TOI-2285b: A 1.7 Earth-radius planet near the habitable zone around a nearby M dwarf

Akihiko Fukui, Tadahiro Kimura, Teruyuki Hirano, Norio Narita, Takanori Kodama, Yasunori Hori, Masahiro Ikoma, Enric Pallé, Felipe Murgas, Hannu Parviainen, Kiyoe Kawauchi, Mayuko Mori, Emma Esparza-Borges, Allyson Bieryla, Jonathan Irwin, Boris S. Safonov, Keivan G. Stassun, Leticia Alvarez-Hernandez, Víctor J.S. Béjar, Núria Casasayas-BarrisGuo Chen, Nicolas Crouzet, Jerome P. De Leon, Keisuke Isogai, Taiki Kagetani, Peter Klagyivik, Judith Korth, Seiya Kurita, Nobuhiko Kusakabe, John Livingston, Rafael Luque, Alberto Madrigal-Aguado, Giuseppe Morello, Taku Nishiumi, Jaume Orell-Miquel, Mahmoudreza Oshagh, Manuel Śanchez-Benavente, Monika Stangret, Yuka Terada, Noriharu Watanabe, Yujie Zou, Motohide Tamura, Takashi Kurokawa, Masayuki Kuzuhara, Jun Nishikawa, Masashi Omiya, Sébastien Vievard, Akitoshi Ueda, David W. Latham, Samuel N. Quinn, Ivan S. Strakhov, Alexandr A. Belinski, Jon M. Jenkins, George R. Ricker, Sara Seager, Roland Vanderspek, Joshua N. Winn, David Charbonneau, David R. Ciardi, Karen A. Collins, John P. Doty, Etienne Bachelet, Daniel Harbeck

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


We report the discovery of TOI-2285b, a sub-Neptune-sized planet transiting a nearby (42 pc) M dwarf with a period of 27.3 d. We identified the transit signal from the Transiting Exoplanet Survey Satellite photometric data, which we confirmed with ground-based photometric observations using the multiband imagers MuSCAT2 and MuSCAT3. Combining these data with other follow-up observations including high-resolution spectroscopy with the Tillinghast Reflector Echelle Spectrograph, high-resolution imaging with the SPeckle Polarimeter, and radial velocity (RV) measurements with the InfraRed Doppler instrument, we find that the planet has a radius of 1.74 ± 0.08, R⊕, a mass of < 19.5 M⊕ (95% c.l.), and an insolation flux of 1.54 ± 0.14 times that of the Earth. Although the planet resides just outside the habitable zone for a rocky planet, if the planet harbors an H2O layer under a hydrogen-rich atmosphere, then liquid water could exist on the surface of the H2O layer depending on the planetary mass and water mass fraction. The bright host star in the near-infrared (Ks = 9.0) makes this planet an excellent target for further RV and atmospheric observations to improve our understanding of the composition, formation, and habitability of sub-Neptune-sized planets.

Original languageEnglish (US)
Pages (from-to)L1-L8
JournalPublications of the Astronomical Society of Japan
Issue number1
StatePublished - Feb 1 2022

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • planets and satellites: detection
  • planets and satellites: individual (TOI-2285b)
  • planets and satellites: interiors
  • techniques: photometric
  • techniques: radial velocities


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