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A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067

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Abstract

Planets with radii between that of the Earth and Neptune (hereafter referred to as ‘sub-Neptunes’) are found in close-in orbits around more than half of all Sun-like stars1,2. However, their composition, formation and evolution remain poorly understood3. The study of multiplanetary systems offers an opportunity to investigate the outcomes of planet formation and evolution while controlling for initial conditions and environment. Those in resonance (with their orbital periods related by a ratio of small integers) are particularly valuable because they imply a system architecture practically unchanged since its birth. Here we present the observations of six transiting planets around the bright nearby star HD 110067. We find that the planets follow a chain of resonant orbits. A dynamical study of the innermost planet triplet allowed the prediction and later confirmation of the orbits of the rest of the planets in the system. The six planets are found to be sub-Neptunes with radii ranging from 1.94R to 2.85R. Three of the planets have measured masses, yielding low bulk densities that suggest the presence of large hydrogen-dominated atmospheres.

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Fig. 1: Space-based photometry from the TESS and the CHEOPS of HD 110067.
Fig. 2: Radial velocity data from CARMENES and HARPS-N of HD 110067.
Fig. 3: Properties of the HD 110067 system compared with the known sub-Neptune-sized planet population.

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Data availability

The TESS observations used in this study are publicly available at the Mikulski Archive for Space Telescopes (https://archive.stsci.edu/missions-and-data/tess). The CHEOPS observations used in this study are available at the CHEOPS mission archive (https://cheops-archive.astro.unige.ch/archive_browser/). The ground-based photometry and high-resolution imaging observations are uploaded to ExoFOP (https://exofop.ipac.caltech.edu/tess/target.php?id=347332255) and are publicly available. CARMENES and HARPS-N reduced spectra, together with the derived CCF-based radial velocities and spectral indicators, are available at Zenodo (https://doi.org/10.5281/zenodo.8211589). All reduced transit photometry and radial velocity measurements used in this work are also provided at Zenodo (https://doi.org/10.5281/zenodo.8211589).

Code availability

We used the following publicly available codes, resources and Python packages to reduce, analyse and interpret our observations of HD 110067: numpy (ref. 155), matplotlib (ref. 156), astropy (ref. 157), lightkurve (ref. 44), PIPE (ref. 51,52), AstroImageJ (ref. 58), raccoon (ref. 73), serval (ref. 74), ARES (refs. 79,80), MOOG (ref. 81), ZASPE (ref. 83), emcee (ref. 158), CLES (ref. 96), exoplanet (ref. 99), MonoTools (ref. 106), pymc3 (ref. 117), ArviZ (ref. 120), GLS (ref. 121), MCMCI (ref. 132) and pyaneti (refs. 136,139). We can share the code used in the data reduction or data analysis on request.

