TOI-2109: An Ultrahot Gas Giant on a 16 hr Orbit
Bibliographic record
Abstract
Abstract We report the discovery of an ultrahot Jupiter with an extremely short orbital period of 0.67247414 ± 0.00000028 days (∼16 hr). The 1.347 ± 0.047 R Jup planet, initially identified by the Transiting Exoplanet Survey Satellite (TESS) mission, orbits TOI-2109 (TIC 392476080)—a T eff ∼ 6500 K F-type star with a mass of 1.447 ± 0.077 M ☉, a radius of 1.698 ± 0.060 R ☉, and a rotational velocity of v sin i * = 81.9 ± 1.7 km s−1. The planetary nature of TOI-2109b was confirmed through radial-velocity measurements, which yielded a planet mass of 5.02 ± 0.75 M Jup. Analysis of the Doppler shadow in spectroscopic transit observations indicates a well-aligned system, with a sky-projected obliquity of λ = 1.°7 ± 1.°7. From the TESS full-orbit light curve, we measured a secondary eclipse depth of 731 ± 46 ppm, as well as phase-curve variations from the planet’s longitudinal brightness modulation and ellipsoidal distortion of the host star. Combining the TESS-band occultation measurement with a K s -band secondary eclipse depth (2012 ± 80 ppm) derived from ground-based observations, we find that the dayside emission of TOI-2109b is consistent with a brightness temperature of 3631 ± 69 K, making it the second hottest exoplanet hitherto discovered. By virtue of its extreme irradiation and strong planet–star gravitational interaction, TOI-2109b is an exceptionally promising target for intensive follow-up studies using current and near-future telescope facilities to probe for orbital decay, detect tidally driven atmospheric escape, and assess the impacts of H2 dissociation and recombination on the global heat transport.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".