Two temperate Earth- and Neptune-sized planets orbiting fully convective M dwarfs
Year: 2026
Type: article
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.
Authors: Madison G Scott, Georgina Dransfield, Mathilde Timmermans, Amaury H M J Triaud, Benjamin V Rackham, Khalid Barkaoui, Adam J Burgasser, Karen A Collins, Michaël Gillon, Steve B Howell, Alan M Levine, Francisco J Pozuelos, Keivan G Stassun, Carl Ziegler, Yilen Gomez Maqueo Chew, Catherine A Clark, Yasmin Davis, Fatemeh Davoudi, Tansu Daylan, Brice-Olivier Demory, Dax Feliz, Akihiko Fukui, Maximilian N Günther, Emmanuël Jehin, Florian Lienhard, Andrew W Mann, Clàudia Janó Muñoz, Norio Narita, Peter P Pedersen, Richard P Schwarz, Avi Shporer, Abderahmane Soubkiou, Sebastián Zúñiga-Fernández
Institutions: University of Birmingham, University of Oxford, University of Liège, Massachusetts Institute of Technology, Instituto de Astrofísica de Canarias, University of California San Diego, Center for Astrophysics Harvard & Smithsonian, Ames Research Center, Instituto de Astrofísica de Andalucía, Vanderbilt University, Stephen F. Austin State University, Universidad Nacional Autónoma de México, California Institute of Technology, NASA Exoplanet Science Institute, Washington University in St. Louis, University of Bern, Center for Space and Habitability, Flatiron Institute, The University of Tokyo, European Space Agency, European Space Research and Technology Centre, ETH Zurich, Institute for Particle Physics and Astrophysics, University of North Carolina at Chapel Hill, University of Cambridge, Astrobiology Center
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,046
Funders: National Science Foundation, National Aeronautics and Space Administration, Simons Foundation, UK Research and Innovation, University of Birmingham, Japan Science and Technology Corporation, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Fonds De La Recherche Scientifique - FNRS, Fondation Merac, Science and Technology Facilities Council, European Research Council, Japan Society for the Promotion of Science
Awards: G1232319559, G1437537017, G15571430, TTV法によるM型星まわりの小型惑星の組成分布とその起源の解明, G1853635042, G18599350, Red-enhanced cameras to seek rocky planets transiting Ultra-Cool Dwarfs, G2209429583, Exoplanets orbiting brown dwarfs, G3228472174, G3319482958, G4334099265, G4502305455, G4623258783, G4643853793, G4986430458, G580951548, Discovering and probing the atmospheres of rocky exoplanets, G6686480456, Discovering and probing the atmospheres of rocky exoplanets, G7288031051, G753082317, G7553243680, G7948010765, A Study for Unveiling Planetary Evolution with Young Transiting Exoplanets, G8419093221, G8549473033, G8597195001, G8625566128, G878044590
OpenAlex ID: W7123359680