Abstract
Located at the bottom of the main sequence, ultracool dwarf stars are widespread in the solar neighbourhood. Nevertheless, their extremely low luminosity has left their planetary population largely unexplored, and only one of them, TRAPPIST-1, has so far been found to host a transiting planetary system. In this context, we present the SPECULOOS project’s detection of an Earth-sized planet in a 17 h orbit around an ultracool dwarf of M6.5 spectral type located 16.8 pc away. The planet’s high irradiation (16 times that of Earth) combined with the infrared luminosity and Jupiter-like size of its host star make it one of the most promising rocky exoplanet targets for detailed emission spectroscopy characterization with JWST. Indeed, our sensitivity study shows that just ten secondary eclipse observations with the Mid-InfraRed Instrument/Low-Resolution Spectrometer on board JWST should provide strong constraints on its atmospheric composition and/or surface mineralogy.
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Data availability
All the data (Kast, SpeX and CARMENES spectra; SPECULOOS, Saint-EX, T150, MuSCAT3, GTC/HiPERCAM, UKIRT/WFCAM and TESS light curves) used in this work are publicly available via Zenodo at https://doi.org/10.5281/zenodo.10821723 (ref. 115). Source data are provided with this paper.
Code availability
The PROSE code used to reduce the SPECULOOS, TRAPPIST, and MuSCAT3 data is available at https://github.com/lgrcia/prose. The TRAFIT code used to analyse the light curves is a Fortran 2003 code that can be obtained from the first author on reasonable request. The HiPERCAM pipeline is available at https://cygnus.astro.warwick.ac.uk/phsaap/hipercam/docs/html/. The SHERLOCK package used to search for planets in the TESS data is publicly available at https://github.com/franpoz/SHERLOCK. The detection limits in the TESS data were computed using the MATRIX package, which is publicly available at https://github.com/PlanetHunters/tkmatrix. The code used to create Extended Data Fig. 1 is available at https://github.com/jpdeleon/epoch. The Generic Planetary Climate Model code (and documentation on how to use the model) used in this work can be downloaded from the SVN repository at https://svn.lmd.jussieu.fr/Planeto/trunk/LMDZ.GENERIC/. The Donuts code is available at https://github.com/jmccormac01/Donuts. More information and documentation are available at http://www-planets.lmd.jussieu.fr. The kastredux code used to reduce the Kast optical spectrum is available at https://github.com/aburgasser/kastredux.
References
Kirkpatrick, J. D., Henry, T. J. & Irwin, M. J. Ultra-cool M dwarfs discovered by QSO surveys. I: the APM objects. Astron. J. 113, 1421–1428 (1997).
Dieterich, S. B. et al. The solar neighborhood. XXXII. The hydrogen burning limit. Astron. J. 147, 94 (2014).
Gillon, M. Searching for red worlds. Nat. Astron. 2, 344 (2018).
Burdanov, A., Delrez, L., Gillon, M. & Jehin, E. in Handbook of Exoplanets (eds Deeg, H. J. & Belmonte, J. A.) 1007–1023 (Springer, 2018).
Delrez, L. et al. SPECULOOS: a network of robotic telescopes to hunt for terrestrial planets around the nearest ultracool dwarfs. In Proc. SPIE 10700, Ground-Based and Airborne Telescopes VII (eds Marshall, H. K. & Spyromilio, J.) 107001I (SPIE, 2018).
Sebastian, D. et al. SPECULOOS: ultracool dwarf transit survey. Target list and strategy. Astron. Astrophys. 645, A100 (2021).
Jehin, E. et al. The SPECULOOS Southern Observatory begins its hunt for rocky planets. Messenger 174, 2–7 (2018).
Burdanov, A. Y. et al. SPECULOOS Northern Observatory: searching for red worlds in the northern skies. Publ. Astron. Soc. Pac. 134, 105001 (2022).
Demory, B. O. et al. A super-Earth and a sub-Neptune orbiting the bright, quiet M3 dwarf TOI-1266. Astron. Astrophys. 642, A49 (2020).
Gillon, M., Jehin, E., Fumel, A., Magain, P. & Queloz, D. TRAPPIST-UCDTS: a prototype search for habitable planets transiting ultra-cool stars. EPJ Web Conf. 47, 03001 (2013).
Gillon, M. et al. Temperate Earth-sized planets transiting a nearby ultracool dwarf star. Nature 533, 221–224 (2016).
Gillon, M. et al. Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1. Nature 542, 456–460 (2017).
