One aim of modern astronomy is to detect temperate, Earth-like exoplanets that are well suited for atmospheric characterization. Recently, three Earth-sized planets were detected that transit (that is, pass in front of) a star with a mass just eight per cent that of the Sun, located 12 parsecs away1. The transiting configuration of these planets, combined with the Jupiter-like size of their host star—named TRAPPIST-1—makes possible in-depth studies of their atmospheric properties with present-day and future astronomical facilities1,2,3. Here we report the results of a photometric monitoring campaign of that star from the ground and space. Our observations reveal that at least seven planets with sizes and masses similar to those of Earth revolve around TRAPPIST-1. The six inner planets form a near-resonant chain, such that their orbital periods (1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small integers. This architecture suggests that the planets formed farther from the star and migrated inwards4,5. Moreover, the seven planets have equilibrium temperatures low enough to make possible the presence of liquid water on their surfaces6,7,8.
This is a preview of subscription content, access via your institution
Open Access articles citing this article.
Space Science Reviews Open Access 13 May 2022
Nature Astronomy Open Access 13 January 2022
Subscribe to Nature+
Get immediate online access to the entire Nature family of 50+ journals
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Gillon, M. et al. Temperate Earth-sized planets transiting a nearby ultracool dwarf star. Nature 533, 221–224 (2016)
de Wit, J. et al. A combined transmission spectrum of the Earth-sized exoplanets TRAPPIST-1 b and c. Nature 537, 69–72 (2016)
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)
Cresswell, P. & Nelson, R. P. On the evolution of multiple protoplanets embedded in a protostellar disc. Astron. Astrophys. 450, 833–853 (2006)
Mills, S. M. et al. A resonant chain of four transiting, sub-Neptune planets. Nature 533, 509–512 (2016)
Kopparapu, R. K. et al. Habitable zones around main-sequence stars: new estimates. Astrophys. J. 765, 131 (2013)
Leconte, J. et al. 3D climate modelling of close-in land planets: circulation patterns, climate moist instability, and habitability. Astron. Astrophys. 554, A69 (2013)
Stevenson, D. J. Life-sustaining planets in interstellar space? Nature 400, 32 (1999)
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)
Agol, E., Steffen, J., Sari, R. & Clarkson, W. On detecting terrestrial planets with timing of giant planet transits. Mon. Not. R. Astron. Soc. 359, 567–579 (2005)
Holman, M. J. & Murray, N. W. The use of transit timing to detect terrestrial-mass extrasolar planets. Science 307, 1288–1291 (2005)
Fabrycky, D. C. in Exoplanets (ed. Seager, S. ) 217–238 (Univ. Arizona Press, 2010)
Winn, J. N. in Exoplanets (ed. Seager, S. ) 55–77 (Univ. Arizona Press, 2010)
Zeng, L., Sasselov, D. D. & Jacobsen, S. B. Mass-radius relation for rocky planets based on PREM. Astrophys. J. 819, 127 (2016)
Chiang, E. & Laughlin, G. The minimum-mass extrasolar nebula: in situ formation of close-in super-Earths. Mon. Not. R. Astron. Soc. 431, 3444–3455 (2013)
Kane, S. R., Hinkel, N. R. & Raymond, S. N. Solar system moons as analogs for compact exoplanetary systems. Astron. J. 146, 122 (2013)
MacDonald, M. G. et al. A dynamical analysis of the Kepler-80 system of five transiting planets. Astron. J. 152, 105 (2016)
Papaloizou, J. C. B. & Szuszkiewicz, E. On the migration-induced resonances in a system of two planets with masses in the Earth mass range. Mon. Not. R. Astron. Soc. 363, 153–176 (2005)
Terquem, C. & Papaloizou, J. C. B. Migration and the formation of systems of hot super-Earths and Neptunes. Astrophys. J. 654, 1110–1120 (2007)
Goldreich, P. & Tremaine, S. Disk-satellite interactions. Astrophys. J. 241, 425–441 (1980)
Raymond, S. N., Barnes, R. & Mandell, A. M. Observable consequences of planet formation models in systems with close-in terrestrial planets. Mon. Not. R. Astron. Soc. 384, 663–674 (2008)
Alibert, Y. & Benz, W. Formation and composition of planets around very low mass stars. Astron. Astrophys. 598, L5 (2017)
Kasting, J. F., Whitmire, D. P. & Reynolds, R. T. Habitable zones around main-sequence stars. Icarus 101, 108–128 (1993)
Ribas, I. et al. The habitability of Proxima Centauri b. I. Irradiation, rotation and volatile inventory from formation to the present. Astron. Astrophys. 596, A111 (2016)
Wordsworth, R. D. et al. Is Gliese 581d habitable? Some constraints from radiative-convective climate modeling. Astron. Astrophys. 522, A22 (2010)
