Searching for hot water world candidates with CHEOPS: II. A low-density super-Earth orbiting the K dwarf TOI-2211
Abstract
Small exoplanets on close-in orbits are exposed to high levels of stellar irradiation, which can effectively remove low-mass primordial H/He envelopes through atmospheric escape. Under these conditions, planets whose masses and radii are incompatible with both bare rocky interiors and extended H-dominated atmospheres are therefore expected to host high mean molecular weight atmospheres, making them promising candidates for volatile-rich hot water worlds. We present the first detailed characterisation of the low-density super-Earth TOI-2211 b (P~3.09 d), a recently validated transiting planet orbiting a K type star (G mag: 9.1). Combining TESS and CHEOPS photometry with radial velocity measurements from HARPS, ESPRESSO, and KPF, we precisely constrain the planet's radius and mass to 1.457 ± 0.047 R⊕ and 2.69 ± 0.56 M⊕. We also identify an outer, non-transiting planetary candidate (P~15.6 d, Msin(i) $ = 8.53 \pm 1.04$ M⊕) in the radial velocity data. We investigate the internal structure of the transiting planet and assess the stability of the inferred volatile envelopes through a detailed evaporation analysis, thereby identifying TOI-2211 b as a promising hot water world candidate. TOI-2211 b therefore joins the small but growing sample of these close-in low-density super-Earths, which represent particularly interesting targets for testing current planet formation and evolution theories. Additionally, we investigate the full architecture of the planetary system using a generative model of planet formation and evolution, with the resulting posterior distributions showing a clear over-density consistent with the observed orbital period and minimal mass of the non-transiting planetary candidate identified in the radial velocity data.
Related
- Searching for Black Hole Candidates in Quiescence by Using Multiband Observations in Globular Cluster M22 (NGC 6656)
- Searching for substellar companion candidates with Gaia. V. M dwarfs within 15 pc studied with absolute astrometry, radial velocities, and direct imaging
- Gravitational wave signals from primordial black holes orbiting solar-type stars
- Helium escaping from the atmosphere of a nearby rocky exoplanet orbiting in a habitable zone
- Dissecting the variability of Sagittarius A* in the orbiting hotspot framework
BibTeX
@misc{egger2026searching,
title = {{Searching for hot water world candidates with CHEOPS: II. A low-density super-Earth orbiting the K dwarf TOI-2211}},
author = {J. A. Egger and P. Cortés-Zuleta and D. Kubyshkina and H. P. Osborn and S. Marques and I. Crossfield and A. Deline and S. Ulmer-Moll and A. E. Simon and G. Scandariato and A. C. M. Correia and Y. N. E. Eschen and D. Gandolfi and V. Adibekyan and A. Bonfanti and C. Pezzotti and P. H. Premnath and S. G. Sousa and T. G. Wilson and L. Fossati and R. Eltschinger and Y. Alibert and D. Degen and G. Lacedelli and T. Zingales and B. Akinsanmi and R. Alonso and T. Bárczy and D. Barrado and S. C. C. Barros and W. Baumjohann and W. Benz and N. Billot and L. Borsato and A. Brandeker and C. Broeg and M. Buder and A. Castro-González and A. Collier Cameron and C. Corral Van Damme and Sz. Csizmadia and P. E. Cubillos and M. B. Davies and M. Deleuil and O. D. S. Demangeon and B. -O. Demory and A. Derekas and B. Edwards and D. Ehrenreich and A. Erikson and A. Fortier and M. Fridlund and K. Gazeas and M. Gillon and M. Güdel and M. N. Günther and J. Hasiba and A. Heitzmann and Ch. Helling and K. G. Isaak},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.08922},
eprint = {2610.08922},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.08922},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Searching for hot water world candidates with CHEOPS: II. A low-density super-Earth orbiting the K dwarf TOI-2211
AU - J. A. Egger
AU - P. Cortés-Zuleta
AU - D. Kubyshkina
AU - H. P. Osborn
AU - S. Marques
AU - I. Crossfield
AU - A. Deline
AU - S. Ulmer-Moll
AU - A. E. Simon
AU - G. Scandariato
AU - A. C. M. Correia
AU - Y. N. E. Eschen
AU - D. Gandolfi
AU - V. Adibekyan
AU - A. Bonfanti
AU - C. Pezzotti
AU - P. H. Premnath
AU - S. G. Sousa
AU - T. G. Wilson
AU - L. Fossati
AU - R. Eltschinger
AU - Y. Alibert
AU - D. Degen
AU - G. Lacedelli
AU - T. Zingales
AU - B. Akinsanmi
AU - R. Alonso
AU - T. Bárczy
AU - D. Barrado
AU - S. C. C. Barros
AU - W. Baumjohann
AU - W. Benz
AU - N. Billot
AU - L. Borsato
AU - A. Brandeker
AU - C. Broeg
AU - M. Buder
AU - A. Castro-González
AU - A. Collier Cameron
AU - C. Corral Van Damme
AU - Sz. Csizmadia
AU - P. E. Cubillos
AU - M. B. Davies
AU - M. Deleuil
AU - O. D. S. Demangeon
AU - B. -O. Demory
AU - A. Derekas
AU - B. Edwards
AU - D. Ehrenreich
AU - A. Erikson
AU - A. Fortier
AU - M. Fridlund
AU - K. Gazeas
AU - M. Gillon
AU - M. Güdel
AU - M. N. Günther
AU - J. Hasiba
AU - A. Heitzmann
AU - Ch. Helling
AU - K. G. Isaak
PY - 2026
DA - 2026/10/06
PB - arXiv
DO - 10.48550/arxiv.2610.08922
UR - https://arxiv.org/abs/2610.08922
AB - Small exoplanets on close-in orbits are exposed to high levels of stellar irradiation, which can effectively remove low-mass primordial H/He envelopes through atmospheric escape. Under these conditions, planets whose masses and radii are incompatible with both bare rocky interiors and extended H-dominated atmospheres are therefore expected to host high mean molecular weight atmospheres, making them promising candidates for volatile-rich hot water worlds. We present the first detailed characterisation of the low-density super-Earth TOI-2211 b (P~3.09 d), a recently validated transiting planet orbiting a K type star (G mag: 9.1). Combining TESS and CHEOPS photometry with radial velocity measurements from HARPS, ESPRESSO, and KPF, we precisely constrain the planet's radius and mass to 1.457 ± 0.047 R_⊕ and 2.69 ± 0.56 M_⊕. We also identify an outer, non-transiting planetary candidate (P~15.6 d, Msin(i) $ = 8.53 \pm 1.04$ M_⊕) in the radial velocity data. We investigate the internal structure of the transiting planet and assess the stability of the inferred volatile envelopes through a detailed evaporation analysis, thereby identifying TOI-2211 b as a promising hot water world candidate. TOI-2211 b therefore joins the small but growing sample of these close-in low-density super-Earths, which represent particularly interesting targets for testing current planet formation and evolution theories. Additionally, we investigate the full architecture of the planetary system using a generative model of planet formation and evolution, with the resulting posterior distributions showing a clear over-density consistent with the observed orbital period and minimal mass of the non-transiting planetary candidate identified in the radial velocity data.
ER -