No Venus-like atmosphere on TRAPPIST-1 c: confirmation from 3D climate modelling
Bibliographic record
Abstract
Recent measurements of the dayside thermal emission of exoplanets TRAPPIST-1b [1] and TRAPPIST-1c [2] were made by the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) F1500W filter which covers the 15-µm carbon dioxide (CO2) absorption. These photometric secondary-eclipse observations determined the dayside brightness temperature and constrained the magnitude of heat redistribution. For TRAPPIST-1c, which has a Venus-like stellar irradiation, the estimated eclipse depth is 421±94 ppm, corresponding to a dayside brightness temperature of 380±31 K, superior to Venus's equilibrium temperature. Two scenarios stem from the inferred brightness temperature: a moderate heat redistribution or an airless, non-zero bond albedo surface. The observations rendered thick, CO2-enriched atmospheres unlikely for TRAPPIST-1c, excluding a cloudy (sulphuric acid aerosols) and a clear-sky Venus-like atmosphere at a confidence of 2.6σ and 3.0σ, respectively [2].New JWST observations (Cycle 2 GO Programme 3077) [3] will obtain thermal emission phase curve measurements for most of TRAPPIST-1c’s orbit (P = 58-hours), identifying the day-night temperature contrast. These will be sensitive to test the case of a moderate heat redistribution [4-8], eventually distinguishing it from spectral features from a rocky surface or those from an airless planet [9]. This research is crucial given that CO2–dominated atmospheres were predicted as a likely outcome of atmospheric evolution on rocky planets orbiting cooler and less massive stars (M-dwarf stars) than our Sun [10]. Owing to the CO2 high molecular weight and efficient cooling in the infrared, CO2-rich atmospheres have extremely cold thermospheres and less expanded upper atmospheres; both can improve resilience to atmospheric escape processes, offering partial protection against M-dwarf lifelong stellar activity [10]. Investigating the status of a possible atmosphere on TRAPPIST-1c is critical to understanding atmospheric evolution on M-dwarf planets.Here, we use a 3D global circulation model of the atmosphere, the Generic-PCM [8,11-13], to simulate a modern Venus-like atmosphere on TRAPPIST-1c: CO2-dominated, 92-bar surface pressure with radiatively-active global cover of sulphuric acid aerosols [13]. We also assumed a tidally-locked planet with zero obliquity and eccentricity. We use these simulations to generate high spectral resolution thermal phase curves for three JWST/MIRI filters: F1280W, F1500W and F1800W. We analyse the relationship between phase curve parameters (hot spot offset and amplitude), temperature and large-scale circulation. We find large eastward offsets and small amplitudes compatible with an efficient day-night heat redistribution driven by a superrotating equatorial jet. In addition, we predict a smaller hot spot offset for F1500W due to upper atmosphere CO2 absorption. These results highlight the possibility of studying at least two different atmospheric levels. The absence of a large hot spot offset on TRAPPIST-1c would rule out a dense, CO2-rich, absorbing atmosphere on the planet. These results can be expanded to the ever-growing population of rocky exoplanets with Venus-like stellar irradiations to be studied in the following decades [14].References: [1]Greene+2023.Nature.618; [2]Zieba+2023.Nature.620; [3]Gillon+2023.JWST Proposal 3077; [4]Selsis+2011.A&A.532; [5]Demory+2016.Nature.532; [6]Koll+2016.ApJ.825; [7]Kreidberg+2019.Nature.573; [8]Turbet+2016.A&A.596.A112; [9]Whittaker+2022.AJ.164; [10]Turbet+2020.Space Sci. Rev.216; [11]Forget & Leconte, 2014.Phil.Trans R.Soc.A372; [12]Wordsworth+2011.ApJL.733.L48; [13]Quirino+2023.MNRASL.523.L86; [14]Ostberg+2023.AJ.165.Funding: This work was supported by Fundação para a Ciência e a Tecnologia (FCT) through the research grant 2023.05220.BD.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".