Turbet, M. et al. The habitability of Proxima Centauri b II. Possible climates and observability. Astron. Astrophys. 596, A112 (2016)
Kopparapu, R. K. et al. The inner edge of the habitable zone for synchronously rotating planets around low-mass stars using general circulation models. Astrophys. J. 819, 84 (2016)
Bolmont, E. et al. Water loss from Earth-sized planets in the habitable zones of ultracool dwarfs: implications for the planets of TRAPPIST-1. Mon. Not. R. Astron. Soc. 464, 3728–3741 (2017)
Barnes, R. et al. Tidal limits to planetary habitability. Astrophys. J. 700, L30–L33 (2009)
Luger, R. & Barnes, R. Extreme water loss and abiotic O2 buildup on planets throughout the habitable zone of M dwarfs. Astrobiol. 15, 119–143 (2015)
Gillon, M. et al. TRAPPIST: a robotic telescope dedicated to the study of planetary systems. EPJ Web Conf. 11, 06002 (2011)
Jehin, E. et al. TRAPPIST: TRAnsiting Planets and PlanetesImals Small Telescope. Messenger 145, 2–6 (2011)
Pirard, J.-F. et al. HAWK-I: a new wide-field 1- to 2.5 μm imager for the VLT. Proc. SPIE 5492, 1763–1772 (2004)
Casali, M. et al. The UKIRT IR Wide-Field Camera (WFCAM). In The New Era of Wide-Field Astronomy (eds Clowes, R., Adamson, A. & Bromage, G. ) 357–363 (ASPC Conf. Series Vol. 232, 2001)
Benn, C., Dee, K. & Agócs, T. ACAM: a new imager/spectrograph for the William Herschel Telescope. Proc. SPIE 7014, 70146X (2008)
Stetson, P. B. DAOPHOT—a computer program for crowded-field stellar photometry. Publ. Astron. Soc. Pacif. 99, 191–222 (1987)
Fazio, G. G. et al. The Infrared Array Camera (IRAC) for the Spitzer Space Telescope. Astrophys. J. Suppl. Ser. 154, 10–17 (2004)
Ingalls, J. G. et al. Intra-pixel gain variations and high-precision photometry with the Infrared Array Camera (IRAC). Proc. SPIE 8442, http://dx.doi.org/10.1117/12.926947 (2012)
Knutson, H. A. et al. The 3.6–8.0 μm broadband emission spectrum of HD 209458b: evidence for an atmospheric temperature inversion. Astrophys. J. 673, 526–531 (2008)
Gillon, M. et al. Search for a habitable terrestrial planet transiting the nearby red dwarf GJ 1214. Astron. Astrophys. 563, A21 (2014)
Eastman, J., Siverd, R. & Gaudi, B. S. Achieving better than 1 minute accuracy in the heliocentric and barycentric Julian dates. Publ. Astron. Soc. Pacif. 122, 935–946 (2010)
Mandel, K. & Agol, E. Analytic light curves for planetary transit searches. Astrophys. J. 580, L171–L175 (2002)
Schwarz, G. E. Estimating the dimension of a model. Ann. Stat. 6, 461–464 (1978)
Filippazzo, J. C. et al. Fundamental parameters and spectral energy distributions of young and field age objects with masses spanning the stellar to planetary regime. Astrophys. J. 810, 158 (2015)
Claret, A. A new non-linear limb-darkening law for LTE stellar atmosphere models. Calculations for −5.0 ≤ log[M/H] ≤ +1, 2000K ≤ Teff ≤ 50000K at several surface gravities. Astron. Astrophys. 363, 1081–1190 (2000)
Claret, A. & Bloemen, S. Gravity and limb-darkening coefficients for the Kepler, CoRoT, Spitzer, uvby, UBVRIJHK, and Sloan photometric systems. Astron. Astrophys. 529, A75 (2011)
Gelman, A. & Rubin., D. B. Inference from iterative simulation using multiple sequences. Stat. Sci. 7, 457–472 (1992)
Deck, K. M. et al. TTVFast: an efficient and accurate code for transit timing inversion problems. Astrophys. J. 787, 132 (2014)
Chambers, J. E. A hybrid symplectic integrator that permits close encounters between massive bodies. Mon. Not. R. Astron. Soc. 304, 793–799 (1999)
Agol, E. & Deck, K. M. Transit timing to first order in eccentricity. Astrophys. J. 818, 177 (2016)
Deck, K. M. & Agol, E. Transit timing variations for planets near eccentricity-type mean motion resonances. Astrophys. J. 821, 96 (2016)
Levenberg, K. A method for certain problems in least squares. Q. Appl. Math. 2, 164–168 (1944)
Nelder, J. A. & Mead, R. A simplex method for function minimization. Comput. J. 7, 308–313 (1965)
Hanno, R. & Tamayo, D. WHFast: a fast and unbiased implementation of a symplectic Wisdom-Holman integrator for long-term gravitational simulations. Mon. Not. R. Astron. Soc. 452, 376–388 (2015)
Pu, B. & Wu, Y. Spacing of Kepler planets: sculpting by dynamical instability. Astrophys. J. 807, 44 (2015); erratum 819, 170 (2016)
Bolmont, E. et al. Formation, tidal evolution, and habitability of the Kepler-186 system. Astrophys. J. 793, 3 (2014)
Bolmont, E. et al. Mercury-T: a new code to study tidally evolving multi-planet systems. Applications to Kepler-62. Astron. Astrophys. 583, A116 (2015)
Deck, K. M., Payne, M. & Holman, M. J. First-order resonance overlap and the stability of close two-planet systems. Astrophys. J. 774, 129 (2013)
