ASTEP confirmation of a pair of long-period Jupiter-sized planets with extremely low densities transiting TOI-791
Year: 2026
Type: article
Abstract: ABSTRACT Gas giant planets with periods $20~\lt ~P~\lt ~300~\rm d$ orbiting Sun-like stars are a relatively uncommon outcome of planetary formation, and key questions about the nature and formation of this subpopulation remain unanswered. Theoretical models for the location of their formation (in situ or ex situ) and for their subsequent migration predict different outcomes in terms of planet masses and eccentricities, indicating that observations have a key role to play in disentangling their histories. In this work, we present the discovery and confirmation of a pair of long-period Jupiter-sized planets transiting an F7 star: TOI-791 b is a $0.993\pm 0.033\rm ~R_{Jup}$ planet on a $139.29931_{-0.00012}^{+0.00011}~\rm d$ orbit, and TOI-791 c, a $1.155\pm 0.040\rm ~R_{Jup}$ planet on a $232.01570_{-0.00071}^{+0.00067}~\rm d$ orbit. The two planets are within 0.07 per cent of a second-order 5:3 period commensurability leading to transit timing variations (TTVs) of up to 50 min. We confirm their planetary nature using ground-based photometry, including multiple full detections of the $\gt 11~\rm h$ transits of both TOI-791 b and c from Antarctica with ASTEP, making these the longest-duration transits ever observed in their entirety from the ground. Our detailed analysis of the TTV signal allows us to measure dynamical masses for both planets, which yield densities of $\rho _{\rm b}=0.038\pm 0.008 \rm ~g~cm^{-3}$ and $\rho _{\rm c}=0.047\pm 0.006 \rm ~g~cm^{-3}$, indicating that TOI-791 b and c are two of the lowest density giant planets ever detected. While these measurements are robust, further follow-up is needed to fully characterize the TTV signal and the architecture of the system.
Authors: Georgina Dransfield, Antoine C Petit, Amaury H M J Triaud, Tristan Guillot, François-Xavier Schmider, Lyu Abe, Abdelkrim Agabi, Khalid Barkaoui, Thomas A Baycroft, Philippe Bendjoya, Rafael Brahm, Karen A Collins, Billy Edwards, Phil Evans, Alix V Freckelton, Nolan Grieves, Steve B Howell, Franco Mallia, Djamel Mekarnia, Angelica Psaridi, Daniel Sebastian, Keivan G Stassun, Chris Stockdale, Amalie Stokholm, Olga Suarez, Thiam-Guan Tan, Mathilde Timmermans, Cristilyn N Watkins, Carl Ziegler, Abderahmane Soubkiou, François Bouchy, Marion Cointepas, Vincent Deloupy, Maximilian N Günther, Michaël Gillon, Giovanni Isopi, Emmanuel Jehin, Jon M Jenkins, Andrés Jordán, Martin B Nielsen, Sara Seager, Avi Shporer, Julia V Seidel, Michal Steiner, Trifon Trifonov, Joseph D Twicken, Joshua N Winn, Aldo Zapparata
Institutions: University of Oxford, University of Birmingham, Centre National de la Recherche Scientifique, Université Côte d'Azur, Lagrange Laboratory, Observatoire de la Côte d’Azur, University of Liège, Instituto de Astrofísica de Canarias, Massachusetts Institute of Technology, Adolfo Ibáñez University, Millennium Institute of Astrophysics, Data Observatory Foundation, Center for Astrophysics Harvard & Smithsonian, Space Research Organisation Netherlands, Los Algarrobos Observatory, Lacombe Research and Development Centre, University of Geneva, Ames Research Center, Regione Lazio, Institute of Space Sciences, Consejo Superior de Investigaciones Científicas, Institut d'Estudis Espacials de Catalunya, Thüringer Landessternwarte Tautenburg, Vanderbilt University, Perth Exoplanet Survey Telescope Observatory, Stephen F. Austin State University, Institut de Planétologie et d'Astrophysique de Grenoble, Université Grenoble Alpes, European Space Agency, European Space Research and Technology Centre, University of Rome Tor Vergata, Istituto Nazionale di Fisica Nucleare, Sezione di Roma I, Sapienza University of Rome, National Institute for Astrophysics, European Southern Observatory, European Southern Observatory, Heidelberg University, Sofia University "St. Kliment Ohridski", Search for Extraterrestrial Intelligence, Princeton University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,046
Funders: National Science Foundation, National Aeronautics and Space Administration, California Institute of Technology, UK Research and Innovation, Healthcare Excellence Canada, European Commission, Agence Nationale de la Recherche, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Fonds De La Recherche Scientifique - FNRS, Institut Polaire Français Paul Emile Victor, Mitutoyo Association for Science and Technology, Agencia Nacional de Investigación y Desarrollo, National Academy of Sciences, Ames Research Center, Horizon 2020 Framework Programme, Science Mission Directorate, Science and Technology Facilities Council, H2020 European Research Council
Awards: INSTITUTO MILENIO DE ASTROFISICA, An upgrade to the mount of the ASTEP telescope, Red-enhanced cameras to seek rocky planets transiting Ultra-Cool Dwarfs, G3106129878, THE BULK AND ATMOSPHERIC COMPOSITION OF GIANT EXOPLANETS, G3648211085, G4126913923, G4252671623, G4276578120, G5278203998, G57481727, G5890451522, Temperate exoplanets from Chile & Antarctica, G7218776414, G7288031051, G7860760466, G8211471405, G8318038168, G8722425573, G8800819381, G880779785
OpenAlex ID: W7165871404