Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1

Abstract

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.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Figure 1: The TRAPPIST-1 system as seen by Spitzer.
Figure 2: Mass–radius and incident-flux–radius diagrams for terrestrial planets.

References

  1. 1

    Gillon, M. et al. Temperate Earth-sized planets transiting a nearby ultracool dwarf star. Nature 533, 221–224 (2016)

    ADS  CAS  Article  PubMed  Google Scholar 

  2. 2

    de Wit, J. et al. A combined transmission spectrum of the Earth-sized exoplanets TRAPPIST-1 b and c. Nature 537, 69–72 (2016)

    ADS  CAS  Article  Google Scholar 

  3. 3

    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)

    ADS  CAS  Article  Google Scholar 

  4. 4

    Cresswell, P. & Nelson, R. P. On the evolution of multiple protoplanets embedded in a protostellar disc. Astron. Astrophys. 450, 833–853 (2006)

    ADS  Article  Google Scholar 

  5. 5

    Mills, S. M. et al. A resonant chain of four transiting, sub-Neptune planets. Nature 533, 509–512 (2016)

    ADS  CAS  Article  PubMed  Google Scholar 

  6. 6

    Kopparapu, R. K. et al. Habitable zones around main-sequence stars: new estimates. Astrophys. J. 765, 131 (2013)

    ADS  Article  Google Scholar 

  7. 7

    Leconte, J. et al. 3D climate modelling of close-in land planets: circulation patterns, climate moist instability, and habitability. Astron. Astrophys. 554, A69 (2013)

    Article  Google Scholar 

  8. 8

    Stevenson, D. J. Life-sustaining planets in interstellar space? Nature 400, 32 (1999)

    ADS  CAS  Article  PubMed  Google Scholar 

  9. 9

    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)

    ADS  Article  Google Scholar 

  10. 10

    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)

    ADS  Article  Google Scholar 

  11. 11

    Holman, M. J. & Murray, N. W. The use of transit timing to detect terrestrial-mass extrasolar planets. Science 307, 1288–1291 (2005)

    ADS  CAS  Article  PubMed  Google Scholar 

  12. 12

    Fabrycky, D. C. in Exoplanets (ed. Seager, S. ) 217–238 (Univ. Arizona Press, 2010)

  13. 13

    Winn, J. N. in Exoplanets (ed. Seager, S. ) 55–77 (Univ. Arizona Press, 2010)

  14. 14

    Zeng, L., Sasselov, D. D. & Jacobsen, S. B. Mass-radius relation for rocky planets based on PREM. Astrophys. J. 819, 127 (2016)

    ADS  Article  Google Scholar 

  15. 15

    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)

    ADS  Article  Google Scholar 

  16. 16

    Kane, S. R., Hinkel, N. R. & Raymond, S. N. Solar system moons as analogs for compact exoplanetary systems. Astron. J. 146, 122 (2013)

    ADS  Article  Google Scholar 

  17. 17

    MacDonald, M. G. et al. A dynamical analysis of the Kepler-80 system of five transiting planets. Astron. J. 152, 105 (2016)

    ADS  Article  Google Scholar 

  18. 18

    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)

    ADS  Article  Google Scholar 

  19. 19

    Terquem, C. & Papaloizou, J. C. B. Migration and the formation of systems of hot super-Earths and Neptunes. Astrophys. J. 654, 1110–1120 (2007)

    ADS  Article  Google Scholar 

  20. 20

    Goldreich, P. & Tremaine, S. Disk-satellite interactions. Astrophys. J. 241, 425–441 (1980)

    ADS  MathSciNet  Article  Google Scholar 

  21. 21

    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)

    ADS  Article  Google Scholar 

  22. 22

    Alibert, Y. & Benz, W. Formation and composition of planets around very low mass stars. Astron. Astrophys. 598, L5 (2017)