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Acknowledgements

We acknowledge the use of public TESS data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center (SPOC). Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. The CHaracterising ExOPlanets Satellite (CHEOPS) is a European Space Agency (ESA) mission in partnership with Switzerland with important contributions to the payload and the ground segment from Austria, Belgium, France, Germany, Hungary, Italy, Portugal, Spain, Sweden and the United Kingdom. The CHEOPS Consortium would like to gratefully acknowledge the support received by all the agencies, offices, universities and industries involved. Their flexibility and willingness to explore new approaches were essential to the success of this mission. CARMENES acknowledges financial support from the Agencia Estatal de Investigación of the Ministerio de Ciencia e Innovación MCIN/AEI/10.13039/501100011033 and the European Regional Development Fund (ERDF) ‘A way of making Europe’ through projects PID2019-107061GB-C61, PID2019-107061GB-C66, PID2021-125627OB-C31 and PID2021-125627OB-C32, from the Centre of Excellence ‘Severo Ochoa’ award to the Instituto de Astrofísica de Canarias (IAC; CEX2019-000920-S), from the Centre of Excellence ‘María de Maeztu’ award to the Institut de Ciències de l’Espai (CEX2020-001058-M) and from the Generalitat de Catalunya/CERCA programme. Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the Istituto Nazionale di Astrofisica (INAF) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. This article is based on observations made with the MuSCAT2 instrument, developed by the Astrobiology Center (ABC), at Telescopio Carlos Sánchez operated on the island of Tenerife by the IAC in the Spanish Observatorio del Teide. This paper is based on observations made with the MuSCAT3 instrument, developed by ABC and under financial supports by JSPS KAKENHI (JP18H05439) and JST PRESTO (JPMJPR1775), at Faulkes Telescope North on Maui, Hawaii, operated by the Las Cumbres Observatory. Tierras is supported by grants from the John Templeton Foundation and the Harvard Origins of Life Initiative. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. The Next Generation Transit Survey (NGTS) facility is operated by the consortium institutes with support from the UK Science and Technology Facilities Council (STFC) under projects ST/M001962/1 and ST/S002642/1. Some of the observations presented in this paper were carried out at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir (OAN-SPM), Baja California, México. This work makes use of observations from the Las Cumbres Observatory global telescope network. 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-S-2021A-LP-105. Alopeke was funded by the NASA Exoplanet Exploration Program and built at the NASA Ames Research Center by S. B. Howell, N. Scott, E. P. Horch and E. Quigley. Alopeke was mounted on the Gemini North telescope of the international Gemini Observatory, a programme of NSF 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). This work was supported by the KESPRINT collaboration, an international consortium devoted to the characterization and research of exoplanets discovered with space-based missions. R.Lu. thanks D. Fabrycky for helpful discussions about the orbital dynamics of the HD 110067 system. R.Lu. acknowledges funding from University of La Laguna through the Margarita Salas Fellowship from the Spanish Ministry of Universities ref. UNI/551/2021-May 26 and under the EU Next Generation funds. This work has been carried out within the framework of the National Centre for Competence in Research (NCCR) PlanetS supported by the Swiss National Science Foundation (SNSF) under grants 51NF40_182901 and 51NF40_205606. A.C.Ca. and T.G.Wi. acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1 and UKSA grant number ST/R003203/1. O.Ba. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 865624). M.Le. acknowledges support of the SNSF under grant number PCEFP2_194576. P.F.L.Ma. acknowledges support from STFC research grant number ST/M001040/1. Y.Al. acknowledges support from the SNSF under grant 200020_192038. D.Ga. gratefully acknowledges financial support from the CRT foundation under grant no. 2018.2323 ‘Gaseous or rocky? Unveiling the nature of small worlds’. J.A.Eg. acknowledges support from the SNSF under grant 200020_192038. G.No. is grateful for the research funding from the Ministry of Education and Science programme ‘The Excellence Initiative – Research University’ conducted at the Centre of Excellence in Astrophysics and Astrochemistry of the Nicolaus Copernicus University in Torun, Poland. D.Ra. was supported by NASA under award number NNA16BD14C for NASA Academic Mission Services. M.La. acknowledges funding from a UKRI Future Leader Fellowship, grant number MR/S035214/1. V.Ad. is supported by Fundação para a Ciência e a Tecnologia (FCT) through national funds by grants UIDB/04434/2020, UIDP/04434/2020 and 2022.06962.PTDC. P.J.Am. acknowledges financial support from grants CEX2021-001131-S and PID2019-109522GB-C52, both funded by MCIN/AEI/ 10.13039/501100011033 and by the ERDF ‘A way of making Europe’. S.C.C.Ba. acknowledges support from FCT through FCT contract no. IF/01312/2014/CP1215/CT0004. X.Bo., S.Ch., D.Ga., M.Fr. and J.La. acknowledge their role as ESA-appointed CHEOPS science team members. L.Bo., V.Na., I.Pa., G.Pi., R.Ra., G.Sc., and T.Zi. acknowledge support from CHEOPS ASI-INAF agreement no. 2019-29-HH.0. A.Br. was supported by the Swedish National Space Agency (SNSA). Contributions at the Mullard Space Science Laboratory by E.M.Br. were supported by STFC through the consolidated grant ST/W001136/1. S.C.-G. acknowledges support from UNAM PAPIIT-IG101321. D.Ch. and J.G.