This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. The material presented here is based on work supported in part by NASA under contract no. NNX15AI75G. TRAPPIST-South is a project funded by the Belgian Fonds (National) de la Recherche Scientifique (F.R.S.-FNRS) under grant FRFC 2.5.594.09.F, with the participation of the Swiss National Science Foundation (FNS/SNSF). TRAPPIST-North is a project funded by the University of Liège, and performed in collaboration with Cadi Ayyad University of Marrakesh. The research leading to these results has received funding from the European Research Council (ERC) under the FP/2007-2013 ERC grant agreement no. 336480, and under the H2020 ERC grant agreement no. 679030; and from an Actions de Recherche Concertée (ARC) grant, financed by the Wallonia–Brussels Federation. The VLT data used in this work were taken under program 296.C-5010(A). UKIRT is supported by NASA and operated under an agreement among the University of Hawaii, the University of Arizona, and Lockheed Martin Advanced Technology Center; operations are enabled through the cooperation of the East Asian Observatory. The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University (JMU) in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, with financial support from the UK Science and Technology Facilities Council. This paper uses observations made at the South African Astronomical Observatory (SAAO). M.G., E.J. and V.V.G. are F.R.S.-FNRS research associates. B.-O.D. acknowledges support from the Swiss National Science Foundation in the form of a SNSF Professorship (PP00P2_163967). E.A. acknowledges support from National Science Foundation (NSF) grant AST-1615315, and NASA grants NNX13AF62G and NNH05ZDA001C. E.B. acknowledges that this work is part of the F.R.S.-FNRS ExtraOrDynHa research project and acknowledges funding by the European Research Council through ERC grant SPIRE 647383. S.N.R. thanks the Agence Nationale pour la Recherche (ANR) for support via grant ANR-13-BS05-0003-002 (project MOJO). D.L.H. acknowledges financial support from the UK Science and Technology Facilities Council. The authors thank C. Owen, C. Wolf and the rest of the SkyMapper team for their attempts to monitor the star from Australia; from UKIRT, the director R. Green and the staff scientists W. Varricatt and T. Kerr; the ESO staff at Paranal for their support with the HAWK-I observations; JMU and their flexibility as regards the Liverpool Telescope schedule, which allowed us to search actively for the planets, and to extend our time allocation in the face of amazing results; for the William Herschel Telescope, C. Fariña, F. Riddick, F. Jímenez and O. Vaduvescu for their help and kindness during observations; and for SAAO, the telescopes operations manager R. Sefako for his support.
The authors declare no competing financial interests.
Reviewer Information Nature thanks D. Deming and I. Snellen for their contribution to the peer review of this work.
Extended data figures and tables
The black points show the differential photometric measurements extracted from VLT/HAWK-I images taken on 11 December 2015, with the formal 1σ errors shown as vertical lines. The best-fit triple-transit model is shown as a red line. Possible configurations of the planets relative to the stellar disc are shown below the light curve for three different times (red, planet c; yellow, planet e; green, planet f). The relative positions and sizes of the planets, as well as the impact parameters, correspond to the values in Table 1.
The black points show the photometric measurements, binned per 0.005 days (7.2 min). The error for each bin (shown as a vertical line) was computed as the 1σ error on the average. These light curves are divided by their best-fit instrumental models and by the best-fit transit models of other planets (for multiple transits). The best-fit transit models are shown as solid lines. The light curves are period-folded on the best-fit transit ephemeris given in Table 1, their relative shifts on the x-axis reflecting TTVs due to planet–planet interactions (see text). The epoch of the transit and the facility used to observe it are indicated above each light curve.
About this article
Cite this article
Gillon, M., Triaud, A., Demory, BO. et al. Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1. Nature 542, 456–460 (2017). https://doi.org/10.1038/nature21360
Nature Astronomy (2022)
Nature Astronomy (2022)
Nature Astronomy (2022)
Understanding planetary context to enable life detection on exoplanets and test the Copernican principle
Nature Astronomy (2022)
Space Science Reviews (2022)