  23. 23

    Kasting, J. F., Whitmire, D. P. & Reynolds, R. T. Habitable zones around main-sequence stars. Icarus 101, 108–128 (1993)

    ADS  CAS  Article  PubMed  Google Scholar 

  24. 24

    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)

    Article  Google Scholar 

  25. 25

    Wordsworth, R. D. et al. Is Gliese 581d habitable? Some constraints from radiative-convective climate modeling. Astron. Astrophys. 522, A22 (2010)

    Article  Google Scholar 

  26. 26

    Turbet, M. et al. The habitability of Proxima Centauri b II. Possible climates and observability. Astron. Astrophys. 596, A112 (2016)

    Article  Google Scholar 

  27. 27

    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)

    ADS  Article  Google Scholar 

  28. 28

    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)

    ADS  CAS  Article  Google Scholar 

  29. 29

    Barnes, R. et al. Tidal limits to planetary habitability. Astrophys. J. 700, L30–L33 (2009)

    ADS  CAS  Article  Google Scholar 

  30. 30

    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)

    ADS  CAS  Article  Google Scholar 

  31. 31

    Gillon, M. et al. TRAPPIST: a robotic telescope dedicated to the study of planetary systems. EPJ Web Conf. 11, 06002 (2011)

    Article  Google Scholar 

  32. 32

    Jehin, E. et al. TRAPPIST: TRAnsiting Planets and PlanetesImals Small Telescope. Messenger 145, 2–6 (2011)

    ADS  Google Scholar 

  33. 33

    http://www.orca.ulg.ac.be/TRAPPIST/Trappist_main/Home.html

  34. 34

    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)

    ADS  Article  Google Scholar 

  35. 35

    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)

    Google Scholar 

  36. 36

    Benn, C., Dee, K. & Agócs, T. ACAM: a new imager/spectrograph for the William Herschel Telescope. Proc. SPIE 7014, 70146X (2008)

    ADS  Article  Google Scholar 

  37. 37

    http://telescope.livjm.ac.uk/TelInst/Inst/IOO/

  38. 38

    http://shoc.saao.ac.za/Documents/ShocnHelpful.pdf

  39. 39

    Stetson, P. B. DAOPHOT—a computer program for crowded-field stellar photometry. Publ. Astron. Soc. Pacif. 99, 191–222 (1987)

    ADS  Article  Google Scholar 

  40. 40

    Fazio, G. G. et al. The Infrared Array Camera (IRAC) for the Spitzer Space Telescope. Astrophys. J. Suppl. Ser. 154, 10–17 (2004)

    ADS  Article  Google Scholar 

  41. 41

    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)

  42. 42

    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)

    ADS  CAS  Article  Google Scholar 

  43. 43

    Gillon, M. et al. Search for a habitable terrestrial planet transiting the nearby red dwarf GJ 1214. Astron. Astrophys. 563, A21 (2014)

    Article  Google Scholar 

  44. 44

    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)

    ADS  Article  Google Scholar 

  45. 45

    Mandel, K. & Agol, E. Analytic light curves for planetary transit searches. Astrophys. J. 580, L171–L175 (2002)

    ADS  Article  Google Scholar 

  46. 46

    Schwarz, G. E. Estimating the dimension of a model. Ann. Stat. 6, 461–464 (1978)

    MathSciNet  Article  Google Scholar 

  47. 47

    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)

    ADS  Article  Google Scholar 

  48. 48

    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)

    ADS  CAS  Google Scholar 

  49. 49

    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)

    ADS  Article  Google Scholar 

  50. 50

    Gelman, A. & Rubin., D. B. Inference from iterative simulation using multiple sequences. Stat. Sci. 7, 457–472 (1992)

    Article  Google Scholar 

  51. 51

    Deck, K. M. et al. TTVFast: an efficient and accurate code for transit timing inversion problems. Astrophys. J. 787, 132 (2014)