-M. thank the staff at the F. L. Whipple Observatory for their assistance in the refurbishment and maintenance of the 1.3-m telescope. W.D.Co. acknowledges support from NASA grant 80NSSC23K0429. This is University of Texas Center for Planetary Systems Habitability Contribution 0063. K.A.Co. acknowledges support from the TESS mission through subaward s3449 from MIT. H.J.De. acknowledges support from the Spanish Research Agency of the Ministry of Science and Innovation (AEI-MICINN) under grant PID2019-107061GB-C66, doi:10.13039/501100011033. This project was supported by the CNES. The Belgian participation to CHEOPS has been supported by the Belgian Federal Science Policy Office (BELSPO) in the framework of the PRODEX Program and by the University of Liège through an ARC grant for Concerted Research Actions financed by the Wallonia-Brussels Federation. L.De. is an F.R.S.-FNRS Postdoctoral Researcher. This work was supported by FCT through national funds and by FEDER through COMPETE2020 – Programa Operacional Competitividade e Internacionalizacão by these grants: UID/FIS/04434/2019, UIDB/04434/2020, UIDP/04434/2020, PTDC/FIS-AST/32113/2017 and POCI-01-0145-FEDER-032113, PTDC/FIS-AST/28953/2017 and POCI-01-0145-FEDER-028953, PTDC/FIS-AST/28987/2017 and POCI-01-0145-FEDER-028987. O.D.S.De. is supported in the form of work contract (DL 57/2016/CP1364/CT0004) funded by national funds through FCT. B.-O.De. acknowledges support from the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number MB22.00046. This project has received funding from the ERC under the European Union’s Horizon 2020 research and innovation programme (project Four Aces grant agreement no. 724427). It has also been carried out in the frame of the NCCR PlanetS supported by the SNSF. D.Eh. acknowledges financial support from the SNSF for project 200021_200726. E.E.-B. acknowledges financial support from the European Union and the State Agency of Investigation of the Spanish Ministry of Science and Innovation (MICINN) under the grant PRE2020-093107 of the Pre-Doc Program for the Training of Doctors (FPI-SO) through FSE funds. M.Fr. gratefully acknowledges the support of the Swedish National Space Agency (DNR 65/19, 174/18). J.G.-M. acknowledges support by the National Science Foundation through a Graduate Research Fellowship under grant no. DGE1745303 and by the Ford Foundation through a Ford Foundation Predoctoral Fellowship, administered by the National Academies of Sciences, Engineering, and Medicine. The contributions at the University of Warwick by S.Gi. have been supported by STFC through consolidated grants ST/L000733/1 and ST/P000495/1. M.Gi. is F.R.S.-FNRS Research Director. Y.G.M.Ch. acknowledges support from UNAM PAPIIT-IG101321. E.Go. acknowledges support by the Thueringer Ministerium füër Wirtschaft, Wissenschaft und Digitale Gesellschaft. M.N.Gu. is the ESA CHEOPS Project Scientist and Mission Representative and, as such, is also responsible for the Guest Observers (GO) Programme. M.N.Gu. does not relay proprietary information between the GO and Guaranteed Time Observation (GTO) Programmes, and does not decide on the definition and target selection of the GTO Programme. A.P.Ha. acknowledges support by DFG grant HA 3279/12-1 within the DFG Schwerpunkt SPP 1992. Ch.He. acknowledges support from the European Union H2020-MSCA-ITN-2019 under grant agreement no. 860470 (CHAMELEON). S.Ho. gratefully acknowledges CNES funding through the grant 837319. This work is partly supported by JST CREST grant number JPMJCR1761. K.G.Is. is the ESA CHEOPS Project Scientist and is responsible for the ESA CHEOPS GO Programme. She does not participate in, or contribute to, the definition of the Guaranteed Time Programme of the CHEOPS mission through which observations described in this paper have been taken nor to any aspect of target selection for the programme. J.Ko. gratefully acknowledges the support of the SNSA (DNR 2020-00104) and of the Swedish Research Council (VR: Etableringsbidrag 2017-04945). K.W.F.La. was supported by Deutsche Forschungsgemeinschaft grants RA714/14-1 within the DFG Schwerpunkt SPP 1992, Exploring the Diversity of Extrasolar Planets. This work was granted access to the HPC resources of MesoPSL financed by the Region Ile de France and the project Equip@Meso (reference ANR-10-EQPX-29-01) of the programme Investissements d’Avenir supervised by the Agence Nationale pour la Recherche. A.L.desE. acknowledges support from the CNES (Centre national d’études spatiales, France). This work is partly supported by Astrobiology Center SATELLITE Research project AB022006. This work is partly supported by JSPS KAKENHI grant number JP18H05439 and JST CREST grant number JPMJCR1761. H.L.M.Os. acknowledges funding support by STFC through a PhD studentship. H.Pa. acknowledges the support by the Spanish Ministry of Science and Innovation with the Ramon y Cajal fellowship number RYC2021-031798-I. This work was also partially supported by a grant from the Simons Foundation (PI: Queloz, grant number 327127). S.N.Qu. acknowledges support from the TESS mission through subaward s3449 from MIT. S.N.Qu. acknowledges support from the TESS GI Program under award 80NSSC21K1056 (G03268). L.Sa. acknowledges support from UNAM PAPIIT project IN110122. N.C.Sa. acknowledges funding by the European Union (ERC, FIERCE, 101052347). Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union or the ERC. Neither the European Union nor the granting authority can be held responsible for them. N.Sc. acknowledges support from the SNSF (PP00P2-163967 and PP00P2-190080) and NASA under award number 80GSFC21M0002. S.G.So. acknowledges support from FCT through FCT contract no. CEECIND/00826/2018 and POPH/FSE (EC). Gy.M.Sz. acknowledges the support of the Hungarian National Research, Development and Innovation Office (NKFIH) grant K-125015, a PRODEX Experiment Agreement no. 4000137122, the Lendület LP2018-7/2021 grant of the Hungarian Academy of Science and the support of the city of Szombathely. A.Tu. acknowledges funding support from the STFC through a PhD studentship. V.V.Ey. acknowledges support by the STFC through the consolidated grant ST/W001136/1. V.V.Gr. is an F.R.S.-FNRS Research Associate. J.Ve. acknowledges support from the SNSF under grant PZ00P2_208945. N.A.Wa. acknowledges UKSA grant ST/R004838/1. N.Wa. is partly supported by JSPS KAKENHI grant number JP21K20376.

