No Venus-like atmosphere on TRAPPIST-1 c: confirmation from 3D climate modelling
- 1University of Lisbon, Faculty of Sciences, Department of Physics, Campo Grande, 1749-016, Lisbon, Portugal (dfquirino@fc.ul.pt)
- 2Instituto de Astrofísica e Ciências do Espaço (IA), Universidade de Lisboa, OAL, Edifício Leste, Tapada da Ajuda, 1349-018 Lisbon, Portugal
- 3Instituto de Astrofísica de Andalucía (IAA – CSIC), Glorieta de la Astronomía, 18008 Granada, Spain
- 4Laboratoire de Météorologie Dynamique/IPSL, CNRS, Sorbonne Université, École Normale Supérieure, PSL Research University, École Polytechnique, 75005 Paris, France
- 5NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
- 6Integrated Space Science and Technology Institute, Department of Physics, American University, Washington DC 20016, USA
- 7NASA GSFC Sellers Exoplanet Environments Collaboration, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
- 8Trottier Space Institute, McGill University, 3550 University Street, Montréal, QC H3A 2A7, Canada
- 9Space Science Institute, 4765 Walnut St, Suite B, Boulder, CO 80301, USA
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.
How to cite: Quirino, D., Gilli, G., Turbet, M., Fauchez, T., Navarro, T., and Machado, P.: No Venus-like atmosphere on TRAPPIST-1 c: confirmation from 3D climate modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-801, https://doi.org/10.5194/egusphere-egu24-801, 2024.