Delrez, L. et al. Two temperate super-Earths transiting a nearby late-type M dwarf. Astron. Astrophys. 667, A59 (2022).
Stassun, K. G., Corsaro, E., Pepper, J. A. & Gaudi, B. S. Empirical accurate masses and radii of single stars with TESS and Gaia. Astron. J. 155, 22 (2018).
Birky, J., Hogg, D. W., Mann, A. W. & Burgasser, A. Temperatures and metallicities of M dwarfs in the APOGEE Survey. Astrophys. J. 892, 31 (2020).
Stelzer, B., Marino, A., Micela, G., López-Santiago, J. & Liefke, C. The UV and X-ray activity of the M dwarfs within 10 pc of the Sun. Mon. Not. R. Astron. Soc. 431, 2063–2079 (2013).
Lopez, E. D., Fortney, J. J. & Miller, N. How thermal evolution and mass-loss sculpt populations of super-Earths and sub-Neptunes: application to the Kepler-11 system and beyond. Astrophys. J. 761, 59 (2012).
Owen, J. E. & Mohanty, S. Habitability of terrestrial-mass planets in the HZ of M Dwarfs - I. H/He-dominated atmospheres. Mon. Not. R. Astron. Soc. 459, 4088–4108 (2016).
Owen, J. E. & Wu, Y. Kepler planets: a tale of evaporation. Astrophys. J. 775, 105 (2013).
Owen, J. E. & Wu, Y. The evaporation valley in the Kepler planets. Astrophys. J. 847, 29 (2017).
Fulton, B. J. et al. The California-Kepler Survey. III. A gap in the radius distribution of small planets. Astron. J. 154, 109 (2017).
Luque, R. & Pallé, E. Density, not radius, separates rocky and water-rich small planets orbiting M dwarf stars. Science 377, 1211–1214 (2022).
Petigura, E. A. et al. The California-Kepler Survey. X. The radius gap as a function of stellar mass, metallicity, and age. Astron. J. 163, 179 (2022).
Akeson, R. L. et al. The NASA Exoplanet Archive: data and tools for exoplanet research. Publ. Astron. Soc. Pac. 125, 989 (2013).
Izidoro, A. et al. Breaking the chains: hot super-Earth systems from migration and disruption of compact resonant chains. Mon. Not. R. Astron. Soc. 470, 1750–1770 (2017).
Izidoro, A. et al. Formation of planetary systems by pebble accretion and migration. Hot super-Earth systems from breaking compact resonant chains. Astron. Astrophys. 650, A152 (2021).
Goldberg, M. & Batygin, K. Architectures of compact super-Earth systems shaped by instabilities. Astron. J. 163, 201 (2022).
Forget, F. & Leconte, J. Possible climates on terrestrial exoplanets. Phil. Trans. R. Soc. A 372, 20130084 (2014).
Zahnle, K. J. & Catling, D. C. The cosmic shoreline: the evidence that escape determines which planets have atmospheres, and what this may mean for Proxima Centauri B. Astrophys. J. 843, 122 (2017).
Grenfell, J. L. et al. Possible atmospheric diversity of low mass exoplanets - some central aspects. Space Sci. Rev. 216, 98 (2020).
Lim, O. et al. Atmospheric reconnaissance of TRAPPIST-1 b with JWST/NIRISS: evidence for strong stellar contamination in the transmission spectra. Astrophys. J. Lett. 955, L22 (2023).
Greene, T. P. et al. Thermal emission from the Earth-sized exoplanet TRAPPIST-1 b using JWST. Nature 618, 39–42 (2023).
Zieba, S. et al. No thick carbon dioxide atmosphere on the rocky exoplanet TRAPPIST-1 c. Nature 620, 746–749 (2023).
Mansfield, M. et al. Identifying atmospheres on rocky exoplanets through inferred high albedo. Astrophys. J. 886, 141 (2019).
Kempton, E. M.-R. et al. A framework for prioritizing the TESS planetary candidates most amenable to atmospheric characterization. Publ. Astron. Soc. Pac. 130, 114401 (2018).
Rackham, B. V., Apai, D. & Giampapa, M. S. The transit light source effect: false spectral features and incorrect densities for M-dwarf transiting planets. Astrophys. J. 853, 122 (2018).
May, E. M. et al. Double trouble: two transits of the super-Earth GJ 1132 b observed with JWST NIRSpec G395H. Astrophys. J. Lett. 959, L9 (2023).
Hapke, B. Space weathering from Mercury to the asteroid belt. J. Geophys. Res. 106, 10039–10074 (2001).
