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

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.

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.

Extended Data Fig. 1 Evolution of the position of SPECULOOS-3.

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.

The authors declare no competing interests.