TOI-2285b: A 1.7 Earth-radius Planet Near the Habitable Zone around a Nearby M Dwarf

TL;DR

The paper reports the discovery and characterization of TOI-2285b, a sub-Neptune-sized planet near the habitable zone around a nearby M dwarf, using multiple observational methods to determine its properties and potential habitability.

Contribution

This study provides detailed measurements of a new exoplanet's size, mass constraints, and insolation, highlighting its suitability for future atmospheric and habitability studies.

Findings

Planet radius: 1.74 Earth radii

Mass upper limit: <19.5 Earth masses

Insolation flux: 1.54 times Earth's

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 days. 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 $<$ 19.5 $M_\oplus$ (95\% c.l.), and an insolation flux of 1.54 $\pm$ 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 H$_2$O layer under a hydrogen-rich atmosphere, then liquid water could exist on the surface of the H$_2$O layer depending on the planetary mass and water mass fraction. The bright host star in the near infrared ($K_s=9.0$) makes this planet an excellent target for further RV and atmospheric observations to improve our understanding on the composition, formation, and habitability of sub-Neptune-sized planets.