Two temperate Earth- and Neptune-sized planets orbiting fully convective M dwarfs

ABSTRACT As the diversity of exoplanets continues to grow, it is important to revisit assumptions about habitability and classical habitable zone definitions. In this work, we introduce an expanded ‘temperate’ zone, defined by instellation fluxes in the range $0.1< S/\mathrm{S}_{\oplus }< 5$, thus encompassing a broader range of potentially habitable worlds. We also introduce the TEMPOS survey, which aims to produce a catalogue of precise radii for temperate planets orbiting M dwarfs with $T_\mathrm{eff}\le 3400\,$ K. This work reports the discovery and characterization of two planets in this temperate regime orbiting mid-type M dwarfs: TOI-6716 b, a $R_\mathrm{b}=0.98\pm 0.07\, \mathrm{R}_{\oplus }$ planet orbiting its M4 host star ($R_\star =0.231\, \pm 0.015\mathrm{R}\, _\odot$, $M_\star =0.223\pm 0.011\, \mathrm{M}\, _\odot$, $T_\mathrm{eff}=3110\pm 80\, \mathrm{K}$) with a period $P=4.7185898^{+0.0000054}_{-0.0000041}\, \mathrm{d}$, and TOI-7384 b, a $R_\mathrm{b}=3.56\pm 0.21\, \mathrm{R}_{\oplus }$ planet orbiting an M4 ($R_\star =0.319\, \pm 0.018\mathrm{R}\, _\odot$, $M_\star =0.318\pm 0.016\, \mathrm{M}\, _\odot$, $T_\mathrm{eff}=3185\pm 75\, \mathrm{K}$) star every $P=6.2340258^{+0.0000034}_{-0.0000036}\, \mathrm{d}$. The radii of TOI-6716 b and TOI-7384 b have precisions of 6.8 per cent and 5.9 per cent, respectively. We validate these planets with multiband ground-based photometric observations, high-resolution imaging, and statistical analyses. We find these planets to have instellation fluxes close to the inner (hotter) edge of the temperate zone, with $S_\mathrm{b}=4.4\pm 1.1\, \mathrm{S}_{\oplus }$ and $S_\mathrm{b}=4.9\pm 1.1\, \mathrm{S}_{\oplus }$ for TOI-6716 b and TOI-7384 b, respectively. Also, with a predicted transmission spectroscopy metric similar to the TRAPPIST-1 planets, TOI-6716 b is likely to be a good rocky-world James Webb Space Telescope target, should it have retained its atmosphere.

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Journal
Monthly Notices of the Royal Astronomical Society
Published
2026-01-13
DOI
https://doi.org/10.1093/mnras/stag070
Primary Topic
Stellar, planetary, and galactic studies
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article
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article

Two temperate Earth- and Neptune-sized planets orbiting fully convective M dwarfs

B. V. Rackham, Maximilian N. Günther, A. Shporer, F. J. Pozuelos et al.
Monthly Notices of the Royal Astronomical Society
Stellar, planetary, and galactic studies
article

Two temperate Earth- and Neptune-sized planets orbiting fully convective M dwarfs

B. V. Rackham, Maximilian N. Günther, A. Shporer, F. J. Pozuelos, Georgina Dransfield, Adam J. Burgasser, Sebastián Zúñiga-Fernández, Abderahmane Soubkiou, P. P. Pedersen, Yasmin Davis, Florian Lienhard, Richard P. Schwarz, Mathilde Timmermans, Khalid Barkaoui, Catherine A. Clark, M. Gillon, A. Fukui, M. G. Scott, Carl Ziegler, Norio Narita, Brice-Olivier Demory, Keivan G Stassun, Emmanuël Jehin, Andrew W Mann, Dax Feliz, Karen A Collins, Fatemeh Davoudi, Clàudia Janó Muñoz, Tansu Daylan, Alan M Levine, Amaury H M J Triaud, Steve B Howell
article en

Abstract

ABSTRACT As the diversity of exoplanets continues to grow, it is important to revisit assumptions about habitability and classical habitable zone definitions. In this work, we introduce an expanded ‘temperate’ zone, defined by instellation fluxes in the range $0.1< S/\mathrm{S}_{\oplus }< 5$, thus encompassing a broader range of potentially habitable worlds. We also introduce the TEMPOS survey, which aims to produce a catalogue of precise radii for temperate planets orbiting M dwarfs with $T_\mathrm{eff}\le 3400\,$ K. This work reports the discovery and characterization of two planets in this temperate regime orbiting mid-type M dwarfs: TOI-6716 b, a $R_\mathrm{b}=0.98\pm 0.07\, \mathrm{R}_{\oplus }$ planet orbiting its M4 host star ($R_\star =0.231\, \pm 0.015\mathrm{R}\, _\odot$, $M_\star =0.223\pm 0.011\, \mathrm{M}\, _\odot$, $T_\mathrm{eff}=3110\pm 80\, \mathrm{K}$) with a period $P=4.7185898^{+0.0000054}_{-0.0000041}\, \mathrm{d}$, and TOI-7384 b, a $R_\mathrm{b}=3.56\pm 0.21\, \mathrm{R}_{\oplus }$ planet orbiting an M4 ($R_\star =0.319\, \pm 0.018\mathrm{R}\, _\odot$, $M_\star =0.318\pm 0.016\, \mathrm{M}\, _\odot$, $T_\mathrm{eff}=3185\pm 75\, \mathrm{K}$) star every $P=6.2340258^{+0.0000034}_{-0.0000036}\, \mathrm{d}$. The radii of TOI-6716 b and TOI-7384 b have precisions of 6.8 per cent and 5.9 per cent, respectively. We validate these planets with multiband ground-based photometric observations, high-resolution imaging, and statistical analyses. We find these planets to have instellation fluxes close to the inner (hotter) edge of the temperate zone, with $S_\mathrm{b}=4.4\pm 1.1\, \mathrm{S}_{\oplus }$ and $S_\mathrm{b}=4.9\pm 1.1\, \mathrm{S}_{\oplus }$ for TOI-6716 b and TOI-7384 b, respectively. Also, with a predicted transmission spectroscopy metric similar to the TRAPPIST-1 planets, TOI-6716 b is likely to be a good rocky-world James Webb Space Telescope target, should it have retained its atmosphere.

Monthly Notices of the Royal Astronomical SocietyVol. 547(1)
University of North Carolina at Chapel Hill (US), James S. McDonnell Foundation (US), University of Bern (CH), California Institute of Technology (US), Ames Research Center (US), Planetary Science Institute (US), University of Liège (BE), Universidad Autónoma de la Ciudad de México (MX), Vanderbilt University (US), Stephen F. Austin State University (US), Northeast Catholic College (US), NASA Exoplanet Science Institute (US), ETH Zurich (CH), University of California San Diego (US), University of Oxford (GB), Astrobiology Center (JP), Center for Astrophysics Harvard & Smithsonian (US), Instituto de Astrofísica de Canarias (ES), Tokyo Metropolitan Komaba High School (JP), Flatiron Health (United States) (US), Instituto de Astrofísica de Andalucía (ES), European Space Research and Technology Centre (NL), Massachusetts Institute of Technology (US), The University of Tokyo (JP), University of Birmingham (GB), Universidad Nacional Autónoma de México (MX)
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Stellar, planetary, and galactic studies
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