![Stability map of the TOI-2211 system in the (Ωc , Ic) plane for the outer planet candidate TOI-2211.02. All other orbital parameters were fixed to the nominal solution from Table A.4. The colour scale shows the adopted stability indicator, with blue regions corresponding to stable configurations and red regions to unstable configurations. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/10/Searching-for.png?fit=1200%2C675&ssl=1)
[astro-ph.EP] 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±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.
Mass-radius diagram showing the location of TOI-2211 b in relation to the known exoplanet population (data from the PlanetS catalogue; Otegi et al. 2020; Parc et al. 2024). In addition to TOI-2211 b, also TOI-238 b as presented in Paper I (Egger et al. 2025) is labelled. Also shown are a number of iso-composition curves generated using the BICEPS forward model (Haldemann et al. 2024) for TOI-2211 b’s equilibrium temperature. Planets that fall into the Hot Water World triangles are depicted with blue error bars, the Hot Water World triangle corresponding to the equilibrium temperature of TOI-2211 b is indicated in light blue. Markers of planets that fall into the triangle are colour-coded according to their equilibrium temperature. — [astro-ph.EP]
J. A. Egger, P. Cortés-Zuleta, D. Kubyshkina, H. P. Osborn, S. Marques, I. Crossfield, A. Deline, S. Ulmer-Moll, A. E. Simon, G. Scandariato, A. C. M. Correia, Y. N. E. Eschen, D. Gandolfi, V. Adibekyan, A. Bonfanti, C. Pezzotti, P. H. Premnath, S. G. Sousa, T. G. Wilson, L. Fossati, R. Eltschinger, Y. Alibert, D. Degen, G. Lacedelli, T. Zingales, B. Akinsanmi, R. Alonso, T. Bárczy, D. Barrado, S. C. C. Barros, W. Baumjohann, W. Benz, N. Billot, L. Borsato, A. Brandeker, C. Broeg, M. Buder, A. Castro-González, A. Collier Cameron, C. Corral Van Damme, Sz. Csizmadia, P. E. Cubillos, M. B. Davies, M. Deleuil, O. D. S. Demangeon, B.-O. Demory, A. Derekas, B. Edwards, D. Ehrenreich, A. Erikson, A. Fortier, M. Fridlund, K. Gazeas, M. Gillon, M. Güdel, M. N. Günther, J. Hasiba, A. Heitzmann, Ch. Helling, K. G. Isaak, L. L. Kiss, D. Kitzmann, J. Korth, K. W. F. Lam, J. Laskar, A. Lecavelier des Etangs, A. Leleu, M. Lendl, M. Lund, D. Magrin, P. F. L. Maxted, B. Merín, C. Mordasini, M. Munari, V. Nascimbeni, G. Olofsson, R. Ottensamer, I. Pagano, E. Pallé, A. Peel, G. Peter, D. Piazza, G. Piotto, D. Pollacco, D. Queloz, R. Ragazzoni, N. Rando, H. Rauer, I. Ribas, N. C. Santos, D. Ségransan, A. M. S. Smith, M. Stalport, S. Sulis, Gy. M. Szabó, S. Udry, V. Van Grootel, J. Venturini, E. Villaver, N. A. Walton, S. Wolf
Comments: 19 pages, 11 figures, accepted for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2610.08922 [astro-ph.EP] (or arXiv:2610.08922v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2610.08922
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Submission history
From: Jo Ann Egger
[v1] Tue, 6 Oct 2026 18:00:08 UTC (4,017 KB)
https://arxiv.org/abs/2610.08922
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