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arXiv · 2512.06817

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

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
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Abstract

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 $R_{\oplus}$) orbits its M3V star with a period of $\sim$18.79 days, well within the habitable zone ($\sim$0.98 Earth insolation). TOI-7166 b (2.39 $R_{\oplus}$) orbits its M4.5V host star with a period of $\sim$12.92 days, placing it near the inner edge of the habitable zone ($\sim$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.

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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. 2026-03-17. Multicolour Validation of Two Temperate Mini-Neptunes Around M-dwarf Habitable Zones. https://doi.org/10.1093/mnras%2Fstag367

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