Phase Curves of Hot Neptune LTT 9779b Suggest a High-metallicity Atmosphere
Bibliographic record
Abstract
Abstract Phase-curve measurements provide a global view of the composition, thermal structure, and dynamics of exoplanet atmospheres. Although most of the dozens of phase-curve measurements made to date are of large, massive hot Jupiters, there is considerable interest in probing the atmospheres of the smaller planets that are the more typical endproduct of the planet formation process. One such planet that is favorable for these studies is the ultrahot Neptune LTT 9779b, a rare denizen of the Neptune desert. A companion paper presents the planet’s secondary eclipses and dayside thermal emission spectrum; in this work we describe the planet’s optical and infrared phase curves, characterized using a combination of Spitzer and Transiting Exoplanet Survey Satellite (TESS) photometry. We detect LTT 9779b’s thermal phase variations at 4.5 μm, finding a phase amplitude of 358 ± 106 ppm and no significant phase offset, with a longitude of peak emission occurring −10° ± 21° east of the substellar point. Combined with our secondary eclipse observations, these phase-curve measurements imply a 4.5 μm dayside brightness temperature of 1800 ± 120 K, a nightside brightness temperature of 700 ± 430 K (<1350 K at 2σ confidence), and a day–night brightness temperature contrast of 1110 ± 460 K. We compare our data to the predictions of 3D general circulation models calculated at multiple metallicity levels and to similar observations of hot Jupiters experiencing similar levels of stellar irradiation. Though not conclusive, our measurement of its small 4.5 μm phase offset, the relatively large amplitude of the phase variation, and the qualitative differences between our target’s dayside emission spectrum and those of hot Jupiters of similar temperatures all suggest a supersolar atmospheric metallicity for LTT 9779b, as might be expected given its size and mass. Finally, we measure the planet’s transits at both 3.6 μm and 4.5 μm, providing a refined ephemeris (P = 0.79207022 ± 0.00000069 days, T 0 = 2458783.51636 ± 0.00027, BJDTDB) that will enable efficient scheduling of future observations to further characterize the atmosphere of this intriguing planet.
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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 | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".