techniques: photometric; techniques: spectroscopic; celestial mechanics; planets and satellites: detection; planets and satellites: dynamical evolution and stability; Astrophysics - Earth and Planetary Astrophysics
Abstract :
[en] Determining the architecture of multi-planetary systems is one of the cornerstones of understanding planet formation and evolution. Resonant systems are especially important as the fragility of their orbital configuration ensures that no significant scattering or collisional event has taken place since the earliest formation phase when the parent protoplanetary disc was still present. In this context, TOI-178 has been the subject of particular attention since the first TESS observations hinted at the possible presence of a near 2:3:3 resonant chain. Here we report the results of observations from CHEOPS, ESPRESSO, NGTS, and SPECULOOS with the aim of deciphering the peculiar orbital architecture of the system. We show that TOI-178 harbours at least six planets in the super-Earth to mini-Neptune regimes, with radii ranging from 1.152‒0.070+0.073 to 2.87‒0.13+0.14 Earth radii and periods of 1.91, 3.24, 6.56, 9.96, 15.23, and 20.71 days. All planets but the innermost one form a 2:4:6:9:12 chain of Laplace resonances, and the planetary densities show important variations from planet to planet, jumping from 1.02‒0.23+0.28 to 0.177‒0.061+0.055 times the Earth's density between planets c and d. Using Bayesian interior structure retrieval models, we show that the amount of gas in the planets does not vary in a monotonous way, contrary to what one would expect from simple formation and evolution models and unlike other known systems in a chain of Laplace resonances. The brightness of TOI-178 (H = 8.76 mag, J = 9.37 mag, V = 11.95 mag) allows for a precise characterisation of its orbital architecture as well as of the physical nature of the six presently known transiting planets it harbours. The peculiar orbital configuration and the diversity in average density among the planets in the system will enable the study of interior planetary structures and atmospheric evolution, providing important clues on the formation of super-Earths and mini-Neptunes.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Leleu, A.; Observatoire Astronomique de l'Université de Genève, Chemin Pegasi 51, Versoix, Switzerland
Alibert, Y.; Physikalisches Institut, University of Bern, Gesellsschaftstrasse 6, 3012, Bern, Switzerland
Hara, N. C.; Observatoire Astronomique de l'Université de Genève, Chemin Pegasi 51, Versoix, Switzerland
Hooton, M. J.; Physikalisches Institut, University of Bern, Gesellsschaftstrasse 6, 3012, Bern, Switzerland
Wilson, T. G.; Centre for Exoplanet Science, SUPA School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, KY16 9SS, UK
Robutel, P.; IMCCE, UMR8028 CNRS, Observatoire de Paris, PSL Univ., Sorbonne Univ., 77 av. Denfert-Rochereau, 75014, Paris, France
Delisle, J.-B.; Observatoire Astronomique de l'Université de Genève, Chemin Pegasi 51, Versoix, Switzerland
Laskar, J.; IMCCE, UMR8028 CNRS, Observatoire de Paris, PSL Univ., Sorbonne Univ., 77 av. Denfert-Rochereau, 75014, Paris, France
Hoyer, S.; Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
Lovis, C.; Observatoire Astronomique de l'Université de Genève, Chemin Pegasi 51, Versoix, Switzerland
Bryant, E. M.; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
Murray, C. A.; Cavendish Laboratory, JJ Thomson Avenue, Cambridge, CB3 0HE, UK
Tilbrook, R. H.; School of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
Triaud, A.; School of Physics & Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
Turner, O.; Observatoire Astronomique de l'Université de Genève, Chemin Pegasi 51, Versoix, Switzerland
Udry, S.; Observatoire Astronomique de l'Université de Genève, Chemin Pegasi 51, Versoix, Switzerland
Van Grootel, Valérie ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astrophysique stellaire théorique et astérosismologie
Venus, H.; Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489, Berlin, Germany
Verrecchia, F.; Space Science Data Center, ASI, via del Politecnico snc, 00133, Roma, Italy
Vines, J. I.; Camino El Observatorio 1515, Las Condes, Santiago, Chile
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Walton, N. A.; Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
West, R. G.; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
Wheatley, P. J.; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