Lépine, S. & Shara, M. M. A catalog of northern stars with annual proper motions larger than 0.15” (LSPM-NORTH Catalog). Astron. J. 129, 1483–1522 (2005).
Dittmann, J. A., Irwin, J. M., Charbonneau, D. & Berta-Thompson, Z. K. Trigonometric parallaxes for 1507 nearby mid-to-late M dwarfs. Astrophys. J. 784, 156 (2014).
Gilhool, S. H. et al. The rotation of M dwarfs observed by the Apache Point Galactic Evolution Experiment. Astron. J. 155, 38 (2018).
Jönsson, H. et al. APOGEE data and spectral analysis from SDSS Data Release 16: seven years of observations including first results from APOGEE-South. Astron. J. 160, 120 (2020).
Gaia Collaboration. Gaia Data Release 2. Summary of the contents and survey properties. Astron. Astrophys. 616, A1 (2018).
Scholz, R. D. New ultracool dwarf neighbours within 20 pc from Gaia DR2. Astron. Astrophys. 637, A45 (2020).
Rayner, J. T. et al. SpeX: a medium-resolution 0.8-5.5 micron spectrograph and imager for the NASA Infrared Telescope Facility. Publ. Astron. Soc. Pac. 115, 362–382 (2003).
Cushing, M. C., Vacca, W. D. & Rayner, J. T. Spextool: a spectral extraction package for SpeX, a 0.8-5.5 micron cross-dispersed spectrograph. Publ. Astron. Soc. Pac. 116, 362–376 (2004).
Burgasser, A. J. & Splat Development Team. The SpeX Prism Library Analysis Toolkit (SPLAT): a data curation model. In 3rd International Workshop on Spectral Stellar Libraries, Astronomical Society of India Conference (eds Coelho, P. et al.) 7–12 (Astronomical Society of India, 2017).
Cushing, M. C., Rayner, J. T. & Vacca, W. D. An infrared spectroscopic sequence of M, L, and T dwarfs. Astron. J. 623, 1115–1140 (2005).
Rayner, J. T., Cushing, M. C. & Vacca, W. D. The Infrared Telescope Facility (IRTF) spectral library: cool stars. Astrophys. J. Suppl. Ser. 185, 289–432 (2009).
Kirkpatrick, J. D. et al. Discoveries from a near-infrared proper motion survey using multi-epoch two micron All-Sky Survey data. Astrophys. J. Suppl. Ser. 190, 100–146 (2010).
Mann, A. W. et al. Prospecting in ultracool dwarfs: measuring the metallicities of mid- and late-M dwarfs. Astron. J. 147, 160 (2014).
Miller, J. S. & Stone, R. P. S. The Kast Double Spectrograph Technical Report No. 66 (Univ. California Lick Observatory, 1994).
Kesseli, A. Y. et al. An empirical template library of stellar spectra for a wide range of spectral classes, luminosity classes, and metallicities using SDSS BOSS spectra. Astrophys. J. Suppl. Ser. 230, 16 (2017).
Gizis, J. E. M-subdwarfs: spectroscopic classification and the metallicity scale. Astron. J. 113, 806–822 (1997).
Martín, E. L. et al. Spectroscopic classification of late-M and L field dwarfs. Astron. J. 118, 2466–2482 (1999).
Lépine, S., Rich, R. M. & Shara, M. M. Spectroscopy of new high proper motion stars in the northern sky. I. New nearby stars, new high-velocity stars, and an enhanced classification scheme for M dwarfs. Astron. J. 125, 1598–1622 (2003).
Lépine, S. et al. A spectroscopic catalog of the brightest (J < 9) M dwarfs in the northern sky. Astron. J. 145, 102 (2013).
Mann, A. W., Brewer, J. M., Gaidos, E., Lépine, S. & Hilton, E. J. Prospecting in late-type dwarfs: a calibration of infrared and visible spectroscopic metallicities of late K and M dwarfs spanning 1.5 dex. Astron. J. 145, 52 (2013).
Stassun, K. G. & Torres, G. Parallax systematics and photocenter motions of benchmark eclipsing binaries in Gaia EDR3. Astrophys. J. Lett. 907, L33 (2021).
Stassun, K. G. & Torres, G. Eclipsing binaries as benchmarks for trigonometric parallaxes in the Gaia era. Astron. J. 152, 180 (2016).
Stassun, K. G., Collins, K. A. & Gaudi, B. S. Accurate empirical radii and masses of planets and their host stars with Gaia parallaxes. Astron. J. 153, 136 (2017).
