Abstract
The first James Webb Space Telescope/MIRI photometric observations of TRAPPIST-1 b allowed for the detection of the thermal emission of the planet at 15 μm, suggesting that the planet could be a bare rock with a zero albedo and no redistribution of heat. These observations at 15 μm were acquired as part of Guaranteed Time Observer time that included a twin programme at 12.8 μm to obtain measurements inside and outside the CO2 absorption band. Here we present five new occultations of TRAPPIST-1 b observed with MIRI in an additional photometric band at 12.8 μm. We perform a global fit of the ten eclipses and derive a planet-to-star flux ratio and 1σ error of 452 ± 86 ppm and 775 ± 90 ppm at 12.8 μm and 15 μm, respectively. We find that two main scenarios emerge. An airless planet model with an unweathered (fresh) ultramafic surface, that could be indicative of relatively recent geological processes, fits the data well. Alternatively, a thick, pure-CO2 atmosphere with photochemical hazes that create a temperature inversion and result in the CO2 feature being seen in emission also works, although with some caveats. Our results highlight the challenges in accurately determining a planet’s atmospheric or surface nature solely from broadband filter measurements of its emission, but also point towards two very interesting scenarios that will be further investigated with the forthcoming phase curve of TRAPPIST-1 b.
| Original language | English |
|---|---|
| Pages (from-to) | 358-369 |
| Number of pages | 12 |
| Journal | Nature Astronomy |
| Volume | 9 |
| Issue number | 3 |
| DOIs | |
| Publication status | Published - Mar 2025 |
Funding
We thank M. Turbet and F. Selsis for discussion regarding the modelling of a putative atmosphere of TRAPPIST-1 b and its likelihood. We thank B. Charnay for discussion regarding photochemical haze formation processes and comparison with Titan. We thank J. Ih for sharing their bare-surface models published in ref. and for useful discussion regarding the calculation of the Bond albedo. We thank O. Lim for sharing their transmission spectra of TRAPPIST-1 b obtained from the reduction and analysis of JWST/NIRISS data and published in their paper ref. . We thank E. Agol for his help on planetary flux estimation equations. Finally, we thank A. Iyer for providing the SPHINX stellar spectrum model extrapolated on TRAPPIST-1\u2019s parameters. This work is based on observations made with the NASA/ESA/CSA JWST. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with programme 1279. MIRI draws on the scientific and technical expertise of the following organizations: NASA Ames Research Center, USA; Airbus Defence and Space, UK; CEA-Irfu, Saclay, France; Centre Spatial de Li\u00E8ge, Belgium; Consejo Superior de Investigaciones Cient\u00EDficas, Spain; Carl Zeiss Optronics, Germany; Chalmers University of Technology, Sweden; Danish Space Research Institute, Denmark; Dublin Institute for Advanced Studies, Ireland; European Space Agency, The Netherlands; ETCA, Belgium; ETH Zurich, Switzerland; Goddard Space Flight Center, USA; Institut d\u2019Astrophysique Spatiale, France; Instituto Nacional de T\u00E9cnica Aeroespacial, Spain; Institute for Astronomy, Edinburgh, UK; Jet Propulsion Laboratory, USA; Laboratoire d\u2019Astrophysique de Marseille (LAM), France; Leiden University, The Netherlands; NOVA Opt-IR group at Dwingeloo, The Netherlands; Northrop Grumman, USA; Max-Planck-Institut f\u00FCr Astronomie (MPIA), Heidelberg, Germany; Laboratoire d\u2019Etudes Spatiales et d\u2019Instrumentation en Astrophysique (LESIA), France; Paul Scherrer Institut, Switzerland; Raytheon Vision Systems, USA; RUAG Aerospace, Switzerland; Rutherford Appleton Laboratory (RAL Space), UK; Space Telescope Science Institute, USA; Toegepast Natuurwetenschappelijk Onderzoek (TNO-TPD), The Netherlands; UK Astronomy Technology Centre, UK; University College London, UK; University of Amsterdam, The Netherlands; University of Arizona, USA; University of Bern, Switzerland; University of Cardiff, UK; University of Cologne, Germany; University of Ghent, Belgium; University of Groningen, The Netherlands; University of Leicester, UK; University of Leuven, Belgium; University of Stockholm, Sweden. The following national and international funding agencies funded and supported the MIRI development: NASA; European Space Agency (ESA); Belgian Science Policy Office (BELSPO); Centre Nationale d\u2019Etudes Spatiales (CNES); Danish National Space Centre; Deutsches Zentrum f\u00FCr Luft- und Raumfahrt (DLR); Enterprise Ireland; Ministerio De Economalia y Competividad; Netherlands Research School for Astronomy (NOVA); Netherlands Organisation for Scientific Research (NWO); Science and Technology Facilities Council; Swiss Space Office; Swedish National Space Agency; UK Space Agency. E.D. acknowledges support from the innovation and research Horizon 2020 programme in the context of the Marie Sklodowska-Curie subvention 945298 as well as from the Paris Observatory\u2013PSL fellowship. M. Gillon is FRS-FNRS Research Director. His contribution to this work was done in the framework of the PORTAL project funded by the Federal Public Planning Service Science Policy (BELSPO) within its BRAIN-be: Belgian Research Action through the Interdisciplinary Networks programme. P.-O.L., C.C., A.D., R.G. and A.C. acknowledge funding support from CNES. T.G. and T.J.B. acknowledge support from NASA in WBS 411672.07.04.01.02. O.A., I.A., B.V. and P.R. thank the ESA and BELSPO for their support in the framework of the PRODEX Programme. D.B. is supported by Spanish MCIN/AEI/10.13039/501100011033 grants PID2019-107061GB-C61 and MDM-2017-0737. L.D. acknowledges funding from the KU Leuven Interdisciplinary Grant (IDN/19/028), the European Union H2020-MSCA-ITN-2019 under grant 860470 (CHAMELEON) and the FWO research grant G086217N. J.P. acknowledges financial support from the UK Science and Technology Facilities Council and the UK Space Agency. G. Ostlin acknowledges support from the Swedish National Space Board and the Knut and Alice Wallenberg Foundation. P.T. acknowledges support by the European Research Council under grant agreement ATMO 757858. E.D. has received funding from the European Union\u2019s Horizon 2020 research and innovation programme under the Marie Sk\u0142odowska-Curie actions grant agreement 945298-ParisRegionFP as well as from the Paris Observatory\u2013PSL fellowship. L.C. acknowledges support by grant PIB2021-127718NB-100 from the Spanish Ministry of Science and Innovation/State Agency of Research MCIN/AEI/10.13039/501100011033. E.F.v.D. acknowledges support from A-ERC grant 101019751 MOLDISK. T.P.R. acknowledges support from the ERC 743029 EASY. G. Olofsson acknowledges support from SNSA. P.P. thanks the Swiss National Science Foundation (SNSF) for financial support under grant number 200020_200399. O.A. is a senior research associate of the Fonds de la Recherche Scientifique\u2014FNRS.
Austrian Fields of Science 2012
- 103003 Astronomy
- 103004 Astrophysics
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