TOI-3568 b: A super-Neptune in the sub-Jovian desert

¹ Laboratório Nacional de Astrofísica, Rua Estados Unidos 154, 37504-364 Itajubá, MG, Brazil,
² Institut d’Astrophysique de Paris, CNRS, UMR 7095, Sorbonne Université, 98 bis bd Arago, 75014 Paris, France
³ Universidad Nacional de Córdoba – Observatorio Astronómico de Córdoba, Laprida 854, X5000BGR, Córdoba, Argentina
⁴ Consejo Nacional de Investigaciones Científicas y Técnicas (CON-ICET), Godoy Cruz 2290, CABA, CPC 1425FQB, Argentina
⁵ Observatoire de Haute Provence, St Michel l’Observatoire, France
⁶ Universidade Federal do Rio de Janeiro, Observatório do Valongo, Ladeira do Pedro Antônio, 43, Rio de Janeiro, RJ 20080-090, Brazil
⁷ Instituto de Astronomía, Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de México, 04510, Mexico
⁸ International Center for Advanced Studies (ICAS) and ICIFI (CON-ICET), ECyT-UNSAM, Campus Miguelete, 25 de Mayo y Francia, 1650 Buenos Aires, Argentina
⁹ NASA Ames Research Center, Moffett Field, CA 94035, USA
¹⁰ Research Institute for Advanced Computer Science, Universities Space Research Association, Washington, DC 20024, USA
¹¹ Canada-France-Hawaii Telescope, CNRS, Kamuela, HI 96743, USA
¹² Université de Montréal, Département de Physique, IREX, Montréal, QC H3C 3J7, Canada
¹³ Department of Astronomy & Astrophysics, University of Chicago, Chicago, IL, USA
¹⁴ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹⁵ Aix-Marseille Univ., CNRS, CNES, LAM, 38 rue Frédéric Joliot-Curie, 13388 Marseille, France
¹⁶ Université Grenoble Alpes, CNRS, IPAG, 414 rue de la Piscine, 38400 St-Martin-d’Hères, France
¹⁷ Université de Toulouse, CNRS, IRAP, 14 avenue Belin, 31400 Toulouse, France
¹⁸ NASA Exoplanet Science Institute, Caltech IPAC, 1200 E. California Blvd., Pasadena, CA 91125, USA
¹⁹ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
²⁰ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²¹ Department of Astronomy, Wellesley College, Wellesley, MA 02481, USA
²² Universidade de São Paulo, Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG), Departamento de Astronomia, Rua do Matão 1226, Cidade Universitária, 05508-900, SP, Brazil
²³ NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
²⁴ Royal Astronomical Society, Burlington House, Piccadilly, London W1J 0BQ, UK
²⁵ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
²⁶ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
²⁷ SETI Institute, Mountain View, CA 94043, USA

^★ Corresponding author; martioli@iap.fr

Received: 12 April 2024
Accepted: 4 September 2024

Abstract

The sub-Jovian desert is a region in the mass-period and radius-period parameter space that typically encompasses short-period ranges between super-Earths and hot Jupiters, and exhibits an intrinsic dearth of planets. This scarcity is likely shaped by photoevaporation caused by the stellar irradiation received by giant planets that have migrated inward. We report the detection and characterization of TOI-3568 b, a transiting super-Neptune with a mass of 26.4 ± 1.0 M_⊕, a radius of 5.30 ± 0.27 R_⊕, a bulk density of 0.98 ± 0.15 g cm⁻³, and an orbital period of 4.417965 (5) d situated in the vicinity of the sub-Jovian desert. This planet orbiting a K dwarf star with solar metallicity was identified photometrically by the Transiting Exoplanet Survey Satellite (TESS). It was characterized as a planet by our high-precision radial-velocity (RV) monitoring program using MAROON-X at Gemini North, supplemented with additional observations from the SPICE large program with SPIRou at CFHT. We performed a Bayesian MCMC joint analysis of the TESS and ground-based photometry, and MAROON-X and SPIRou RVs, to measure the orbit, radius, and mass of the planet, as well as a detailed analysis of the high-resolution flux and polarimetric spectra to determine the physical parameters and elemental abundances of the host star. Our results reveal TOI-3568 b to be a hot super-Neptune rich in hydrogen and helium, with a core of heavier elements of between 10 and 25 M_⊕ in mass. We analyzed the photoevaporation status of TOI-3568 b and find that it experiences one of the highest extreme-ultraviolet (EUV) luminosities among planets with a mass of M_p < 2 M_Nep, yet it has an evaporation lifetime exceeding 5 Gyr. Positioned in the transition between two significant populations of exoplanets on the mass-period and energy diagrams, this planet presents an opportunity to test theories concerning the origin of the sub-Jovian desert.