Husser, T. O. et al. A new extensive library of PHOENIX stellar atmospheres and synthetic spectra. Astron. Astrophys. 553, A6 (2013).
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).
Mann, A. W. et al. How to constrain your M dwarf. II. The mass-luminosity-metallicity relation from 0.075 to 0.70 solar masses. Astrophys. J. 871, 63 (2019).
Czesla, S. et al. PyA: Python astronomy-related packages. Astrophysics Source Code Library ascl:1906.010 (2019).
Johnson, D. R. H. & Soderblom, D. R. Calculating galactic space velocities and their uncertainties, with an application to the Ursa Major group. Astron. J. 93, 864 (1987).
Gaia Collaboration. Gaia Early Data Release 3. Summary of the contents and survey properties. Astron. Astrophys. 649, A1 (2021).
Coşkunoğlu, B. et al. Local stellar kinematics from RAVE data - I. Local standard of rest. Mon. Not. R. Astron. Soc. 412, 1237–1245 (2011).
Li, C. & Zhao, G. The evolution of the galactic thick disk with the LAMOST Survey. Astrophys. J. 850, 25 (2017).
Buder, S. et al. The GALAH+ survey: third data release. Mon. Not. R. Astron. Soc. 506, 150–201 (2021).
Fernandes, C. S. et al. Evolutionary models for ultracool dwarfs. Astrophys. J. 879, 94 (2019).
Lightkurve Collaboration et al. Lightkurve: Kepler and TESS time series analysis in Python. Astrophysics Source Code Library ascl:1812.013 (2018).
Narita, N. et al. MuSCAT2: four-color simultaneous camera for the 1.52-m Telescopio Carlos Sánchez. J. Astron. Telesc. Instrum. Syst. 5, 015001 (2019).
Narita, N. et al. MuSCAT3: a 4-color simultaneous camera for the 2m Faulkes Telescope North. In Proc. Ground-based and Airborne Instrumentation for Astronomy VIII (eds Evans, C. J. et al.) 114475K (SPIE, 2020).
McCully, C. et al. in Software and Cyberinfrastructure for Astronomy V Conference Series Vol. 10707 (eds Guzman, J. C. & Ibsen, J.) 107070K (SPIE, 2018).
Garcia, L. J. et al. PROSE: a PYTHON framework for modular astronomical images processing. Mon. Not. R. Astron. Soc. 509, 4817–4828 (2022).
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).
Barkaoui, K. et al. Discovery of three new transiting hot Jupiters: WASP-161 b, WASP-163 b, and WASP-170 b. Astron. J. 157, 43 (2019).
Collins, K. A., Kielkopf, J. F., Stassun, K. G. & Hessman, F. V. AstroImageJ: image processing and photometric extraction for ultra-precise astronomical light curves. Astron. J. 153, 77 (2017).
Dhillon, V. S. et al. HiPERCAM: a quintuple-beam, high-speed optical imager on the 10.4-m Gran Telescopio Canarias. Mon. Not. R. Astron. Soc. 507, 350–366 (2021).
Stetson, P. B. DAOPHOT: a computer program for crowded-field stellar photometry. Publ. Astron. Soc. Pac. 99, 191 (1987).
Quirrenbach, A. et al. The CARMENES M-dwarf planet survey. In Proc. SPIE 11447, Ground-based and Airborne Instrumentation for Astronomy VIII (eds Evans, C. J. et al.) 114473C (SPIE, 2020).
Caballero, J. A. et al. in Observatory Operations: Strategies, Processes, and Systems VI Conference Series Vol. 9910 (eds Peck, A. B. et al.) 99100E (SPIE, 2016).
Zechmeister, M. et al. Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicators. Astron. Astrophys. 609, A12 (2018).
Scott, N. J. et al. Twin high-resolution, high-speed imagers for the Gemini telescopes: instrument description and science verification results. Front. Astron. Space Sci. 8, 138 (2021).
Howell, S. B. & Furlan, E. Speckle interferometric observations with the Gemini 8-m telescopes: signal-to-noise calculations and observational results. Front. Astron. Space Sci. 9, 871163 (2022).
Howell, S. B. et al. Speckle imaging excludes low-mass companions orbiting the exoplanet host star TRAPPIST-1. Astrophys. J. Lett. 829, L2 (2016).
Howell, S. B., Everett, M. E., Sherry, W., Horch, E. & Ciardi, D. R. Speckle camera observations for the NASA Kepler Mission follow-up program. Astron. J. 142, 19 (2011).
Baraffe, I., Homeier, D., Allard, F. & Chabrier, G. New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit. Astron. Astrophys. 577, A42 (2015).
