Multicolour Validation Of Two Temperate Mini-Neptunes Around M-dwarf Habitable Zones

For small planets orbiting within the habitable zones of their host stars, multicolour validation via photometric transit observations offers an efficient alternative to prioritize targets before intensive radial-velocity follow-up, thereby expanding the sample of habitable-zone exoplanets amenable for atmospheric characterisation.

In this study, we validate two exceptional habitable-zone TESS candidates, orbiting around M-dwarfs, as genuine planets, precisely determining their transit and physical parameters. We perform Bayesian model comparison by jointly fitting multicolour light curves from TESS and ground-based follow-up, including observations with HiPERCAM at the 10.4-m GTC.

Our approach uses wavelength-dependent transit depth variations and precise transit geometry to reject false positives. We validate TOI-2094 b and TOI-7166 b as two new benchmark temperate mini-Neptunes. TOI-2094 b (1.90 R_⊕) orbits its M3V star with a period of ∼18.79 days, well within the habitable zone (∼0.98 Earth insolation).

TOI-7166 b (2.39 R_⊕) orbits its M4.5V host star with a period of ∼12.92 days, placing it near the inner edge of the habitable zone (∼1.93 Earth insolation). Statistical mass and density estimates suggest that TOI-2094 b may be a volatile-rich planet, such as a water world or a gaseous planet, and is less likely to be rocky, while TOI-7166 b is likely to be volatile-rich.

Both planets are of great interest for detailed atmospheric characterisation with the JWST and future ELTs, which requires further precise mass measurements.

Transiting exoplanets of 0.5–4 Earth radii around habitable zones with TSM greater than 10. The error bars with square markers are confirmed or validated planets. The coloured dots are TESS candidates from the ExoFOP database. The colour of each marker indicates the TSM defined in Kempton et al. (2018). The green shaded area is the habitable-zone boundaries determined by the moist greenhouse (inner edge) and maximum greenhouse (outer edge) for host stars with 𝑇eff in the range 3000–7000 K according to Kopparapu et al. (2013). — astro-ph.EP

Chengzi Jiang, Aleksandra Selezneva, Hannu Parviainen, Felipe Murgas, Enric Pallé, Gareb Fernández-Rodríguez, Samuel Geraldía-González, Jaume Orell-Miquel, Norio Narita, Akihiko Fukui, Jerome de Leon, Izuru Fukuda, Kai Ikuta, Kiyoe Kawauchi, Steve B. Howell, Colin Littlefield, Sarah J. Deveny, Joseph D. Twicken, Richard P. Schwarz, Avi Shporer

Comments: 17 pages, 14 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2512.06817 [astro-ph.EP] (or arXiv:2512.06817v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2512.06817
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From: Chengzi Jiang
[v1] Sun, 7 Dec 2025 12:28:10 UTC (3,891 KB)
https://arxiv.org/abs/2512.06817
Astrobiology,