Detection of CO <sub>2</sub> , CO, and H <sub>2</sub> O in the atmosphere of the warm sub-Saturn HAT-P-12 b
Bibliographic record
Abstract
Context . The chemical composition of warm gas giant exoplanet atmospheres (with T eq < 1000 K) is not well known due to the lack of observational constraints. Aims . HAT-P-12 b is a warm, sub-Saturn-mass transiting exoplanet that is ideal for transmission spectroscopy. We aim to characterise its atmosphere and probe the presence of carbonaceous species using near-infrared observations. Methods . One transit of HAT-P-12 b was observed in spectroscopy with JWST NIRSpec in the 2.87–5.10 µm range with a resolving power of ~1000. The JWST data are combined with archival observations from HST WFC3 covering the 1.1–1.7 µm range. The data were analysed using two data reduction pipelines and two atmospheric retrieval tools. Atmospheric simulations using chemical forward models were performed to interpret the spectra. Results . CO 2 , CO, and H 2 O are detected at 12.2, 4.1, and 6.0 σ confidence, respectively. Their volume mixing ratios are consistent with an atmosphere of ~10× solar metallicity and production of CO 2 by photochemistry. CH 4 is not detected and seems to be lacking, which could be due to a high intrinsic temperature with strong vertical mixing or other phenomena. SO 2 is also not detected and its production seems limited by low upper atmosphere temperatures (~500 K at P ≲ 10 −3 bar derived from one-dimensional retrievals), insufficient to produce it in detectable quantities (≳ 800 K required according to photochemical models). H 2 S is marginally detected using one data analysis method, but not by the other. Retrievals indicate the presence of clouds between 2 and 11 mbar using one data analysis method, and between 5 and 269 mbar using the other. The derived C/O ratio is below unity, but is not well constrained. Conclusions . This study points towards an atmosphere for HAT-P-12 b that could be enriched in carbon and oxygen with respect to its host star, a possibly cold upper atmosphere that may explain the non-detection of SO 2 , and a CH 4 depletion that is yet to be fully understood. When including the production of CO 2 via photochemistry, an atmospheric metallicity that is close to Saturn’s can explain the observations. Metallicities inferred for other gas giant exoplanets based on their CO 2 mixing ratios may need to account for its photochemical production pathways. This may impact studies on mass-metallicity trends and links between exoplanet atmospheres, interiors, and formation history.
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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 | 0.000 | 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) | 0.001 | 0.000 |
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".