Skrutskie, M. F. et al. The Two Micron All Sky Survey (2MASS). Astron. J. 131, 1163–1183 (2006).
Gillon, M. et al. The Spitzer search for the transits of HARPS low-mass planets. I. No transit for the super-Earth HD 40307b. 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).
Schwarz, G. Estimating the dimension of a model. Ann. Stat. 6, 461–464 (1978).
Matsumura, S., Takeda, G. & Rasio, F. A. On the origins of eccentric close-in planets. Astrophys. J. Lett. 686, L29 (2008).
Claret, A., Hauschildt, P. H. & Witte, S. New limb-darkening coefficients for PHOENIX/1D model atmospheres. I. Calculations for 1500 K ≤ Teff≤ 4800 K Kepler, CoRot, Spitzer, uvby, UBVRIJHK, Sloan, and 2MASS photometric systems. Astron. Astrophys. 546, A14 (2012).
Gelman, A. & Rubin, D. B. Inference from iterative simulation using multiple sequences. Stat. Sci. 7, 457–472 (1992).
Gillon, M. et al. An educated search for transiting habitable planets: targetting M dwarfs with known transiting planets. Astron. Astrophys. 525, A32 (2011).
Hippke, M. & Heller, R. Optimized transit detection algorithm to search for periodic transits of small planets. Astron. Astrophys. 623, A39 (2019).
Pozuelos, F. J. et al. GJ 273: on the formation, dynamical evolution, and habitability of a planetary system hosted by an M dwarf at 3.75 parsec. Astron. Astrophys. 641, A23 (2020).
Dévora-Pajares, M. & Pozuelos, F. J. MATRIX: multi-phase transits recovery from injected exoplanets toolkit. Astrophysics Source Code Library ascl:2309.007 (2023).
Seifahrt, A. et al. On-sky commissioning of MAROON-X: a new precision radial velocity spectrograph for Gemini North. In Proc. SPIE 11447, Ground-based and Airborne Instrumentation for Astronomy VIII (eds Evans, C. J. et al.) 114471F (SPIE, 2020).
Hatzes, A. P., Cochran, W. D. & Endl, M. in Planets in Binary Star Systems Astrophysics and Space Science Library Vol. 366 (ed Haghighipour, N.) 51–76 (Astrophysics and Space Science Library, 2010).
Rackham, B. V., Apai, D. & Giampapa, M. S. The transit light source effect. II. The impact of stellar heterogeneity on transmission spectra of planets orbiting broadly Sun-like stars. Astron. J. 157, 96 (2019).
Rackham, B. V. et al. The effect of stellar contamination on low-resolution transmission spectroscopy: needs identified by NASA’s Exoplanet Exploration Program Study Analysis Group 21. RAS Techniq. Instrum. 2, 148–206 (2023).
Leconte, J. et al. 3D climate modeling of close-in land planets: circulation patterns, climate moist bistability, and habitability. Astron. Astrophys. 554, A69 (2013).
Turbet, M. et al. Water condensation zones around main sequence stars. Astron. Astrophys. 679, A126 (2023).
Hu, R., Ehlmann, B. L. & Seager, S. Theoretical spectra of terrestrial exoplanet surfaces. Astrophys. J. 752, 7 (2012).
Lyu, X. et al. Super-Earth LHS3844b is tidally locked. Astrophys. J. 964, 152 (2024).
Batalha, N. E. et al. PandExo: a community tool for transiting exoplanet science with JWST & HST. Publ. Astron. Soc. Pac. 129, 064501 (2017).
Bouwman, J. et al. Spectroscopic time series performance of the mid-infrared instrument on the JWST. Publ. Astron. Soc. Pac. 135, 038002 (2023).
Whittaker, E. A. et al. The detectability of rocky planet surface and atmosphere composition with the JWST: the case of LHS 3844b. Astron. J. 164, 258 (2022).
Gillon, M. Detection of an Earth-sized exoplanet orbiting the nearby ultracool dwarf star SPECULOOS-3. Zenodo https://doi.org/10.5281/zenodo.10821723 (2024).
