ASTEP confirmation of a pair of long-period Jupiter-sized planets with extremely low densities transiting TOI-791
Abstract
Gas giant planets with periods 20 lt P lt 300 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± 0.033~RJup planet on a 139.29931−0.00012+0.00011 d orbit, and TOI-791 c, a 1.155± 0.040~RJup planet on a 232.01570−0.00071+0.00067 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 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 ρ b=0.038± 0.008 ~g cm−3 and ρ c=0.047± 0.006 ~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.
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BibTeX
@article{dransfield2026astep,
title = {{ASTEP confirmation of a pair of long-period Jupiter-sized planets with extremely low densities transiting TOI-791}},
author = {Georgina Dransfield and Antoine Petit and Amaury Triaud and Tristan Guillot and François-Xavier Schmider and Lyu Abe and Abdelkrim Agabi and Khalid Barkaoui and Thomas Baycroft and Philippe Bendjoya and Rafael Brahm and Karen Collins and Billy Edwards and Phil Evans and Alix Freckelton and Nolan Grieves and Steve Howell and Franco Mallia and Djamel Mekarnia and Angelica Psaridi and Daniel Sebastian and Keivan Stassun and Chris Stockdale and Amalie Stokholm and Olga Suarez and Thiam-Guan Tan and Mathilde Timmermans and Cristilyn Watkins and Carl Ziegler and Abderahmane Soubkiou and François Bouchy and Marion Cointepas and Vincent Deloupy and Maximilian Günther and Michaël Gillon and Giovanni Isopi and Emmanuel Jehin and Jon Jenkins and Andrés Jordán and Martin Nielsen and Sara Seager and Avi Shporer and Julia Seidel and Michal Steiner and Trifon Trifonov and Joseph Twicken and Joshua Winn and Aldo Zapparata},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = jun,
doi = {10.1093/mnras/stag864},
eprint = {2606.30016},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05760264v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - ASTEP confirmation of a pair of long-period Jupiter-sized planets with extremely low densities transiting TOI-791
AU - Georgina Dransfield
AU - Antoine Petit
AU - Amaury Triaud
AU - Tristan Guillot
AU - François-Xavier Schmider
AU - Lyu Abe
AU - Abdelkrim Agabi
AU - Khalid Barkaoui
AU - Thomas Baycroft
AU - Philippe Bendjoya
AU - Rafael Brahm
AU - Karen Collins
AU - Billy Edwards
AU - Phil Evans
AU - Alix Freckelton
AU - Nolan Grieves
AU - Steve Howell
AU - Franco Mallia
AU - Djamel Mekarnia
AU - Angelica Psaridi
AU - Daniel Sebastian
AU - Keivan Stassun
AU - Chris Stockdale
AU - Amalie Stokholm
AU - Olga Suarez
AU - Thiam-Guan Tan
AU - Mathilde Timmermans
AU - Cristilyn Watkins
AU - Carl Ziegler
AU - Abderahmane Soubkiou
AU - François Bouchy
AU - Marion Cointepas
AU - Vincent Deloupy
AU - Maximilian Günther
AU - Michaël Gillon
AU - Giovanni Isopi
AU - Emmanuel Jehin
AU - Jon Jenkins
AU - Andrés Jordán
AU - Martin Nielsen
AU - Sara Seager
AU - Avi Shporer
AU - Julia Seidel
AU - Michal Steiner
AU - Trifon Trifonov
AU - Joseph Twicken
AU - Joshua Winn
AU - Aldo Zapparata
PY - 2026
DA - 2026/06/25
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag864
UR - https://hal.science/hal-05760264v1
AB - Gas giant planets with periods 20 lt P lt 300 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± 0.033~R_Jup planet on a 139.29931_−0.00012^+0.00011 d orbit, and TOI-791 c, a 1.155± 0.040~R_Jup planet on a 232.01570_−0.00071^+0.00067 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 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 ρ _b=0.038± 0.008 ~g cm^−3 and ρ _c=0.047± 0.006 ~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.
SN - 0035-8711
SN - 1365-2966
ER -