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Detection of an Earth-sized exoplanet orbiting the nearby ultracool dwarf star SPECULOOS-3

Original source (on modern site)

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.


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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.

Author information

Authors and Affiliations

  1. Astrobiology Research Unit, Université de Liège, Liège, Belgium

    Michaël Gillon, Elsa Ducrot, Khalid Barkaoui, Laetitia Delrez, Lionel J. Garcia, Mathilde Timmermans, Sebastián Zúñiga-Fernández, Fatemeh Davoudi, Mourad Ghachoui & Manu Stalport

  2. Cavendish Laboratory, Cambridge, UK

    Peter P. Pedersen, Didier Queloz, Matthew J. Hooton, Clàudia Jano Muñoz & Samantha J. Thompson

  3. Department of Physics, ETH Zurich, Zurich, Switzerland

    Peter P. Pedersen, Didier Queloz, David Berardo & Yannick Schackey

  4. Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, Cambridge, MA, USA

    Benjamin V. Rackham, Khalid Barkaoui, Artem Y. Burdanov, Julien de Wit, Zoë L. de Beurs, Samantha Hasler & Prajwal Niraula

  5. Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA

    Benjamin V. Rackham & David Berardo

  6. School of Physics & Astronomy, University of Birmingham, Birmingham, UK

    Georgina Dransfield, Amaury H. M. J. Triaud, Daniel Sebastian, Thomas Baycroft, Yasmin T. Davis & Matthew R. Standing

  7. LESIA, Observatoire de Paris, CNRS, Université Paris Diderot, Université Pierre et Marie Curie, Meudon, France

    Elsa Ducrot & Enric Pallé

  8. Instituto de Astrofísica de Canarias (IAC), La Laguna, Spain

    Khalid Barkaoui, Roi Alonso, Norio Narita, Akihiko Fukui, Felipe Murgas & Rafael Rebolo

  9. Center for Space and Habitability, University of Bern, Bern, Switzerland

    Urs Schroffenegger, Brice-Olivier Demory, Daniel Kitzmann, Erik A. Meier Valdés & Francis Zong Lang

  10. Instituto de Astronomía, Universidad Nacional Autónoma de México, Mexico City, Mexico

    Yilen Gómez Maqueo Chew

  11. NASA Johnson Space Center, Houston, TX, USA

    Susan M. Lederer & Felipe Murgas

  12. Departamento de Astrofísica, Universidad de La Laguna, La Laguna, Spain

    Roi Alonso & Enric Pallé

  13. Department of Astronomy & Astrophysics, University of California San Diego, La Jolla, CA, USA

    Adam J. Burgasser, Christian Aganze, Roman Gerasimov & Christopher A. Theissen

  14. NASA Ames Research Center, Moffett Field, CA, USA

    Steve B. Howell

  15. Komaba Institute for Science, The University of Tokyo, Tokyo, Japan

    Norio Narita & Akihiko Fukui

  16. Astrobiology Center, Tokyo, Japan

    Norio Narita, John H. Livingston & Motohide Tamura

  17. Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Liège, Belgium

    Laetitia Delrez, Emmanuël Jehin, Manu Stalport & Valérie Van Grootel

  18. Institute of Astronomy, KU Leuven, Leuven, Belgium

    Laetitia Delrez

  19. Center for Computational Astrophysics, Flatiron Institute, New York, NY, USA

    Lionel J. Garcia

  20. Department of Astrophysical and Planetary Sciences, University of Colorado Boulder, Boulder, CO, USA

    Catriona A. Murray

  21. Instituto de Astrofísica de Andalucía (IAA-CSIC), Granada, Spain

    Francisco J. Pozuelos, Jesús Aceituno, Pedro J. Amado, Alfredo Sota & Roberto Varas

  22. Centro Astronómico Hispano en Andalucia, Gérgal, Spain

    Jesús Aceituno

  23. Department of Physics, Stanford University, Stanford, CA, USA

    Christian Aganze

  24. Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, Faculty of Sciences Semlalia, Cadi Ayyad University, Marrakech, Morocco

    Zouhair Benkhaldoun & Mourad Ghachoui

  25. Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA

    David Berardo

  26. Département d'astronomie de l'Université de Genève, Sauverny, Switzerland

    Emeline Bolmont & Monika Lendl

  27. Centre sur la Vie dans l'Univers, Université de Genève, Geneva, Switzerland

    Emeline Bolmont

  28. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

    Catherine A. Clark & Renyu Hu

  29. NASA Exoplanet Science Institute, IPAC, California Institute of Technology, Pasadena, CA, USA

    Catherine A. Clark

  30. Department of Multi-Disciplinary Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan

    Jerome P. de Leon, Kai Ikuta, Keisuke Isogai, Izuru Fukuda, Yuya Hayashi, Taiki Kagetani, Yugo Kawai, Mayuko Mori & Noriharu Watanabe

  31. Division of Science, National Astronomical Observatory of Japan, Tokyo, Japan

    Masahiro Ikoma

  32. Astronomical Science Program, Graduate University for Advanced Studies, Tokyo, Japan

    Masahiro Ikoma & John H. Livingston

  33. Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan

    Masahiro Ikoma

  34. Okayama Observatory, Kyoto University, Asakuchi, Japan

    Keisuke Isogai

  35. Department of Physics & Astronomy, University of Notre Dame, Notre Dame, IN, USA

    Roman Gerasimov

  36. European Space Research and Technology Centre (ESTEC), European Space Agency (ESA), Noordwijk, the Netherlands

    Maximilian N. Günther

  37. Faculty of Physics, Ludwig Maximilian University, Munich, Germany

    Kevin Heng

  38. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA

    Renyu Hu

  39. Department of Physical Sciences, Ritsumeikan University, Kusatsu, Japan

    Kiyoe Kawauchi

  40. Department of Atmospheric and Oceanic Sciences, Peking University, Beijing, China

    Daniel D. B. Koll & Xintong Lyu

  41. National Astronomical Observatory of Japan, Tokyo, Japan

    John H. Livingston & Motohide Tamura

  42. Department of Physics, University of Warwick, Coventry, UK

    James J. McCormac & Yuka Terada

  43. Instituto de Astronomía, Universidad Nacional Autónoma de México, Unidad Académica en Ensenada, Ensenada, Mexico

    Ilse Plauchu-Frayn, Laurence Sabin & Yuka Terada

  44. NASA Goddard Space Flight Center, Greenbelt, MD, USA

    Nicole Schanche

  45. Department of Astronomy, University of Maryland, College Park, MD, USA

    Nicole Schanche

  46. Laboratoire d'astrophysique de Bordeaux, Université Bordeaux, CNRS, Pessac, France

    Franck Selsis & Martin Turbet

  47. European Space Astronomy Centre (ESAC), European Space Agency (ESA), Madrid, Spain

    Matthew R. Standing

  48. Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, USA

    Keivan G. Stassun

  49. Department of Astronomy, University of Tokyo, Tokyo, Japan

    Motohide Tamura

  50. Laboratoire de Météorologie Dynamique/IPSL, CNRS, Sorbonne Université, Ecole Normale Supérieure, Université PSL, Ecole Polytechnique, Institut Polytechnique de Paris, Paris, France

    Martin Turbet


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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Correspondence to Michaël Gillon.

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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.

Source data

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).

Source data

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).

Source data

Extended Data Table 1 Detectability of atmospheres with MIRI/LRSExtended Data Table 2 Detectability of surface mineralogy with MIRI/LRS

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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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