Characterisation of the TOI-421 planetary system using CHEOPS, TESS, and archival radial velocity data
Journal article, 2024

Context. The TOI-421 planetary system contains two sub-Neptune-type planets (Pb ~ 5.2 days, Teqb ~ 900 K, and Pc ~ 16.1 days, Teq,c ~ 650 K) and is a prime target to study the formation and evolution of planets and their atmospheres. The inner planet is especially interesting as the existence of a hydrogen-dominated atmosphere at its orbital separation cannot be explained by current formation models without previous orbital migration. Aims. We aim to improve the system parameters to further use them to model the interior structure and simulate the atmospheric evolution of both planets, to finally gain insights into their formation and evolution. We also investigate the possibility of detecting transit timing variations (TTVs).
Methods. We jointly analysed photometric data of three TESS sectors and six CHEOPS visits as well as 156 radial velocity data points to retrieve improved planetary parameters. We also searched for TTVs and modelled the interior structure of the planets. Finally, we simulated the evolution of the primordial H-He atmospheres of the planets using two different modelling frameworks.
Results. We determine the planetary radii and masses of TOI-421 b and c to be Rb = 2.64 ± 0.08 R, Mb = 6.7 ± 0.6 M, Rc = 5.09 ± 0.07 R, and Mc = 14.1 ± 1.4 M. Using these results we retrieved average planetary densities of ρb = 0.37 ± 0.05ρ and ρc = 0.107 ± 0.012 ρ. We do not detect any statistically significant TTV signals. Assuming the presence of a hydrogen-dominated atmosphere, the interior structure modelling results in both planets having extensive envelopes. While the modelling of the atmospheric evolution predicts for TOI-421 b to have lost any primordial atmosphere that it could have accreted at its current orbital position, TOI-421 c could have started out with an initial atmospheric mass fraction somewhere between 10 and 35%.
Conclusions. We conclude that the low observed mean density of TOI-421 b can only be explained by either a bias in the measured planetary parameters (e.g. driven by high-altitude clouds) and/or in the context of orbital migration. We also find that the results of atmospheric evolution models are strongly dependent on the employed planetary structure model.

Planets and satellites: composition

Planets and satellites: fundamental parameters

Planets and satellites: individual: TOI-421

Author

A. Krenn

Institut fur Weltraumforschung

D. Kubyshkina

Institut fur Weltraumforschung

L. Fossati

Institut fur Weltraumforschung

J. A. Egger

University of Bern

A. Bonfanti

Institut fur Weltraumforschung

A. Deline

University of Geneva

D. Ehrenreich

University of Geneva

M. Beck

University of Geneva

W. Benz

University of Bern

J. Cabrera

German Aerospace Center (DLR)

T.G. Wilson

University of St Andrews

A. Leleu

University of Bern

University of Geneva

S.G. Sousa

University of Porto

V. Adibekyan

University of Porto

A. Correia

Centre for Physics of the University of Coimbra

Y. Alibert

University of Bern

L. Delrez

University of Liège

M. Lendl

University of Geneva

J. A. Patel

Stockholm University

J. Venturini

University of Geneva

R. Alonso

Instituto de Astrofísica de Canarias

University of La Laguna

G. Anglada

Institute of Space Studies of Catalonia (IEEC)

Institute of Space Sciences (ICE) - CSIC

J. Asquier

European Space Research and Technology Centre (ESA ESTEC)

T. Bárczy

Admatis

D. Barrado Navascues

European Space Astronomy Centre (ESAC)

S.C.C. Barros

University of Porto

W. Baumjohann

Institut fur Weltraumforschung

T. Beck

University of Bern

N. Billot

University of Geneva

X. Bonfils

Institut de Planétologie et d’Astrophysique de Grenoble (IPAG)

L. Borsato

Istituto nazionale di astrofisica (INAF)

A. Brandeker

Stockholm University

C. Broeg

University of Bern

S. Charnoz

Institut de Physique du Globe de Paris

A. Collier Cameron

University of St Andrews

Szilard Csizmadia

German Aerospace Center (DLR)

P. E. Cubillos

Istituto nazionale di astrofisica (INAF)

Institut fur Weltraumforschung

M. B. Davies

Lund University

M. Deleuil

Laboratoire d'Astrophysique de Marseille

O. Demangeon

University of Porto

B.O. Demory

University of Bern

Anders Erikson

German Aerospace Center (DLR)

A. Fortier

University of Bern

Malcolm Fridlund

Leiden University

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

D. Gandolfi

University of Turin

Michaël Gillon

University of Liège

M. Gudel

University of Vienna

Maximilian N. Günther

European Space Research and Technology Centre (ESA ESTEC)

J. Hasiba

Institut fur Weltraumforschung

A. Heitzmann

University of Geneva

Ch. Helling

Technische Universität Graz

Institut fur Weltraumforschung

S. Hoyer

Laboratoire d'Astrophysique de Marseille

K. Isaak

European Space Research and Technology Centre (ESA ESTEC)

L. L. Kiss

Eötvös Loránd University (ELTE)

Hungarian Academy of Sciences

K. W.F. Lam

German Aerospace Center (DLR)

J. Laskar

Paris Observatory

A. L. des Etangs

Centre national de la recherche scientifique (CNRS)

C. Lovis

University of Geneva

D. Magrin

Istituto nazionale di astrofisica (INAF)

P. Maxted

Keele University

C. Mordasini

University of Bern

Valerio Nascimbeni

Istituto nazionale di astrofisica (INAF)

G. Olofsson

Stockholm University

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)

Giampaolo P. Piotto

Istituto nazionale di astrofisica (INAF)

University of Padua

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 Research and Technology Centre (ESA ESTEC)

H. Rauer

Technische Universität Berlin

German Aerospace Center (DLR)

Freie Universität Berlin

I. Ribas

Institute of Space Sciences (ICE) - CSIC

Institute of Space Studies of Catalonia (IEEC)

M. Rieder

University of Bern

N. C. Santos

University of Porto

Gaetano Scandariato

Istituto nazionale di astrofisica (INAF)

D. Segransan

University of Geneva

A.E. Simon

University of Bern

A. M.S. Smith

German Aerospace Center (DLR)

M. Stalport

University of Liège

Manfred B. Steller

Institut fur Weltraumforschung

Gy M. Szabó

Eötvös Loránd University (ELTE)

Nicolas Thomas

University of Bern

S. Udry

University of Geneva

B. Ulmer

German Aerospace Center (DLR)

V. Van Grootel

University of Liège

E. Villaver

University of La Laguna

Instituto de Astrofísica de Canarias

V. Viotto

Istituto nazionale di astrofisica (INAF)

N. A. Walton

University of Cambridge

Tiziano Zingales

Istituto nazionale di astrofisica (INAF)

University of Padua

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 686 A301

Exoplanets from space -CHEOPS and PLATO ESA's next two projects (Phase 2)

Swedish National Space Board (65/19), 2020-01-01 -- 2022-12-31.

Swedish National Space Board (177/19), 2020-01-01 -- 2022-12-31.

Exoplanets from space – CHEOPS and PLATO, ESA’s next two projects

Swedish National Space Board (174/18), 2017-01-01 -- 2022-12-31.

Subject Categories

Meteorology and Atmospheric Sciences

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics

DOI

10.1051/0004-6361/202348584

More information

Latest update

7/26/2024