A super-Earth and a mini-Neptune near the 2:1 MMR straddling the radius valley around the nearby mid-M dwarf TOI-2096

¹ Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
e-mail: fjpozuelos@uliege.be
² Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
³ Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
⁴ Cavendish Laboratory, JJ Thomson Avenue, Cambridge, CB3 0HE, UK
⁵ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁶ AIM, CEA, CNRS, Université Paris-Saclay, Université de Paris, 91191 Gif-sur-Yvette, France
⁷ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁸ Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
⁹ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
¹⁰ Department of Astronomy & Astrophysics, University of Chicago, Chicago, IL 60637, USA
¹¹ Center for Astrophysics and Space Sciences, UC San Diego, UCSD Mail Code 0424, 9500 Gilman Drive, La Jolla, CA 92093-0424, USA
¹² Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, 1800 Sherman, Evanston, IL, 60201, USA
¹³ Department of Astrophysical & Planetary Sciences, University of Colorado Boulder, 2000 Colorado Avenue, Boulder, CO 80309, USA
¹⁴ Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521, USA
¹⁵ Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
¹⁶ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁷ Department of Physics & Astronomy, Vanderbilt University, 6301 Stevenson Center Ln., Nashville, TN 37235, USA
¹⁸ Université de Montréal, Département de Physique, IREX, Montréal, QC H3C 3J7, Canada
¹⁹ Observatoire du Mont-Mégantic, Université de Montréal, Montréal H3C 3J7, Canada
²⁰ NASA Exoplanet Science Institute, Caltech/IPAC, Mail Code 10022, 1200 E. California Blvd., Pasadena, CA 91125, USA
²¹ NASA Ames Research Center, Moffett Field, CA 94035, USA
²² NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
²³ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
²⁴ School of Physics & Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
²⁵ Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA, 02138, USA
²⁶ Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
²⁷ Universidad Nacional Autönoma de México, Instituto de Astronomía, AP 70-264, Ciudad de México, 04510, México
²⁸ European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
²⁹ Dpt. Física Teòrica y del Cosmos, Universidad de Granada, Campus de Fuentenueva s/n, 18071 Granada, Spain
³⁰ Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, Faculty of sciences Semlalia, Cadi Ayyad University, Marrakech, Morocco
³¹ The CHARA Array, Georgia State University, USA
³² Steward Observatory and Department of Astronomy, The University of Arizona, Tucson, AZ 85721, USA
³³ Lunar and Planetary Laboratory and Department of Planetary Sciences, The University of Arizona, Tucson, AZ 85721, USA
³⁴ Vatican Observatory, 00120 Città del Vaticano  
³⁵ Graduate Institute of Astronomy, National Central University, Taoyuan 32001, Taiwan
³⁶ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
³⁷ Department of Physics, University of Rome “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Rome, Italy
³⁸ INAF – Turin Astrophysical Observatory, via Osservatorio 20, 10025 Pino Torinese, Italy
³⁹ International Institute for Advanced Scientific Studies (IIASS), Via G. Pellegrino 19, I-84019, Vietri sul Mare (SA), Italy

Received: 11 November 2022
Accepted: 6 February 2023

Abstract

Context. Several planetary formation models have been proposed to explain the observed abundance and variety of compositions of super-Earths and mini-Neptunes. In this context, multitransiting systems orbiting low-mass stars whose planets are close to the radius valley are benchmark systems, which help to elucidate which formation model dominates.

Aims. We report the discovery, validation, and initial characterization of one such system, TOI-2096 (TIC 142748283), a two-planet system composed of a super-Earth and a mini-Neptune hosted by a mid-type M dwarf located 48 pc away.

Methods. We characterized the host star by combining optical spectra, analyzing its broadband spectral energy distribution, and using evolutionary models for low-mass stars. Then, we derived the planetary properties by modeling the photometric data from TESS and ground-based facilities. In addition, we used archival data, high-resolution imaging, and statistical validation to support our planetary interpretation.

Results. We found that the stellar properties of TOI-2096 correspond to a dwarf star of spectral type M4±0.5. It harbors a super-Earth (R = 1.24 ± 0.07 R_⊕) and a mini-Neptune (R = 1.90 ± 0.09 R_⊕) in likely slightly eccentric orbits with orbital periods of 3.12 d and 6.39 d, respectively. These orbital periods are close to the first-order 2:1 mean-motion resonance (MMR), a configuration that may lead to measurable transit timing variations (TTVs). We computed the expected TTVs amplitude for each planet and found that they might be measurable with high-precision photometry delivering mid-transit times with accuracies of ≲2 min. Moreover, we conclude that measuring the planetary masses via radial velocities (RVs) could also be possible. Lastly, we found that these planets are among the best in their class to conduct atmospheric studies using the NIRSpec/Prism onboard the James Webb Space Telescope (JWST).

Conclusions. The properties of this system make it a suitable candidate for further studies, particularly for mass determination using RVs and/or TTVs, decreasing the scarcity of systems that can be used to test planetary formation models around low-mass stars.