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Authors and Affiliations

Authors

Contributions

R.Lu., H.P.Os., A.Le., E.Pa., A.Bo., O.Ba. and T.G.Wi. conceived the project and contributed notably to the writing of this manuscript. R.Lu. and H.P.Os. led the analysis of the photometric data. A.Le. led the dynamical analysis of the system and developed the method with J.-B.De. to predict the orbits of the planets based on their resonant state within the chain. R.Lu., A.Bo. and O.Ba. led the analysis of the radial velocity data and the stellar activity mitigation. T.G.Wi. led the stellar characterization with the help of V.Ad., S.G.So., A.Bo., V.V.Gr., S.Sa. and W.D.Co. Y.Al. and J.A.Eg. led the analysis of the internal structures and L.Fo. and A.Bo. performed the atmospheric evolution simulations. D.Ra., J.D.Tw. and J.M.Je. improved the TESS data reduction to recover the missing cadences affected by reflected light and high background. R.Lu., E.Pa. and G.No. planned and obtained the time for the observations with CARMENES and HARPS-N. CARMENES observations were made possible by M.La., J.C.Mo., P.J.Am., A.Qu. and I.Ri. HARPS-N observations were made possible by I.Ca., J.O.-M., F.Mu., H.J.De., J.Ko., D.Ga., J.H.Li., W.D.Co., E.W.Gu., V.V.Ey., H.L.M.Os., S.Re., E.Go., F.Da. and K.W.F.La. High-resolution imaging observations from Palomar and Gemini North were made possible by A.W.Bo., D.R.Ci., I.J.M.Cr., S.B.Ho., E.Ma. and J.E.Sc. Ground-based photometric observations to catch the transit of planet f were made possible by the MuSCAT2 (R.Lu., E.Pa., N.Na., J.H.Li., K.Ik., E.E.-B., J.O.-M., N.Wa., F.Mu., G.No., A.Fu., H.Pa., M.Mo., T.Ka., J.P.D.Le. and T.Ko.), LCO (T.G.Wi., R.Lu., H.P.Os., E.Pa., A.Le., A.Tu., M.J.Ho., Y.Al. and D.Ga.), NGTS (H.P.Os., S.Gi., D.Ba., D.R.An., M.Mo., A.M.S.Sm., E.M.Br. and S.Ud.), Tierras (J.G.-M. and D.Ch.), SAINT-EX (N.Sc., Y.G.M.Ch., L.Sa., S.C.-G. and B.-O.De.) and MuSCAT3 (N.Na., J.H.Li., K.Ik., N.Wa., A.Fu., M.Mo., T.Ka., J.P.D.Le. and T.Ko.) instruments. The remaining authors provided key contributions to the development of the TESS and CHEOPS mission. All authors read and commented on the manuscript and helped with its revision.

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Correspondence to R. Luque.

