Atmospheric composition and circulation of the ultra-hot Jupiter WASP-121b with joint NIRPS, HARPS and CRIRES+ transit spectroscopy
Bibliographic record
Abstract
Ultra-hot gas giants such as WASP-121b provide unique laboratories for exploring atmospheric chemistry and dynamics under extreme irradiation conditions. Uncovering their chemical composition and atmospheric circulation is critical for tracing planet formation pathways. Here, we present a comprehensive atmospheric characterisation of WASP-121b using high-resolution transit spectroscopy across the optical to infrared with HARPS, NIRPS, and CRIRES+ spanning nine transit events. These observations are complemented with five TESS photometric sectors, two EulerCam light curves simultaneous to the HARPS and NIRPS transits, and an extensive radial velocity dataset in order to refine WASP-121b's orbital parameters. A cross-correlation analysis detected iron (Fe), carbon monoxide (CO) and vanadium (V) absorption signals with SNR of 5.8, 5.0, and 4.7, respectively. Our retrieval analysis constrains the water (H 2 O) abundance to −6.52 −0.68 +0.49 dex, although its absorption signal is effectively muted by the hydride (H − ) continuum. We constrained the relative abundances of the volatile and refractory elements - which represents a crucial diagnostic of atmospheric chemistry, evolution, and planet formation pathways. The retrieved abundance ratios are broadly consistent with expected values of a solar composition atmosphere in chemical equilibrium, likely indicating minimal disequilibrium chemistry alterations at the probed pressures (∼10 −4 −10 −3 bar). We update the orbital parameters of WASP-121b with its largest radial velocity dataset to date. By comparing orbital velocities derived from both the radial velocity analysis and the atmospheric retrieval, we determined a non-zero velocity offset caused by atmospheric circulation, ΔK p = −15 ± 3 km s −1 (assuming M ⋆ = 1.38 ± 0.02 M ⊙ ), consistent with predictions from either drag-free or weak-drag 3D global circulation models, while we caution the non-negligible dependence on the assumed stellar mass. These results place new constraints on the thermal structure, dynamics, and chemical inventory of WASP-121b, highlighting the power of multi-wavelength high-resolution spectroscopy to probe exoplanetary atmospheres.
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".