long-term trend in the transit timing variations (TTVs) consistent with orbital decay, as well as short-term sinusoidal TTVs consistent with a near-resonant planetary companion that would indicate a dynamically quiescent migration pathway. Here, we combine archival ground-based, TESS, and CHEOPS photometry with new transit and eclipse data from HST and JWST to update the TTV analysis. We find very strong evidence for sinusoidal TTVs over a linear ephemeris (ΔBIC of 33.6), consistent with a nearby planetary companion as suggested by J.-V. Harre et al. 2024, and rule out several non-planetary scenarios that could explain the sinusoidal TTVs. We also find strong evidence of a quadratic TTV trend (ΔBIC of 6.75) consistent with an orbital decay rate of -3.46 ± 1.17 ms/yr and a stellar tidal quality factor of 2.13+1.18−0.61 ×107, though we cannot rule out line-of-sight acceleration as the cause of the quadratic trend. If our results are confirmed, TOI-2109 b would be the only known exoplanet besides WASP-12 b with a decaying orbit and the most extreme of an ultra-rare class of close-in giant planets with nearby companions.
Related
- Prospects for detecting hot-Jupiter tidal decay through transit timing with the mission Earth 2.0
- ExoEcho: Exoplanet Ephemerides Change Observations. III. A JWST Survey for Transit Timing Variations of 37 Exoplanets
- ExoEcho: Exoplanet Ephemerides Change Observations. III. A JWST Survey for Transit Timing Variations of 37 Exoplanets
- Evidence for LP 890-9d via Transit Timing Variations
- ExoMOD II. A Statistical Model of Transit Timing Variations in Kepler Multi-Planet Systems
BibTeX
@misc{greklekmckeon2026jwst,
title = {{JWST and HST Confirm Transit Timing Variations for the Ultra-Hot Jupiter TOI-2109 b}},
author = {Michael Greklek-McKeon and Julie Inglis and Nicole L. Wallack and Shreyas Vissapragada and Ian Wong and John R. T. Allen and Yayaati Chachan and Fei Dai and Guangwei Fu and Tiffany Kataria and Thaddeus D. Komacek and Johanna K. Teske},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.26894},
eprint = {2609.26894},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.26894},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - JWST and HST Confirm Transit Timing Variations for the Ultra-Hot Jupiter TOI-2109 b
AU - Michael Greklek-McKeon
AU - Julie Inglis
AU - Nicole L. Wallack
AU - Shreyas Vissapragada
AU - Ian Wong
AU - John R. T. Allen
AU - Yayaati Chachan
AU - Fei Dai
AU - Guangwei Fu
AU - Tiffany Kataria
AU - Thaddeus D. Komacek
AU - Johanna K. Teske
PY - 2026
DA - 2026/09/22
PB - arXiv
DO - 10.48550/arxiv.2609.26894
UR - https://arxiv.org/abs/2609.26894
AB - Ultra-hot Jupiters are a rare yet valuable subset of exoplanets that can help elucidate both the internal properties of their host stars as well as the orbital evolution of close-in planets. An extreme among extremes, TOI-2109 b is a super-Jupiter (1.347 ± 0.047 R_Jup, 5.02 ± 0.75 M_Jup) with the shortest orbital period (0.67247479 ± 0.00000028 days) and the fastest predicted orbital decay rate of any known giant planet. Previous observations hinted at a quadratic long-term trend in the transit timing variations (TTVs) consistent with orbital decay, as well as short-term sinusoidal TTVs consistent with a near-resonant planetary companion that would indicate a dynamically quiescent migration pathway. Here, we combine archival ground-based, TESS, and CHEOPS photometry with new transit and eclipse data from HST and JWST to update the TTV analysis. We find very strong evidence for sinusoidal TTVs over a linear ephemeris (ΔBIC of 33.6), consistent with a nearby planetary companion as suggested by J.-V. Harre et al. 2024, and rule out several non-planetary scenarios that could explain the sinusoidal TTVs. We also find strong evidence of a quadratic TTV trend (ΔBIC of 6.75) consistent with an orbital decay rate of -3.46 ± 1.17 ms/yr and a stellar tidal quality factor of 2.13^+1.18_−0.61 ×10^7, though we cannot rule out line-of-sight acceleration as the cause of the quadratic trend. If our results are confirmed, TOI-2109 b would be the only known exoplanet besides WASP-12 b with a decaying orbit and the most extreme of an ultra-rare class of close-in giant planets with nearby companions.
ER -