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Thermal emission from the Earth-sized exoplanet TRAPPIST-1 b using JWST

Nature volume 618, pages 39–42 (2023)Cite this article

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Abstract

The TRAPPIST-1 system is remarkable for its seven planets that are similar in size, mass, density and stellar heating to the rocky planets Venus, Earth and Mars in the Solar System1. All the TRAPPIST-1 planets have been observed with transmission spectroscopy using the Hubble or Spitzer space telescopes, but no atmospheric features have been detected or strongly constrained2,3,4,5. TRAPPIST-1 b is the closest planet to the M-dwarf star of the system, and it receives four times as much radiation as Earth receives from the Sun. This relatively large amount of stellar heating suggests that its thermal emission may be measurable. Here we present photometric secondary eclipse observations of the Earth-sized exoplanet TRAPPIST-1 b using the F1500W filter of the mid-infrared instrument on the James Webb Space Telescope (JWST). We detect the secondary eclipses in five separate observations with 8.7σ confidence when all data are combined. These measurements are most consistent with re-radiation of the incident flux of the TRAPPIST-1 star from only the dayside hemisphere of the planet. The most straightforward interpretation is that there is little or no planetary atmosphere redistributing radiation from the host star and also no detectable atmospheric absorption of carbon dioxide (CO2) or other species.

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Fig. 1: Combined TRAPPIST-1 b MIRI F1500W secondary eclipse light curve.
Fig. 2: TRAPPIST-1 b F1500W measured flux and spectral models.

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Data availability

The data used in this paper are associated with the JWST-GTO-1177 programme (observations 7–11) and will be publicly available from the Mikulski Archive for Space Telescopes (https://mast.stsci.edu) at the end of their one-year exclusive-access periods. Source data are provided with this paper.

Code availability

We used the following codes to process, extract, reduce and analyse the data: STScI JWST calibration pipeline38; Eureka!30; emcee51; starry42; PyMC3 (ref. 43); PySynphot52; and the standard Python libraries numpy53, astropy54 and matplotlib55. These were incorporated into custom Python notebooks for data analysis. These notebooks are available from the corresponding author on request. The notebooks were developed by a NASA employee and cannot be posted publicly until approved by NASA.

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Acknowledgements

We thank E. Schlawin, M. Gillon, V. Parmentier and E. Rauscher for discussions and L. Kreidberg for comments that helped to improve the manuscript. 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 under NASA contract NAS 5-03127 for JWST. These observations are associated with the JWST-GTO-1177 programme. We thank the MIRI instrument team and the many other people who contributed to the success of JWST. T.P.G. and T.J.B. acknowledge funding support from the NASA Next Generation Space Telescope Flight Investigations programme (now JWST) by WBS 411672.07.04.01.02. This material is based on work supported by NASA Interdisciplinary Consortia for Astrobiology Research (NNH19ZDA001N-ICAR) under award number 19-ICAR19_2-0041 (to J.J.F.) and NASA WBS 811073.02.12.04.71 (to T.P.G.). P.-O.L. acknowledges funding support from CNES. E.D. acknowledges support from the EU Horizon 2020 research and innovation programme in the context of the Marie Skłodowska-Curie subvention 945298. E.D. is a Paris Region Fellow and is funded by the Marie Skłodowska-Curie Actions.

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Authors and Affiliations

  1. Space Science and Astrobiology Division, NASA Ames Research Center, Moffett Field, CA, USA

    Thomas P. Greene & Taylor J. Bell

  2. Bay Area Environmental Research Institute, NASA Ames Research Center, Moffett Field, CA, USA

    Taylor J. Bell

  3. Université Paris-Saclay, Université Paris-Cité, CEA, CNRS, Gif-sur-Yvette, France

    Elsa Ducrot, Achrène Dyrek & Pierre-Olivier Lagage

  4. Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA

    Jonathan J. Fortney

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Contributions

T.P.G. provided the programme leadership, devised the observational programme, led setting the observation parameters, contributed to the data analysis, led the interpretation of the results and led the writing of the manuscript. T.J.B. verified the observing parameters and led the data analysis. E.D. checked and contributed to the observing parameters, data analysis and interpretation of the results. A.D. contributed to the data reduction. P.-O.L. contributed to the design of the observational programme and setting the observing parameters, commented on the draft manuscript and contributed to the data analysis. J.J.F. contributed to the design of the observational programme, provided information for the paper and helped to interpret the results.

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Correspondence to Thomas P. Greene.

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Extended data figures and tables

Extended Data Fig. 1 Light curves of individual observations and the Joint Fit #1 models.

a. The raw light curves from each of our five visits normalized by their median value are shown in color, while the fitted model from Joint Fit #1 including systematic noise is shown using a black line. The date in UT of each visit is indicated by the y-axis labels. Each visit did not start at the same orbital phase, so the apparent movement in the eclipse time is simply caused by when the observations began. b. The same data and model from each visit after the removal of systematic noise. Overplotted are data binned at a cadence of 9.7 minutes (14 integrations) to more clearly visualize the detection of the eclipse in each visit. All error bars show 1σ uncertainties in both panels.

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Extended Data Table 1 Mid-eclipse times
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Greene, T.P., Bell, T.J., Ducrot, E. et al. Thermal emission from the Earth-sized exoplanet TRAPPIST-1 b using JWST. Nature 618, 39–42 (2023). https://doi.org/10.1038/s41586-023-05951-7

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