NASA Exoplanet Archive (California Institute of Technology, accessed 16 October 2023); https://exoplanetarchive.ipac.caltech.edu
Acknowledgements
The ULiege’s contribution to SPECULOOS has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013) (grant agreement number 336480/SPECULOOS), the Balzan Prize and Francqui Foundations, the Belgian Scientific Research Foundation (F.R.S.-FNRS; grant number T.0109.20), the University of Liege and the ARC grant for Concerted Research Actions financed by the Wallonia-Brussels Federation. M. Gillon is an F.R.S-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 Interdisciplinary Networks programme. E.J. is an F.R.S-FNRS Senior Research Associate. V.V.G. is an F.R.S-FNRS Research Associate. The postdoctoral fellowship of K.B. is funded by F.R.S.-FNRS grant number T.0109.20 and by the Francqui Foundation. This publication benefits from the support of the French Community of Belgium in the context of the FRIA Doctoral Grant awarded to M. Timmermans. This work is supported by a grant from the Simons Foundation (PI D.Q., grant number 327127). J.d.W. and MIT gratefully acknowledge financial support from the Heising-Simons Foundation, C. Masson and L. Masson and P. A. Gilman for Artemis, the first telescope of the SPECULOOS network situated in Tenerife, Spain. B.-O.D. acknowledges support from the Centre for Space and Habitability of the University of Bern and the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number MB22.00046. Part of this work received support from the National Centre for Competence in Research PlanetS, supported by the Swiss National Science Foundation (SNSF). The Birmingham contribution research is in part funded by the European Union’s Horizon 2020 research and innovation programme (grant agreement number 803193/BEBOP), from the MERAC foundation and from the Science and Technology Facilities Council (STFC; grant numbers ST/S00193X/1 and ST/W000385/1). We thank the Belgian Federal Science Policy Office (BELSPO) for the provision of financial support in the framework of the PRODEX Programme of the European Space Agency (ESA) under contract number 4000142531. B.V.R. thanks the Heising-Simons Foundation for Support. B.V.R. is a 51 Pegasi b Fellow. This material is based upon work supported by the National Aeronautics and Space Administration under agreement number 80NSSC21K0593 for the programme ‘Alien Earths’. The results reported herein benefited from collaborations and/or information exchange within NASA’s Nexus for Exoplanet System Science (NExSS) research coordination network sponsored by NASA’s Science Mission Directorate. M. Turbet acknowledges support from the Tremplin 2022 programme of the Faculty of Science and Engineering of Sorbonne University. M. Turbet thanks the Generic PCM team for the teamwork development and improvement of the model and acknowledges support from the High-Performance Computing (HPC) resources of Centre Informatique National de l’Enseignement Supérieur (CINES) under the allocation numbers A0100110391, A0120110391 and A0140110391 made by Grand Équipement National de Calcul Intensif (GENCI). M.R.S acknowledges support from the European Space Agency as an ESA Research Fellow. E.A.M.V. acknowledges support from the Centre for Space and Habitability (CSH). This work has been carried out within the framework of the National Centre of Competence in Research PlanetS supported by the Swiss National Science Foundation under grant numbers 51NF40_182901 and 51NF40_205606. This work is based upon observations carried out at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir (OAN-SPM), Baja California, México. SAINT-EX observations and team were supported by the Swiss National Science Foundation (grant numbers PP00P2-163967 and PP00P2-190080), the Centre for Space and Habitability (CSH) of the University of Bern and the National Centre for Competence in Research PlanetS, supported by the SNSF. Y.G.M.C. acknowledges support from UNAM PAPIIT-IG101224. Based on observations made with the GTC telescope, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, under Director’s Discretionary Time. Some of the observations in this paper made use of the High-Resolution Imaging instrument ‘Alopeke and were obtained under Gemini LLP proposal number GN-2023B-DD-101. ‘Alopeke was funded by the NASA Exoplanet Exploration Program and built at the NASA Ames Research Center by S.B.H., N. Scott, E. P. Horch and E. Quigley. ‘Alopeke was mounted on the Gemini North telescope of the international Gemini Observatory, a programme of the NSF’s OIR Lab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil) and Korea Astronomy and Space Science Institute (Republic of Korea). F.J.P., P.J.A., A.S., R.V., and J.A. acknowledge financial support from the Severo Ochoa grant CEX2021-001131-S funded by the Spanish Ministry of Science and Innovation grant MCIN/AEI/10.13039/501100011033. This