An ultra-short-period super-Earth and a sub-Neptune orbiting the K dwarf TOI-4311
Journal article, 2026
We report the discovery and characterization of the multiplanetary system around TOI-4311, a K dwarf kinematically between the Galactic thick disc and Hercules stream. TOI-4311 hosts an ultra-short-period super-Earth (P(Formula presented) 0.99 d, (Formula presented) R(Formula presented) ) and a longer period sub-Neptune (P(Formula presented) 15 d, (Formula presented) R(Formula presented) ) that was first detected in the Transiting Exoplanet Survey Satellite photometry. Using follow-up observations with CHaracterising ExOPlanet Satellite and High Accuracy Radial Velocity Planet Searcher (HARPS), we refine the planetary radius of both planets, derive the mass of planet b ((Formula presented) M(Formula presented) ), and confirm the planetary nature of planet c. Intriguingly, a third periodic signal is clearly detected in our HARPS Radial Velocities (RVs) that we cannot link to stellar activity. This signal could be attributed to a third planet (P(Formula presented) 38 d, Msin(i) = (Formula presented) M(Formula presented) ) in the system; however, with the current photometric data set we do not find a transit. Our dynamical analysis highlights that this potential outer planet would remain stable. Using the precise radius and mass for TOI-4311 b, we model its interior structure and find that it is very dense given the host star’s galactic kinematics and chemistry. Hence, this system could challenge current formation theories and provide insights into planet formation across the galaxy.
techniques: radial velocities
planets and satellites: detection
stars: individual: TOI-4311
planets and satellites: individual: TOI-4311 b & c
techniques: photometric
planets and satellites: interiors
Author
Yoshi Eschen
The University of Warwick
T.G. Wilson
The University of Warwick
A. Collier Cameron
University of St Andrews
A. J. Mustill
Lund University
J. A. Egger
European Space Agency (ESA)
S. Ulmer-Moll
Leiden University
University of Liège
D. Gandolfi
University of Turin
A. M.S. Smith
German Aerospace Center (DLR)
O. Demangeon
University of Porto
S.G. Sousa
University of Porto
A. Bonfanti
Institut fur Weltraumforschung
A. Correia
University of Coimbra
V. Adibekyan
University of Porto
G. Lacedelli
Instituto de Astrofísica de Canarias
University of La Laguna
A. Brandeker
Stockholm University
C. Pezzotti
University of Liège
B. Akinsanmi
University of Geneva
Y. Alibert
University of Bern
R. Alonso
University of La Laguna
Instituto de Astrofísica de Canarias
T. Bárczy
Admatis
D. Barrado
European Space Agency (ESA)
S.C.C. Barros
University of Porto
W. Baumjohann
Institut fur Weltraumforschung
W. Benz
University of Bern
N. Billot
University of Geneva
L. Borsato
Istituto nazionale di astrofisica (INAF)
C. Broeg
University of Bern
A. Castro-González
University of Geneva
Szilard Csizmadia
German Aerospace Center (DLR)
P. E. Cubillos
Institut fur Weltraumforschung
Istituto nazionale di astrofisica (INAF)
Melvyn B. Davies
Lund University
M. Deleuil
Laboratoire d'Astrophysique de Marseille
A. Deline
University of Geneva
B.O. Demory
University of Bern
A. Derekas
Eötvös Loránd University (ELTE)
G. Di Persio
Istituto nazionale di astrofisica (INAF)
Billy Edwards
Netherlands Institute for Space Research (SRON)
D. Ehrenreich
University of Geneva
Anders Erikson
German Aerospace Center (DLR)
A. Fortier
University of Bern
L. Fossati
Institut fur Weltraumforschung
Malcolm Fridlund
Leiden University
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
K. Gazeas
University of Athens
Michaël Gillon
University of Liège
M. Gudel
University of Vienna
Maximilian N. Günther
European Space Agency (ESA)
A. Heitzmann
University of Geneva
Ch. Helling
Technische Universität Graz
Institut fur Weltraumforschung
K. Isaak
European Space Agency (ESA)
Jon M. Jenkins
National Aeronautics and Space Administration (NASA)
Tatiana Keller
University of Bern
L. L. Kiss
Eötvös Loránd University (ELTE)
Hungarian Academy of Sciences
D. Kitzmann
University of Bern
Judith Korth
University of Geneva
K. W.F. Lam
German Aerospace Center (DLR)
J. Laskar
Paris Observatory
A. L. des Etangs
Institut d 'Astrophysique de Paris
A. Leleu
University of Geneva
University of Bern
M. Lendl
University of Geneva
D. Magrin
Istituto nazionale di astrofisica (INAF)
P. Maxted
Keele University
Bruno Merín
European Space Agency (ESA)
C. Mordasini
University of Bern
Valerio Nascimbeni
Istituto nazionale di astrofisica (INAF)
G. Olofsson
Stockholm University
H. P. Osborn
Swiss Federal Institute of Technology in Zürich (ETH)
University of Bern
R. Ottensamer
University of Vienna
I. Pagano
Istituto nazionale di astrofisica (INAF)
Enric Palle
Instituto de Astrofísica de Canarias
University of La Laguna
G. Peter
German Aerospace Center (DLR)
G. Petitpas
Massachusetts Institute of Technology (MIT)
D. Piazza
University of Bern
Giampaolo P. Piotto
University of Padua
Istituto nazionale di astrofisica (INAF)
Don L. Pollacco
The University of Warwick
D. Queloz
Swiss Federal Institute of Technology in Zürich (ETH)
University of Cambridge
Roberto Ragazzoni
Istituto nazionale di astrofisica (INAF)
University of Padua
N. Rando
European Space Agency (ESA)
H. Rauer
German Aerospace Center (DLR)
Freie Universität Berlin
I. Ribas
Spanish National Research Council (CSIC)
Centre Tecnològic de Telecomunicacions de Catalunya (CTTC)
N. C. Santos
University of Porto
Gaetano Scandariato
Istituto nazionale di astrofisica (INAF)
D. Segransan
University of Geneva
Avi Shporer
Massachusetts Institute of Technology (MIT)
André M. Silva
University of Porto
A.E. Simon
University of Bern
R. Southworth
European Space Agency (ESA)
M. Stalport
University of Liège
S. Sulis
Laboratoire d'Astrophysique de Marseille
G.M. Szabó
Eötvös Loránd University (ELTE)
S. Udry
University of Geneva
B. Ulmer
German Aerospace Center (DLR)
V. Van Grootel
University of Liège
J. Venturini
University of Geneva
E. Villaver
University of La Laguna
Instituto de Astrofísica de Canarias
N. A. Walton
University of Cambridge
S. Wolf
University of Bern
C. Ziegler
Stephen F. Austin State University
Tiziano Zingales
Istituto nazionale di astrofisica (INAF)
University of Padua
Monthly Notices of the Royal Astronomical Society
0035-8711 (ISSN) 1365-2966 (eISSN)
Vol. 549 3 stag952Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
DOI
10.1093/mnras/stag952