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Six transiting planets and a chain of Laplace resonances in TOI-178

Leleu, A. ; Alibert, Y. ; Hara, N. C. ; Hooton, M. J. ; Wilson, T. G. ; Robutel, P. ; Delisle, J. B. ; Laskar, J. ; Hoyer, S. and Lovis, C. , et al. (2021) In Astronomy and Astrophysics 649.
Abstract

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... (More)

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+0.073to 2.87-0.13+0.14Earth 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+0.28to 0.177-0.061+0.055times 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.

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publication status
published
subject
keywords
Celestial mechanics, Planets and satellites: Detection, Planets and satellites: Dynamical evolution and stability, Techniques: Photometric, Techniques: Spectroscopic
in
Astronomy and Astrophysics
volume
649
article number
A26
publisher
EDP Sciences
external identifiers
  • scopus:85105617903
ISSN
0004-6361
DOI
10.1051/0004-6361/202039767
language
English
LU publication?
yes
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51094364-888a-4866-89ab-b20b3fe1c871
date added to LUP
2021-06-09 15:40:27
date last changed
2023-11-23 03:45:43
@article{51094364-888a-4866-89ab-b20b3fe1c871,
  abstract     = {{<p>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<sub>-0.070</sub><sup>+0.073</sup>to 2.87<sub>-0.13</sub><sup>+0.14</sup>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<sub>-0.23</sub><sup>+0.28</sup>to 0.177<sub>-0.061</sub><sup>+0.055</sup>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.</p>}},
  author       = {{Leleu, A. and Alibert, Y. and Hara, N. C. and Hooton, M. J. and Wilson, T. G. and Robutel, P. and Delisle, J. B. and Laskar, J. and Hoyer, S. and Lovis, C. and Bryant, E. M. and Ducrot, E. and Cabrera, J. and Delrez, L. and Acton, J. S. and Adibekyan, V. and Allart, R. and Allende Prieto, C. and Alonso, R. and Alves, D. and Anderson, D. R. and Angerhausen, D. and Anglada Escude&acute;, G. and Asquier, J. and Barrado, D. and Barros, S. C.C. and Baumjohann, W. and Bayliss, D. and Beck, M. and Beck, T. and Bekkelien, A. and Benz, W. and Billot, N. and Bonfanti, A. and Bonfils, X. and Bouchy, F. and Bourrier, V. and Boue&acute;, G. and Brandeker, A. and Broeg, C. and Buder, M. and Burdanov, A. and Burleigh, M. R. and Ba&acute;rczy, T. and Cameron, A. C. and Chamberlain, S. and Charnoz, S. and Cooke, B. F. and Corral Van Damme, C. and Correia, A. C.M. and Cristiani, S. and Damasso, M. and Davies, M. B. and Deleuil, M. and Demangeon, O. D.S. and Demory, B. O. and Di Marcantonio, P. and Di Persio, G. and Dumusque, X. and Ehrenreich, D. and Erikson, A. and Figueira, P. and Fortier, A. and Fossati, L. and Fridlund, M. and Futyan, D. and Gandolfi, D. and Garcia&acute; Muno&tild;z, A. and Garcia, L. J. and Gill, S. and Gillen, E. and Gillon, M. and Goad, M. R. and Gonza&acute;lez Herna&acute;ndez, J. I. and Guedel, M. and Gu&die;nther, M. N. and Haldemann, J. and Henderson, B. and Heng, K. and Hogan, A. E. and Isaak, K. and Jehin, E. and Jenkins, J. S. and Jorda&acute;n, A. and Kiss, L. and Kristiansen, M. H. and Lam, K. and Lavie, B. and Lecavelier Des Etangs, A. and Lendl, M. and Lillo-Box, J. and Lo Curto, G. and Magrin, D. and Martins, C. J.A.P. and Maxted, P. F.L. and McCormac, J. and Mehner, A. and Micela, G. and Molaro, P. and Moyano, M. and Murray, C. A. and Nascimbeni, V. and Nunes, N. J. and Olofsson, G. and Osborn, H. P. and Oshagh, M. and Ottensamer, R. and Pagano, I. and Palle&acute;, E. and Pedersen, P. P. and Pepe, F. A. and Persson, C. M. and Peter, G. and Piotto, G. and Polenta, G. and Pollacco, D. and Poretti, E. and Pozuelos, F. J. and Queloz, D. and Ragazzoni, R. and Rando, N. and Ratti, F. and Rauer, H. and Raynard, L. and Rebolo, R. and Reimers, C. and Ribas, I. and Santos, N. C. and Scandariato, G. and Schneider, J. and Sebastian, D. and Sestovic, M. and Simon, A. E. and Smith, A. M.S. and Sousa, S. G. and Sozzetti, A. and Steller, M. and Sua&acute;rez Mascareno&tild;, A. and Szabo&acute;, Gy M. and Se&acute;gransan, D. and Thomas, N. and Thompson, S. and Tilbrook, R. H. and Triaud, A. and Turner, O. and Udry, S. and Van Grootel, V. and Venus, H. and Verrecchia, F. and Vines, J. I. and Walton, N. A. and West, R. G. and Wheatley, P. J. and Wolter, D. and Zapatero Osorio, M. R.}},
  issn         = {{0004-6361}},
  keywords     = {{Celestial mechanics; Planets and satellites: Detection; Planets and satellites: Dynamical evolution and stability; Techniques: Photometric; Techniques: Spectroscopic}},
  language     = {{eng}},
  month        = {{05}},
  publisher    = {{EDP Sciences}},
  series       = {{Astronomy and Astrophysics}},
  title        = {{Six transiting planets and a chain of Laplace resonances in TOI-178}},
  url          = {{http://dx.doi.org/10.1051/0004-6361/202039767}},
  doi          = {{10.1051/0004-6361/202039767}},
  volume       = {{649}},
  year         = {{2021}},
}