Wolter, D.; Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489, Berlin, Germany
Zapatero Osorio, M. R.; Centro de Astrobiología (CSIC-INTA), Crta. Ajalvir km 4, 28850, Torrejón de Ardoz, Madrid, Spain)
Allart, R.; Observatoire Astronomique de l'Université de Genève, Chemin Pegasi 51, Versoix, Switzerland
Allende Prieto, C.; Instituto de Astrofísica de Canarias, 38200, La Laguna, Tenerife, Spain
Alonso, R.; Instituto de Astrofísica de Canarias, 38200, La Laguna, Tenerife, Spain
Alves, D.; Camino El Observatorio 1515, Las Condes, Santiago, Chile
Anderson, D. R.; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
Angerhausen, D.; ETH Zürich, Institute for Particle Physics and Astrophysics, Zurich, Switzerland
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Baumjohann, W.; Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042, Graz, Austria
Bayliss, D.; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
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Beck, T.; Physikalisches Institut, University of Bern, Gesellsschaftstrasse 6, 3012, Bern, Switzerland
Bekkelien, A.; Observatoire Astronomique de l'Université de Genève, Chemin Pegasi 51, Versoix, Switzerland
Benz, W.; Physikalisches Institut, University of Bern, Gesellsschaftstrasse 6, 3012, Bern, Switzerland
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Broeg, C.; Physikalisches Institut, University of Bern, Gesellsschaftstrasse 6, 3012, Bern, Switzerland
Buder, M.; Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489, Berlin, Germany
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Burleigh, M. R.; School of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
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Cameron, A. C.; Centre for Exoplanet Science, SUPA School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, KY16 9SS, UK
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Charnoz, S.; Université de Paris, Institut de physique du globe de Paris, CNRS, 75005, Paris, France
Cooke, B. F.; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
Corral Van Damme, C.; ESTEC, European Space Agency, 2201AZ, Noordwijk, The Netherlands
Correia, A. C. M.; CFisUC, Department of Physics, University of Coimbra, 3004-516, Coimbra, Portugal
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Deleuil, M.; Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
Demangeon, O. D. S.; Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762, Porto, Portugal
Demory, B.-O.; Center for Space and Habitability, Gesellsschaftstrasse 6, 3012, Bern, Switzerland
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Dumusque, X.; Observatoire Astronomique de l'Université de Genève, Chemin Pegasi 51, Versoix, Switzerland
Ehrenreich, D.; Observatoire Astronomique de l'Université de Genève, Chemin Pegasi 51, Versoix, Switzerland
Erikson, A.; Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489, Berlin, Germany
Figueira, P.; Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762, Porto, Portugal
Fortier, A.; Physikalisches Institut, University of Bern, Gesellsschaftstrasse 6, 3012, Bern, Switzerland
Fossati, L.; Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042, Graz, Austria
Fridlund, M.; Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA, Leiden, The Netherlands
Futyan, D.; Observatoire Astronomique de l'Université de Genève, Chemin Pegasi 51, Versoix, Switzerland
Gandolfi, D.; Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, 10125, Torino, Italy
García Muñoz, A.; Center for Astronomy and Astrophysics, Technical University Berlin, Hardenberstrasse 36, 10623, Berlin, Germany
Garcia, Lionel ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Exotic
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Gillen, E.; Astronomy Unit, Queen Mary University of London, Mile End Road, London, E1 4NS, UK
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Goad, M. R.; School of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
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Guedel, M.; University of Vienna, Department of Astrophysics, Türkenschanzstrasse 17, 1180, Vienna, Austria
Günther, M. N.; Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
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Henderson, B.; School of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
Heng, K.; Center for Space and Habitability, Gesellsschaftstrasse 6, 3012, Bern, Switzerland
Hogan, A. E.; School of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
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