work benefits from observations made at the Sierra Nevada Observatory, operated by the Instituto de Astrofísica de Andalucía (IAA-CSIC). D.K. and X.L. acknowledge financial support from NSFC grant number 42250410318. F.S. acknowledges support from CNES, Programme National de Planétologie (PNP) and the Investments for the Future programme IdEx, Université de Bordeaux/RRI ORIGINS. This research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). This work is partly supported by MEXT/JSPS KAKENHI grant numbers JP15H02063, JP18H05439, JP18H05442, JP21K13955, JP21K20376 and JP22000005 and JST CREST grant number JPMJCR1761. This paper is based on observations made with the MuSCAT3 instrument, developed by the Astrobiology Center and under financial supports by JSPS KAKENHI (grant number JP18H05439) and JST PRESTO (grant number JPMJPR1775), at Faulkes Telescope North on Maui, HI, operated by the Las Cumbres Observatory. Observations made with the Wide-Field Camera (WFCam) on the UKIRT telescope were granted through Director’s Discretionary Time. UKIRT is owned by the University of Hawaii (UH) and operated by the UH Institute for Astronomy. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. The Digitized Sky Surveys were produced at the Space Telescope Science Institute under US Government grant number NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of these institutions. The National Geographic Society–Palomar Observatory Sky Atlas (POSS-I) was made by the California Institute of Technology with grants from the National Geographic Society. The Second Palomar Observatory Sky Survey (POSS-II) was made by the California Institute of Technology with funds from the National Science Foundation, the National Geographic Society, the Sloan Foundation, the Samuel Oschin Foundation and the Eastman Kodak Corporation. The Oschin Schmidt Telescope is operated by the California Institute of Technology and Palomar Observatory. The UK Schmidt Telescope was operated by the Royal Observatory Edinburgh, with funding from the UK Science and Engineering Research Council (later the UK Particle Physics and Astronomy Research Council) until June 1988, and thereafter by the Anglo-Australian Observatory. The blue plates of the southern Sky Atlas and its Equatorial Extension (together known as the SERC-J), as well as the Equatorial Red (ER) and the Second Epoch [red] Survey (SES), were all taken with the UK Schmidt Telescope. Supplemental funding for sky-survey work at the STScI is provided by the European Southern Observatory.
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M. Gillon initiated the SPECULOOS project, performed the analyses of the photometry described in this paper and wrote a large part of the paper. M. Gillon, B.-O.D., J.d.W., D.Q. and A.H.M.J.T. led the SPECULOOS project and manage its funding, its organization and its operations. P.P.P. developed and maintains the SPECULOOS database and its web interface, a key element in the discovery of the planet. B.V.R. and C.A.T. acquired, reduced and analysed the SpeX spectra, and B.V.R. analysed the TESS data with J.d.W. E.D. managed the scheduling of the SPECULOOS observations. A.Y.B. managed operations of the SPECULOOS-North facility. S.Z.-F. managed the SPECULOOS-South Observatory facilities. M.J.H. managed the SPECULOOS data analysis pipeline. This role was previously in the hands of C.A.M. (who developed the pipeline). M. Gillon, A.H.M.J.T., B.-O.D., G.D., Y.T.D., M.R.S., T.B., M.J.H., S.J.T., C.J.M., E.D., K.B., P.P.P., A.Y.B., L.D., M. Timmermans, F.J.P., S.Z.-F., E.J., L.J.G., C.A.M., D.B., F.D., S.H., Y.S., Z.L.d.B. and P.N. operated the SPECULOOS telescopes. E.D., G.D., L.D., D.S., M. Timmermans, F.J.P. and S.Z.-F. examined the SPECULOOS light curves on a daily basis to search for any structure that could be related to the transit of an exoplanet, and identified the first transits of the planet. L.J.G. contributed to the data management and maintenance of the SPECULOOS different observatories. M.N.G. contributed to the search for SPECULOOS candidates in the TESS data, and provided comments on the paper. M.S. provided comments on the paper. K.G.S. performed the spectral energy distribution analysis. S.M.L. led the UKIRT observation proposal, and managed the scheduling of the UKIRT observations. A.J.B. and R.G. acquired, reduced and analysed the Kast optical spectrum. C.A. led the kinematic and metallicity age analysis. S.B.H. obtained the Gemini high-resolution speckle observations, reduced the data and provided their analysis. S.B.H. also provided comments on the paper. Z.B. managed the Oukaimeden Observatory hosting TRAPPIST-North. M. Ghachoui scheduled and performed the TRAPPIST-North observations. K.B. provided SPECULOOS, Saint-EX, TRAPPIST-North and MuSCAT3 data reduction. N.N. obtained MuSCAT3 Director’s Discretionary Time and performed all MuSCAT3 observations. J.P.d.L. reduced