Enriched volatiles and refractories but deficient titanium on the day-side atmosphere of WASP-121b revealed by JWST/NIRISS
Bibliographic record
Abstract
Context . With day-side temperatures elevated enough for all atmospheric constituents to be present in gas form, ultra-hot Jupiters offer a unique opportunity to probe the composition of giant planets. Aims . We aim to infer the composition and thermal structure of the day-side atmosphere of the ultra-hot Jupiter WASP-121b from two NIRISS/SOSS secondary eclipses observed as part of a full phase curve. Methods . We extracted the eclipse spectrum of WASP-121b with two independent data reduction pipelines and analysed it using different atmospheric retrieval prescriptions to explore the effects of thermal dissociation, reflected light, and titanium condensation on the inferred atmospheric properties. Results . We find that the observed day-side spectrum of WASP-121b is best fit by atmosphere models possessing a thermal inversion with temperatures reaching over 3000 K, with spectral contributions from H 2 O, CO, VO, and H − , along with either titanium oxide (TiO) or reflected light. We found the atmosphere of WASP-121b to be metal-enriched (~10× stellar), but comparatively titanium-poor (≲1× stellar), potentially due to partial cold-trapping. The inferred C/O depends on model assumptions, such as whether reflected light is included, ranging from being consistent with stellar, if a geometric albedo of zero is assumed, to being super-stellar for a freely fitted value of Ag = 0.16 −0.02 +0.02 . The volatile-to-refractory ratio was found to be consistent with the stellar value. Conclusions . From the NIRISS eclipse spectrum, we infer that WASP-121b has an atmosphere that is enriched in both volatile and refractory metals, but not in ultra-refractory titanium, suggesting the presence of a night-side cold-trap. Considering H 2 O dissociation is critical in free retrieval analyses, leading to order-of-magnitude differences in retrieved abundances for WASP-121b if neglected. Simple chemical equilibrium retrievals that assume all species are governed by a single metallicity parameter tend to drastically overpredict the TiO abundance, strongly biasing the inferred atmospheric composition.
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 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".