Characterization of two new transiting sub-Neptunes and a terrestrial planet around M-dwarf hosts

We report the confirmation of three transiting exoplanets orbiting TOI-1243 (LSPM J0902+7138), TOI-4529 (G 2-21), and TOI-5388 (Wolf 346) that were initially detected by TESS through ground-based photometry and radial velocity follow-up measurements with CARMENES. The planets present short orbital periods of 4.65, 5.88, and 2.59 days, and they orbit early-M dwarfs (M2.0 V, M1.5 V, and M3.0 V, respectively). We were able to precisely determine the radius of all three planets with a precision of <7%, the mass of TOI-1243 b with a precision of 19%, and upper mass limits for TOI-4529 b and TOI-5388 b. The radius of TOI-1243 b is 2.33 ± 0.12 R ⊕ , its mass is 7.7 ± 1.5 M ⊕ , and the mean density is 0.61 ± 0.15 ρ ⊕ . The radius of TOI-4529b is 1.77 −0.08 +0.09 R ⊕ , the 3 σ upper mass limit is 4.9 M ⊕ , and the 3 σ upper density limit is 0.88 ρ ⊕ . The third planet, TOI-5388 b, is Earth-sized with a radius of 0.99 −0.06 +0.07 R ⊕ , a 3 σ upper mass limit of 2.2 M ⊕ , and a 3 σ upper density limit of 2.2 ρ ⊕ . While TOI-5388 b is most probably rocky, given its Earth-like radius, TOI-1243 b and TOI-4529 b are located in a highly degenerate region in the mass-radius space. TOI-4529 b appears to lean toward a water-world composition. TOI-1243 b has enough mass to host a significant H-He envelope, although a water-world and pure rocky compositions are also consistent with the data. Our analysis indicates that future atmospheric observations using JWST can aid in determining their real composition. The sample of small planets around M dwarfs is widely used to understand planet formation and composition theories, and our study adds three planets to this sample.

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Journal
Astronomy and Astrophysics
Published
2026-01-12
DOI
https://doi.org/10.1051/0004-6361/202557155
Primary Topic
Stellar, planetary, and galactic studies
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article
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article

Characterization of two new transiting sub-Neptunes and a terrestrial planet around M-dwarf hosts

A. Reiners, Ismael Mireles, Ramotholo Sefako, S. Vanaverbeke et al.
Astronomy and Astrophysics
Stellar, planetary, and galactic studies
article

Characterization of two new transiting sub-Neptunes and a terrestrial planet around M-dwarf hosts

A. Reiners, Ismael Mireles, Ramotholo Sefako, S. Vanaverbeke, H. Parviainen, Andreas Quirrenbach, L. Tal-Or, G. Srdoc, I. Carleo, G. Covone, C. Cifuentes, G. Morello, A. Fukui, Y. Hayashi, Th. Henning, G. Fernández-Rodríguez, G. Lacedelli, F. Murgas, Y. Kawai, E. Esparza-Borges, E. Poultourtzidis, E. Herrero, E. Matthews, S. Geraldía-González, J. Orell-Miquel, K. Horne, E. Pallé, C. Magliano, S. Chairetas, K. Isogai, F. Libotte, Ignasi Ribas, F. Zong Lang
article en

Abstract

We report the confirmation of three transiting exoplanets orbiting TOI-1243 (LSPM J0902+7138), TOI-4529 (G 2-21), and TOI-5388 (Wolf 346) that were initially detected by TESS through ground-based photometry and radial velocity follow-up measurements with CARMENES. The planets present short orbital periods of 4.65, 5.88, and 2.59 days, and they orbit early-M dwarfs (M2.0 V, M1.5 V, and M3.0 V, respectively). We were able to precisely determine the radius of all three planets with a precision of <7%, the mass of TOI-1243 b with a precision of 19%, and upper mass limits for TOI-4529 b and TOI-5388 b. The radius of TOI-1243 b is 2.33 ± 0.12 R ⊕ , its mass is 7.7 ± 1.5 M ⊕ , and the mean density is 0.61 ± 0.15 ρ ⊕ . The radius of TOI-4529b is 1.77 −0.08 +0.09 R ⊕ , the 3 σ upper mass limit is 4.9 M ⊕ , and the 3 σ upper density limit is 0.88 ρ ⊕ . The third planet, TOI-5388 b, is Earth-sized with a radius of 0.99 −0.06 +0.07 R ⊕ , a 3 σ upper mass limit of 2.2 M ⊕ , and a 3 σ upper density limit of 2.2 ρ ⊕ . While TOI-5388 b is most probably rocky, given its Earth-like radius, TOI-1243 b and TOI-4529 b are located in a highly degenerate region in the mass-radius space. TOI-4529 b appears to lean toward a water-world composition. TOI-1243 b has enough mass to host a significant H-He envelope, although a water-world and pure rocky compositions are also consistent with the data. Our analysis indicates that future atmospheric observations using JWST can aid in determining their real composition. The sample of small planets around M dwarfs is widely used to understand planet formation and composition theories, and our study adds three planets to this sample.

Astronomy and AstrophysicsVol. 707
University of Bern (CH), Ames Research Center (US), Institute of Space Sciences (ES), University of Kansas (US), Universidad de La Laguna (ES), Tokyo University of the Arts (JP), University of New Mexico (US), Aristotle University of Thessaloniki (GR), Kyoto University (JP), Heidelberg University (DE), NASA Exoplanet Science Institute (US), Institute of Astrophysics and Space Sciences (PT), Institut d'Estudis Espacials de Catalunya (ES), Kavli Institute for Particle Astrophysics and Cosmology (US), Max Planck Institute for Astrophysics (DE), Osservatorio Astrofisico di Torino (IT), Istituto Nazionale di Fisica Nucleare, Sezione di Napoli (IT), Max Planck Institute for Astronomy (DE), Astrobiology Center (JP), South African Radio Astronomy Observatory (ZA), Centre of Plasma Physics - Institute for Plasma Research (IN), Center for Astrophysics Harvard & Smithsonian (US), Scottish Universities Physics Alliance (GB), Centro de Astrobiología (ES), Instituto de Astrofísica de Canarias (ES), Institute of Astronomy and Space Physics (AR), Thüringer Landessternwarte Tautenburg (DE), Astronomical Observatory (RS), Instituto de Astrofísica de Andalucía (ES), Stichting tot Steun VCVGZ (NL), Ariel University (IL), Massachusetts Institute of Technology (US), University of Naples Federico II (IT), The University of Tokyo (JP), The University of Texas at Austin (US), National Institute for Astrophysics (IT), Netherlands Institute for Radio Astronomy (NL)
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Stellar, planetary, and galactic studies
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