TOI-2285b: A 1.7 Earth-radius planet near the habitable zone around a nearby M dwarf
Bieryla, Allyson; Latham, David W.; Quinn, Samuel N.; Tamura, Motohide; Stassun, Keivan G.; Hirano, Teruyuki; Collins, Karen A.; Ricker, George R.; Vanderspek, Roland; Seager, Sara; Winn, Joshua N.; Jenkins, Jon M.; Crouzet, Nicolas; Ciardi, David R.; de Leon, Jerome P.; Fukui, Akihiko; Korth, Judith; Kuzuhara, Masayuki; Narita, Norio; Luque, Rafael; Terada, Yuka; Omiya, Masashi; Charbonneau, David; Morello, Giuseppe; Kusakabe, Nobuhiko; Livingston, John; Murgas, Felipe; Irwin, Jonathan; Chen, Guo; Doty, John P.; Kawauchi, Kiyoe; Orell-Miquel, Jaume; Pallé, Enric; Harbeck, Daniel; Hori, Yasunori; Nishikawa, Jun; Kurokawa, Takashi; Ueda, Akitoshi; Parviainen, Hannu; Esparza-Borges, Emma; Kodama, Takanori; Isogai, Keisuke; Ikoma, Masahiro; Mori, Mayuko; Oshagh, Mahmoudreza; Watanabe, Noriharu; Bachelet, Etienne; Nishiumi, Taku; Kagetani, Taiki; Kimura, Tadahiro; Zou, Yujie; Casasayas-Barris, Núria; Safonov, Boris S.; Belinski, Alexandr A.; Kurita, Seiya; Vievard, Sébastien; Alvarez-Hernandez, Leticia; Béjar, Víctor J. S.; Klagyivik, Peter; Madrigal-Aguado, Alberto; Sánchez-Benavente, Manuel; Stangret, Monika; Strakhov, Ivan S.
Japan, Spain, United States, Russia, Netherlands, China, Germany, Sweden, Taiwan
Abstract
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 $1.74 \pm 0.08\, R_\oplus$, a mass of $\lt \!\!19.5\,M_\oplus$ ($95\%$ 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.