Exoplanets & Exomoons

TOI-4438 b: A Transiting Mini-Neptune Amenable To Atmospheric Characterization

By Keith Cowing
Status Report
March 19, 2024
Filed under , , , , , , , , ,
TOI-4438 b: A Transiting Mini-Neptune Amenable To Atmospheric Characterization
TPFs of TOI-4438 in TESS sectors 40, 52, and 53. The red bordered squares mark the optimal photometric aperture used to extract the SAP fluxes. The different sizes of the red circles show the G-band magnitudes from Gaia DR3 for all nearby stars with respect to TOI-4438 (marked with an “×”) up to ∆G = 10 mag fainter. — astro-ph.EP

We report the confirmation and mass determination of a mini-Neptune transiting the M3.5 V star TOI-4438 (G 182-34) every 7.44 days. A transit signal was detected with NASA’s TESS space mission in the sectors 40, 52, and 53.

In order to validate the planet TOI-4438 b and to determine the system properties, we combined TESS data with high-precision radial velocity measurements from the CARMENES spectrograph, spanning almost one year, and ground-based transit photometry. We found that TOI-4438 b has a radius of Rb = 2.52 +/- 0.13 R_Earth (5% precision), which together with a mass of Mb=5.4 +/- 1.1 M_Earth (20% precision), results in a bulk density of rho = 1.85+0.51-0.44 g cm-3 (28% precision), aligning the discovery with a volatile-rich planet.

Our interior structure retrieval with a pure water envelope yields a minimum water mass fraction of 46% (1-sigma). TOI-4438 b is a volatile-rich mini-Neptune with likely H/He mixed with molecules, such as water, CO2, and CH4. The primary star has a J-band magnitude of 9.7, and the planet has a high transmission spectroscopy metric (TSM) of 136 +/- 13. Taking into account the relatively warm equilibrium temperature of T_eq = 435 +/- 15 K, and the low activity level of its host star, TOI-4438 b is one of the most promising mini-Neptunes around an M dwarf for transmission spectroscopy studies.

E. Goffo, P. Chaturvedi, F. Murgas, G. Morello, J. Orell-Miquel, L. Acuña, L. Peña-Moñino, E. Pallé, A. P. Hatzes, S. Geraldía-González, F. J. Pozuelos, A. F. Lanza, D. Gandolfi, J. A. Caballero, M. Schlecker, M. Pérez-Torres, N. Lodieu, A. Schweitzer, C. Hellier, S. V. Jeffers, C. Duque-Arribas, C. Cifuentes, V. J. S. Béjar, M. Daspute, F. Dubois, S. Dufoer, E. Esparza-Borges, A. Fukui, Y. Hayashi, E. Herrero, M. Mori, N. Narita, H. Parviainen, L. Tal-Or, S. Vanaverbeke, I. Hermelo, P. J. Amado, S. Dreizler, Th. Henning, J. Lillo-Box, R. Luque, M. Mallorquín, E. Nagel, A. Quirrenbach, S. Reffert, A. Reiners, I. Ribas, P. Schöfer, H. M. Tabernero, M. Zechmeister

Comments: Accepted for publication on Astronomy & Astrophysics
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2403.09833 [astro-ph.EP] (or arXiv:2403.09833v1 [astro-ph.EP] for this version)
Submission history
From: Elisa Goffo
[v1] Thu, 14 Mar 2024 19:40:15 UTC (4,787 KB)


Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