Astronomy and Astrophysics
Aims: We aim to validate and characterize the new sub-Neptune-sized planet candidate TOI-2136.01 orbiting a nearby M dwarf (d = 33.36 ± 0.02pc, Teff = 3373 ± 108 K) with an orbital period of 7.852 days.
Methods: We use TESS data, ground-based multicolor photometry, and radial velocity measurements with the InfraRed Doppler (IRD) instrument on the Subaru Telescope to validate the planetary nature of TOI-2136.01, and estimate the stellar and planetary parameters. We also conduct high-resolution transmission spectroscopy to search for helium in its atmosphere.
Results: We confirm that TOI-2136.01 (now named TOI-2136b) is a bona fide planet with a planetary radius of Rp = 2.20 ± 0.07R⊕ and a mass of Mp = 4.7−2.6+3.1 M⊕. We also search for helium 10830 Å absorption lines and place an upper limit on the equivalent width of <7.8 mÅ and on the absorption signal of <1.44% with 95% confidence.
Conclusions: TOI-2136b is a sub-Neptune transiting a nearby and bright star (J = 10.8 mag), and is a potentially hycean planet, which is a new class of habitable planets with large oceans under a H2-rich atmosphere, making it an excellent target for atmospheric studies to understand the formation, evolution, and habitability of the small planets.
The search for life in the universe has been driven by recent discoveries of planets around other stars (known as exoplanets), becoming one of the most active fields in modern astrophysics. The growing number of new exoplanets discovered in recent years and the recent advance on the study of their atmospheres are not only providing new valuable