    ADS  Article  Google Scholar 

  52. 52

    Chambers, J. E. A hybrid symplectic integrator that permits close encounters between massive bodies. Mon. Not. R. Astron. Soc. 304, 793–799 (1999)

    ADS  Article  Google Scholar 

  53. 53

    Agol, E. & Deck, K. M. Transit timing to first order in eccentricity. Astrophys. J. 818, 177 (2016)

    ADS  Article  Google Scholar 

  54. 54

    Deck, K. M. & Agol, E. Transit timing variations for planets near eccentricity-type mean motion resonances. Astrophys. J. 821, 96 (2016)

    ADS  Article  Google Scholar 

  55. 55

    Levenberg, K. A method for certain problems in least squares. Q. Appl. Math. 2, 164–168 (1944)

    MathSciNet  Article  Google Scholar 

  56. 56

    Nelder, J. A. & Mead, R. A simplex method for function minimization. Comput. J. 7, 308–313 (1965)

    MathSciNet  Article  Google Scholar 

  57. 57

    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)

    ADS  Article  Google Scholar 

  58. 58

    Pu, B. & Wu, Y. Spacing of Kepler planets: sculpting by dynamical instability. Astrophys. J. 807, 44 (2015); erratum 819, 170 (2016)

    ADS  Article  Google Scholar 

  59. 59

    Bolmont, E. et al. Formation, tidal evolution, and habitability of the Kepler-186 system. Astrophys. J. 793, 3 (2014)

    ADS  Article  Google Scholar 

  60. 60

    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)

    Article  Google Scholar 

  61. 61

    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)

    ADS  Article  Google Scholar 

Download references

Acknowledgements

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.

Author information

Affiliations

Authors

Contributions

M.G. leads the ultracool dwarf transit survey that uses the TRAPPIST telescope and led the photometric follow-up of the star TRAPPIST-1; he also planned and analysed most of the observations, led their scientific exploitation, and wrote most of the manuscript. A.H.M.J.T. led the observational campaign using the La Palma telescopes (the Liverpool Telescope, LT, and William Herschel Telescope, WHT). C.M.C. managed the scheduling of the LT observations, and Ar.B. performed the photometric analysis of the resulting LT and WHT images. B.-O.D. led the TTV/dynamical simulations. E.A. and K.M.D. performed independent analyses of the transit timings. J.G.I. and S.J.C. helped to optimize the Spitzer observations. B.-O.D., J.G.I. and J.d.W. performed independent analyses of the Spitzer data. M.G., E.J., L.D., Ar.B., P.M., K.B., Y.A. and Z.B. performed the TRAPPIST observations and their analysis. S.M.L. obtained the director’s discretionary time on UKIRT, and, with E.J., managed the preparation of the UKIRT observations. M.T., J.L., F.S., E.B. and S.N.R. carried out atmospheric modelling for the planets and worked on the theoretical interpretation of their properties. V.V.G. managed the SAAO observations performed by C.S.F., M.R.B., D.L.H., A.C. and E.J.K. All co-authors assisted with writing the manuscript. A.H.M.J.T. prepared most of the figures.

Corresponding author

Correspondence to Michaël Gillon.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Additional information

Reviewer Information Nature thanks D. Deming and I. Snellen for their contribution to the peer review of this work.

Extended data figures and tables

Extended Data Figure 1 Light curve of a triple transit of planets c, e and f.

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. Source data

Extended Data Figure 2 Transit light curve for planets d and e.

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. Source data

Extended Data Figure 3 Transit light curves for planets f and g.

As for Extended Data Fig. 2, but for planets f and g. Source data

Extended Data Figure 4 TTVs measured for planets b, c, d, e, f and g.

For each planet, the best-fit TTV model computed with the n-body numerical integration code Mercury52 is shown as a red line. The 1 σ errors of the transit timing measurements are shown as vertical lines. Source data

Extended Data Table 1 Summary of the observation set used

PowerPoint slides

Source data

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

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

Download citation

Further reading

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing