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.
This is a preview of subscription content, access via your institution
Open Access articles citing this article.
Nature Open Access 19 June 2023
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 51 print issues and online access
$199.00 per year
only $3.90 per issue
Rent or buy this article
Prices vary by article type
Prices may be subject to local taxes which are calculated during checkout
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.
Gillon, M. et al. Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1. Nature 542, 456–460 (2017).
Ducrot, E. et al. The 0.8–4.5 μm broadband transmission spectra of TRAPPIST-1 planets. Astron. J. 156, 218 (2018).
de Wit, J. et al. Atmospheric reconnaissance of the habitable-zone Earth-sized planets orbiting TRAPPIST-1. Nat. Astron. 2, 214–219 (2018).
Zhang, Z., Zhou, Y., Rackham, B. V. & Apai, D. The near-infrared transmission spectra of TRAPPIST-1 planets b, c, d, e, f, and g and stellar contamination in multi-epoch transit spectra. Astron. J. 156, 178 (2018).
Garcia, L. J. et al. HST/WFC3 transmission spectroscopy of the cold rocky planet TRAPPIST-1h. Astron. Astrophys. 665, A19 (2022).
Burgasser, A. J. & Mamajek, E. E. On the age of the TRAPPIST-1 system. Astrophys. J. 845, 110 (2017).
Agol, E. et al. Refining the transit-timing and photometric analysis of TRAPPIST-1: masses, radii, densities, dynamics, and ephemerides. Planet Sci. J. 2, 1 (2021).
Liebert, J. & Gizis, J. E. RI photometry of 2MASS-selected late M and L dwarfs. Publ. Astron. Soc. Pac. 118, 659–670 (2006).
Roettenbacher, R. M. & Kane, S. R. The stellar activity of TRAPPIST-1 and consequences for the planetary atmospheres. Astrophys. J. 851, 77 (2017).
Paudel, R. R. et al. K2 ultracool dwarfs survey. III. White light flares are ubiquitous in M6-L0 dwarfs. Astrophys. J. 858, 55 (2018).
Baraffe, I., Chabrier, G., Allard, F. & Hauschildt, P. H. Evolutionary models for solar metallicity low-mass stars: mass-magnitude relationships and color-magnitude diagrams. Astron. Astrophys. 337, 403–412 (1998).
Luger, R. & Barnes, R. Extreme water loss and abiotic O2 buildup on planets throughout the habitable zones of M dwarfs. Astrobiology 15, 119–143 (2015).
Bolmont, E. et al. Water loss from terrestrial planets orbiting ultracool dwarfs: implications for the planets of TRAPPIST-1. Mon. Not. R. Astron. Soc. 464, 3728–3741 (2017).
Tarter, J. C. et al. A reappraisal of the habitability of planets around M dwarf stars. Astrobiology 7, 30–65 (2007).
Turbet, M. et al. Modeling climate diversity, tidal dynamics and the fate of volatiles on TRAPPIST-1 planets. Astron. Astrophys. 612, A86 (2018).
Tilley, M. A., Segura, A., Meadows, V., Hawley, S. & Davenport, J. Modeling repeated M dwarf flaring at an Earth-like planet in the habitable zone: atmospheric effects for an unmagnetized planet. Astrobiology 19, 64–86 (2019).
Airapetian, V. S. et al. Impact of space weather on climate and habitability of terrestrial-type exoplanets. Int. J. Astrobiol. 19, 136–194 (2020).
Grayver, A., Bower, D. J., Saur, J., Dorn, C. & Morris, B. M. Interior heating of rocky exoplanets from stellar flares with application to TRAPPIST-1. Astrophys. J. Lett. 941, L7 (2022).
Krissansen-Totton, J. & Fortney, J. J. Predictions for observable atmospheres of Trappist-1 planets from a fully coupled atmosphere–interior evolution model. Astrophys. J. 933, 115 (2022).
Lincowski, A. P. et al. Evolved climates and observational discriminants for the TRAPPIST-1 planetary system. Astrophys. J. 867, 76 (2018).
Turbet, M. et al. A review of possible planetary atmospheres in the TRAPPIST-1 system. Space Sci. Rev. 216, 100 (2020).
Barstow, J. K. & Irwin, P. G. J. Habitable worlds with JWST: transit spectroscopy of the TRAPPIST-1 system? Mon. Not. R. Astron. Soc. 461, L92–L96 (2016).
Lustig-Yaeger, J., Meadows, V. S. & Lincowski, A. P. The detectability and characterization of the TRAPPIST-1 exoplanet atmospheres with JWST. Astron. J. 158, 27 (2019).
Crossfield, I. J. M. Observations of exoplanet atmospheres. Publ. Astron. Soc. Pac. 127, 941 (2015).
Koll, D. D. B. A scaling for atmospheric heat redistribution on tidally locked rocky planets. Astrophys. J. 924, 134 (2022).
Koll, D. D. B. et al. Identifying candidate atmospheres on rocky M dwarf planets via eclipse photometry. Astrophys. J. 886, 140 (2019).
Mansfield, M. et al. Identifying atmospheres on rocky exoplanets through inferred high albedo. Astrophys. J. 886, 141 (2019).
Ducrot, E. et al. TRAPPIST-1: global results of the Spitzer exploration science program Red Worlds. Astron. Astrophys. 640, A112 (2020).
Rieke, G. H. et al. The mid-infrared instrument for the James Webb Space Telescope, I: introduction. Publ. Astron. Soc. Pac. 127, 584 (2015).
Bell, T. et al. Eureka!: an end-to-end pipeline for JWST time-series observations. J. Open Source Softw. 7, 4503 (2022).
Husser, T. O. et al. A new extensive library of PHOENIX stellar atmospheres and synthetic spectra. Astron. Astrophys. 553, A6 (2013).
Cowan, N. B. & Agol, E. A model for thermal phase variations of circular and eccentric exoplanets. Astrophys. J. 726, 82 (2011).
University of Washington. VPL Spectral Explorer (2018); https://live-vpl-test.pantheonsite.io/models/vpl-spectral-explorer/.
Delrez, L. et al. Early 2017 observations of TRAPPIST-1 with Spitzer. Mon. Not. R. Astron. Soc. 475, 3577–3597 (2018).
Kreidberg, L. et al. Absence of a thick atmosphere on the terrestrial exoplanet LHS 3844b. Nature 573, 87–90 (2019).
Lightsey, P. A. & Wei, Z. James Webb Space Telescope stray light performance status update. In Proc. SPIE 8442, Space Telescopes and Instrumentation 2012: Optical, Infrared, and Millimeter Wave 84423B (SPIE, 2012).
Rigby, J. R. et al. How dark the sky: the JWST backgrounds. Publ. Astron. Soc. Pac. 135, 048002 (2023).
JWST Calibration Pipeline Developers. JWST: Python library for science observations from the James Webb Space Telescope. GitHub https://github.com/spacetelescope/jwst (2022).
CRDS Developers. CRDS: calibration reference data system for HST and JWST. GitHub https://github.com/spacetelescope/crds (2022).
Rigby, J. et al. The science performance of JWST as characterized in commissioning. Publ. Astron. Soc. Pac. 135, 048001 (2023).
Guillard, P. et al. MIRI point spread functions: radial and encircled energy profiles (2023); https://jwst-docs.stsci.edu/jwst-mid-infrared-instrument/miri-performance/miri-point-spread-functions#MIRIPointSpreadFunctions-Radialandencircledenergyprofiles.
Luger, R. et al. rodluger/starry: v1.2.0. Zenodo https://zenodo.org/record/5567790/export/csl (2021).
Salvatier, J., Wiecki, T. V. & Fonnesbeck, C. Probabilistic programming in Python using PyMC3. PeerJ Comput. Sci. 2, e55 (2016).
Gelman, A. & Rubin, D. B. Inference from iterative simulation using multiple sequences. Stat. Sci. 7, 457–472 (1992).
Allan, D. W. Statistics of atomic frequency standards. IEEE Proc. 54, 221–230 (1966).
Gillon, M. et al. The Spitzer search for the transits of HARPS low-mass planets. Astron. Astrophys. 518, A25 (2010).
Gillon, M. et al. The TRAPPIST survey of southern transiting planets. I. Thirty eclipses of the ultra-short period planet WASP-43 b. Astron. Astrophys. 542, A4 (2012).
Gillon, M. et al. Search for a habitable terrestrial planet transiting the nearby red dwarf GJ 1214. Astron. Astrophys. 563, A21 (2014).
Mandel, K. & Agol, E. Analytic light curves for planetary transit searches. Astrophys. J. Lett. 580, L171–L175 (2002).
Bouwman, J. et al. Spectroscopic time series performance of the mid-infrared instrument on the JWST. Publ. Astron. Soc. Pac. 135, 038002 (2023).
Foreman-Mackey, D., Hogg, D. W., Lang, D. & Goodman, J. emcee: the MCMC hammer. Publ. Astron. Soc. Pac. 125, 306 (2013).
Lim, P. L., Diaz, R. I. & Laidler, V. PySynphot user’s guide (2015); https://pysynphot.readthedocs.io/en/latest/.
Harris, C. R. et al. Array programming with NumPy. Nature 585, 357–362 (2020).
The Astropy Collaboration. The Astropy project: sustaining and growing a community-oriented open-source project and the latest major release (v5.0) of the core package. Astrophys. J. 935, 167 (2022).
Hunter, J. D. Matplotlib: a 2D graphics environment. Comput. Sci. Eng. 9, 90–95 (2007).
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.
The authors declare no competing interests.
Peer review information
Nature thanks L. Kreidberg and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
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.
About this article
Cite this article
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
This article is cited by
Nature Astronomy (2023)