data from MuSCAT2 and part of the data from MuSCAT3. N.N., J.P.d.L., A.F., I.F., Y.H., K. Ikuta, K. Isogai, M.I., K.K., T.K., Y.K., J.H.L., M.M., M. Tamura, Y.T. and N.W. provided MuSCAT3 GTO for this project. N.N. and E.P. provided MuSCAT2 observations for this project. F.M. performed MuSCAT2 observations. C.A.C. provided the ‘Alopeke data reduction. R.A. and R.R. wrote the GTC/HiPERCAM observation proposal, and R.A. reduced the data. F.J.P. searched for extra planets in the TESS data and established detection limits. F.J.P. also scheduled, reduced and analysed the T150 photometric data, and provided the CARMENES data. P.J.A., J.A. and R.V. wrote the CARMENES proposal and managed the schedule of observations and data reduction and analysis. D.S. assessed the potential to measure the planets mass using high-resolution spectroscopy. A.S. operated the T150 telescope. L.D. and E.D. assessed the potential of the planet for emission spectroscopy with JWST and performed the corresponding PandExo simulations. R.H., D.D.B.K. and X.L. provided model emission spectra for various surface compositions. M. Turbet and F.S. performed 3D numerical climate model simulations of SPECULOOS-3 b for two plausible atmospheres, and provided associated emission spectra. E.B. provided guidance and comments on the paper. S.J.T. helped in the design and commissioning of the SPECULOOS-South Observatory and is a member of the operations team. F.S. worked on synthetic observations with JWST. J.J.M. implemented a custom autoguiding routine for each SPECULOOS node based on his open source Donuts science frame autoguiding algorithm, with the goal of minimizing star drift and systematic noise in the observations. M.J.H. mainlined and developed the pipeline that automatically processes all SPECULOOS data at the University of Cambridge and provided an initial fit to the SPECULOOS and TESS transit light curves. V.V.G. ran stellar evolution modelling to derive host star properties. B.-O.D., U.S., Y.G.M.C., D.K., E.A.M.V., I.P.-F., L.S., N.S. and F.Z.L. operated the SAINT-EX telescope, including scheduling observations, nightly operations, data processing and maintenance of the facility. K.H. and M. L. contributed to the funding of SAINT-EX.
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Extended data
Extended Data Fig. 1 Evolution of the position of SPECULOOS-3.
Left: Archival image of the target taken in 1951 using a photographic plate on the Palomar Schmidt Telescope as part of the National Geographic Society - Palomar Observatory Sky Atlas (POSS-I) survey. Right: MuSCAT3 zs band image taken in 2023. The 7 decade-long baseline allowed the target move more than half a degree showing a clear line-of-sight at the past (red circle) and current (blue circle) positions of the target.
Extended Data Fig. 2 Speckle imaging of SPECULOOS-3.
Result from speckle imaging with the ’Alopeke instrument mounted on the 8-m Gemini-North telescope, on Maunea Kea, Hawai’i. The inset on the top right shows the final image produced by our analysis, which is summarized by the two curves of the main figure. These curves show the sensitivity in two bands (blue = 562 nm and red = 832 nm). The observations reveal there are no companions with a brightness greater than 5 to 6 magnitudes at distances above 0.1” from SPECULOOS-3A, which corresponds to a physical distance of approximately 1.7 AU.
Extended Data Fig. 3 Spectral energy distribution of SPECULOOS-3.
Red symbols represent the observed photometric measurements, where the horizontal bars represent the effective width of the bandpass, and the vertical bars the 1 − σ error bars on the measurements. Blue symbols are the model fluxes from the best-fit PHOENIX atmosphere model (black). Overlaid on the model are the absolute flux-calibrated spectrophotometric observations from SpeX (gray swathe) and Kast (yellow).
Extended Data Fig. 4 Effect of space weathering on the emission spectrum of an airless SPECULOOS-3b.
Mid-infrared eclipse depths increase with stronger weathering of an ultramafic surface (see Methods for details).
Supplementary information
Supplementary Information
Supplementary Figs. 1 and 2 and Tables 1–3.
Source data
Source Data Fig. 1
Processed data.
Source Data Fig. 2
Processed data.
Source Data Fig. 3
Processed data.
Source Data Fig. 4
Archival data from the NASA Exoplanet archive.
Source Data Fig. 5
Simulated data.
Source Data Extended Data Fig. 2
Processed data.
Source Data Extended Data Fig. 3
Processed data and model.
Source Data Extended Data Fig. 4
Simulated data.
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Gillon, M., Pedersen, P.P., Rackham, B.V. et al. Detection of an Earth-sized exoplanet orbiting the nearby ultracool dwarf star SPECULOOS-3. Nat Astron (2024). https://doi.org/10.1038/s41550-024-02271-2
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DOI: https://doi.org/10.1038/s41550-024-02271-2
