TOI-283 b: A Transiting Mini-Neptune In A 17.6-day Orbit Discovered With TESS And ESPRESSO

Super-Earths and mini-Neptunes are missing from our Solar System, yet they appear to be the most abundant planetary types in our Galaxy.

A detailed characterization of key planets within this population is important for understanding the formation mechanisms of rocky and gas giant planets and the diversity of planetary interior structures. In 2019, NASA’s TESS satellite found a transiting planet candidate in a 17.6-day orbit around the star TOI-283.

We started radial velocity (RV) follow-up observations with ESPRESSO to obtain a mass measurement. Mass and radius are measurements critical for planetary classification and internal composition modeling. We used ESPRESSO spectra to derive the stellar parameters of the planet candidate host star TOI-283. We then performed a joint analysis of the photometric and RV data of this star, using Gaussian processes to model the systematic noise present in both datasets.

We find that the host is a bright K-type star (d=82.4 pc, T_eff=5213±70 K, V=10.4 mag) with a mass and radius of M_⋆=0.80±0.01M_⊙ and R_⋆=0.85±0.03R_⊙. The planet has an orbital period of P=17.617 days, a size of R_p=2.34±0.09R_⊕, and a mass of M_p=6.54±2.04M⊕. With an equilibrium temperature of ∼600 K and a bulk density of ρp=2.81±0.93 g cm⁻³, this planet is positioned in the mass-radius diagram where planetary models predict H₂O- and H/He-rich envelopes.

The ESPRESSO RV data also reveal a long-term trend that is probably related to the star’s activity cycle. Further RV observations are required to confirm whether this signal originates from stellar activity or another planetary body in the system.

F. Murgas, E. Pallé, A. Suárez Mascareño, J. Korth, F. J. Pozuelos, M. J. Hobson, B. Lavie, C. Lovis, S. G. Sousa, D. Bossini, H. Parviainen, A. Castro-González, V. Adibekyan, C. Allende Prieto, Y. Alibert, F. Bouchy, C. Briceño, D. A. Caldwell, D. Ciardi, C. Clark, K. A. Collins, K. I. Collins, S. Cristiani, X. Dumusque, D. Ehrenreich, P. Figueira, E. Furlan, R. Génova Santos, C. Gnilka, J. I. González Hernández, Z. Hartman, S. B. Howell, J. M. Jenkins, N. Law, C. Littlefield, G. Lo Curto, A. W. Mann, C. J. A. P. Martins, A. Mehner, G. Micela, P. Molaro, N. J. Nunes, F. Pepe, R. Rebolo, H. M. Relles, N. C. Santos, N. J. Scott, S. Seager, A. Sozzetti, S. Udry, C. N. Watkins, J. N. Winn, M. R. Zapatero Osorio, C. Ziegler

Comments: Accepted for publication in A&A, 25 pages, 20 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2510.15084 [astro-ph.EP] (or arXiv:2510.15084v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2510.15084
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Submission history
From: Felipe Murgas
[v1] Thu, 16 Oct 2025 18:59:42 UTC (7,872 KB)
https://arxiv.org/abs/2510.15084

Astrobiology, Exoplanet,