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Extended data figures and tables

Extended Data Fig. 1 Transit duration versus transit depth for all unassigned transits in the TESS data.

TESS Sector 23 and Sector 49 are shown as different colours. The numbers above each transit denote the mid-transit time in TJD. Contours represent percentile levels, the innermost one corresponding to the 50th percentile and the outermost to the 99th percentile by increments of 10%. The transit of planet f in PLD photometry is marked with * to indicate that its properties are heavily affected by pretransit systematic noise.

Extended Data Fig. 2 Generalized three-body Laplace angles for known systems in resonant chains.

Included are the Galilean satellites Kepler-60 (refs. 12,115), Kepler-80 (ref. 159), K2-138 (ref. 112), Kepler-223 (ref. 110), TRAPPIST-1 (ref. 13) and TOI-178 (ref. 10). Measurements belonging to the same system are marked with the same colour. The line marks the observed distance to the theorized equilibrium (marked with a circle). The distances are estimated at the zeroth order in eccentricity110,111. For most systems, a single estimation of the generalized Laplace angle is made, whereas ref. 110 made an estimation for each Kepler quarter.

Extended Data Fig. 3 Observed distance from the equilibrium for all the simulated scenarios in which planets f and g continue the resonant chain.

The y axis is converted to the mean peak-to-peak amplitude from the generalized three-body Laplace angle using the following expression: mean \(({\mathcal{A}}({\varPsi }_{i}))=C/4\). Case A2 remains the one that has the potential to be the closest to an equilibrium.

Extended Data Fig. 4 Results from the ground-based campaign to detect HD 110067 f.

a, ΔWAIC for each of the constrained period bins when compared with a transit-free model. b,c, Best-fit decorrelated photometry with (b) and without (c) a transit model. Each light curve from each telescope has been offset for clarity. Error bars represent 1σ uncertainties.

Extended Data Fig. 5 Results from the two radial velocity analyses to measure the mass of each of the planets in the HD 110067 system.

Each histogram represents the posterior density function (pdf) of the radial velocity semiamplitudes as inferred from method I (red) and method II (blue). The area underneath each histogram is normalized to unity.

Extended Data Fig. 6 Gas mass fraction of the HD 110067 planets as a function of their equilibrium temperature.

We infer two values per planet by assuming the different planetary masses from our method I (red) and method II (blue) radial velocity analyses. The boxes, orange lines, green triangles and red stars represent, respectively, the 25th and 75th percentiles, medians, means and modes of the posterior distributions. The opacity of the vertical lines is proportional to the posterior distribution.

Extended Data Table 1 CHEOPS observing log
Extended Data Table 2 Ground-based photometric campaign observing log
Extended Data Table 3 Stellar parameters of HD 110067
Extended Data Table 4 Distance of the estimated generalized three-body Laplace angle Ψe=0 to the closest equilibrium for all period ratios that are not excluded by available observations

Supplementary information

Supplementary Information

The file includes Supplementary Figs. 1–12 and Supplementary Tables 1–5. The figures include: full detrended CHEOPS photometry of all visits (Fig. S1); high-resolution imaging of HD 110067 excluding nearby stellar companions (Fig. S2); potential orbital solutions from the analysis of the two duo transit and the two mono transit events (Fig. S3); properties of known resonant chains in terms of their period ratios (Fig. S4); a numerical integration of the best-fit solution of the full six-body resonant chain demonstrating the dynamical stability of the system (Fig. S5); original and reprocessed TESS Sector 23 data confirming the existence of planets f and g (Fig. S6); periodograms of the radial velocity and derived spectral indicators of the CARMENES and HARPS-N data (Figs. S7 and S8); best-fit solution of the radial velocity model from method I (Fig. S9); cross-validation analysis of the GP fit used in the radial velocity model from method II (Fig. S10); periodogram of radial velocity residuals after the fit demonstrating the absence of further signals in the data (Fig. S11); and corner plots of the most relevant parameters from the photometric fit (Fig. S12). The tables include the parameters, priors and posterior distributions of our photometric model (Table S1), radial velocity models using method I (Tables S2 and S3) and method II (Table S4), and internal structure model (Table S5).

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Luque, R., Osborn, H.P., Leleu, A. et al. A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067. Nature 623, 932–937 (2023). https://doi.org/10.1038/s41586-023-06692-3

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  • DOI: https://doi.org/10.1038/s41586-023-06692-3

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