Searching for hot water world candidates with CHEOPS: Refining the radii and analysing the internal structures and atmospheric lifetimes of TOI-238 b and TOI-1685 b
Artikel i vetenskaplig tidskrift, 2025
Studying the composition of exoplanets is one of the most promising approaches to observationally constrain planet formation and evolution processes. However, this endeavour is complicated for small exoplanets by the fact that a wide range of compositions are compatible with their observed bulk properties. To overcome this issue, we identify triangular regions in the mass-radius space where part of this intrinsic degeneracy is lifted for close-in planets, since low-mass H/He envelopes would not be stable due to high-energy stellar irradiation. Planets in these Hot Water World triangles need to contain at least some heavier volatiles and are therefore interesting targets for atmospheric follow-up observations. We perform a demographic study to show that only few well-characterised planets in these regions are currently known and introduce our CHEOPS GTO programme aimed at identifying more of these potential hot water worlds. Here, we present CHEOPS observations for the first two targets of our programme, TOI-238 b and TOI-1685 b. Combined with TESS photometry and published RVs, we use the precise radii and masses of both planets to study their location relative to the corresponding Hot Water World triangles, perform an interior structure analysis, and study the possible lifetimes of H/He and waterdominated atmospheres under these conditions. We find that TOI-238 blies, at the 1σ level, inside the corresponding triangle. While a pure H/He atmosphere would have evaporated after 0.4-1.3 Myr, it is likely that a water-dominated atmosphere would have survived until the current age of the system, which makes TOI-238 ba promising candidate for a hot water world. Conversely, TOI-1685 b lies below the mass-radius model for a pure silicate planet, meaning that even though a water-dominated atmosphere would be compatible both with our internal structure and evaporation analysis, we cannot rule out the planet being a bare core.
Planets and satellites: individual: TOI-238
Techniques: photometric
Planets and satellites: individual: TOI-1685
Planets and satellites: interiors
Planets and satellites: formation
Författare
J. A. Egger
Universität Bern
D. Kubyshkina
Institut fur Weltraumforschung
Universität Bern
Y. Alibert
Universität Bern
H. P. Osborn
Eidgenössische Technische Hochschule Zürich (ETH)
Universität Bern
A. Bonfanti
Institut fur Weltraumforschung
T.G. Wilson
The University of Warwick
A. Brandeker
Stockholms universitet
Maximilian N. Günther
Europeiska rymdorganisationen (ESA)
M. Lendl
Université de Genève
D. Kitzmann
Universität Bern
L. Fossati
Institut fur Weltraumforschung
C. Mordasini
Universität Bern
S.G. Sousa
Universidade do Porto
V. Adibekyan
Universidade do Porto
Malcolm Fridlund
Universiteit Leiden
Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik
C. Pezzotti
Universite de Liège
D. Gandolfi
Universita degli Studi di Torino
S. Ulmer-Moll
Universite de Liège
Université de Genève
Universität Bern
R. Alonso
Universidad de la Laguna
Instituto de Astrofísica de Canarias
T. Bárczy
Admatis
D. Barrado Navascues
Europeiska rymdorganisationen (ESA)
S.C.C. Barros
Universidade do Porto
W. Baumjohann
Institut fur Weltraumforschung
W. Benz
Universität Bern
N. Billot
Université de Genève
L. Borsato
Istituto nazionale di astrofisica (INAF)
C. Broeg
Universität Bern
A. Collier Cameron
University of St Andrews
A. Correia
Universidade de Coimbra
Szilard Csizmadia
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
P. E. Cubillos
Istituto nazionale di astrofisica (INAF)
Institut fur Weltraumforschung
Melvyn B. Davies
Lunds universitet
M. Deleuil
Laboratoire d'Astrophysique de Marseille
A. Deline
Université de Genève
O. Demangeon
Universidade do Porto
B.O. Demory
Universität Bern
A. Derekas
Eötvös Loránd University (ELTE)
Billy Edwards
Netherlands Institute for Space Research (SRON)
D. Ehrenreich
Université de Genève
Anders Erikson
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
A. Fortier
Universität Bern
K. Gazeas
University of Athens
Michaël Gillon
Universite de Liège
M. Gudel
Universität Wien
A. Heitzmann
Université de Genève
Ch. Helling
Technische Universität Graz
Institut fur Weltraumforschung
K. Isaak
Europeiska rymdorganisationen (ESA)
L. L. Kiss
Magyar Tudomanyos Akademia
Eötvös Loránd University (ELTE)
Judith Korth
Lunds universitet
K. W.F. Lam
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
J. Laskar
Observatoire de Paris
A. L. des Etangs
Institut d 'Astrophysique de Paris
A. Luntzer
Universität Wien
R. Luque
University of Chicago
D. Magrin
Istituto nazionale di astrofisica (INAF)
P. Maxted
Keele University
Bruno Merín
Europeiska rymdorganisationen (ESA)
M. Munari
Istituto nazionale di astrofisica (INAF)
Valerio Nascimbeni
Istituto nazionale di astrofisica (INAF)
G. Olofsson
Stockholms universitet
R. Ottensamer
Universität Wien
I. Pagano
Istituto nazionale di astrofisica (INAF)
Enric Palle
Universidad de la Laguna
Instituto de Astrofísica de Canarias
G. Peter
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
D. Piazza
Universität Bern
Giampaolo P. Piotto
Università di Padova
Istituto nazionale di astrofisica (INAF)
Don L. Pollacco
The University of Warwick
D. Queloz
University of Cambridge
Eidgenössische Technische Hochschule Zürich (ETH)
R. Ragazzoni
Università di Padova
Istituto nazionale di astrofisica (INAF)
N. Rando
Europeiska rymdorganisationen (ESA)
H. Rauer
Freie Universität Berlin
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
I. Ribas
Centre Tecnològic de Telecomunicacions de Catalunya (CTTC)
Consejo Superior de Investigaciones Científicas (CSIC)
N. C. Santos
Universidade do Porto
Gaetano Scandariato
Istituto nazionale di astrofisica (INAF)
D. Segransan
Université de Genève
A.E. Simon
Universität Bern
A. M.S. Smith
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
R. Southworth
Europeiska rymdorganisationen (ESA)
M. Stalport
Universite de Liège
S. Sulis
Laboratoire d'Astrophysique de Marseille
G.M. Szabó
Eötvös Loránd University (ELTE)
S. Udry
Université de Genève
V. Van Grootel
Universite de Liège
J. Venturini
Université de Genève
E. Villaver
Instituto de Astrofísica de Canarias
Universidad de la Laguna
N. A. Walton
University of Cambridge
S. Wolf
Universität Bern
D. Wolter
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 696 A28Ämneskategorier (SSIF 2025)
Astronomi, astrofysik och kosmologi
DOI
10.1051/0004-6361/202453325