NGTS-30b/TOI-4862b: An ~1 Gyr old 98-day transiting warm Jupiter^★,★★

¹ Observatoire Astronomique de l’Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
e-mail: matthew.battley@unige.ch
² Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
³ Physikalisches Institut, University of Bern, Gesellsschaftstrasse 6, 3012 Bern, Switzerland
⁴ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁵ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁶ Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Av. Diagonal las Torres 2640, Peñalolén Santiago, Chile
⁷ Millennium Institute for Astrophysics, Chile
⁸ Data Observatory Foundation, Santiago, Chile
⁹ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA
¹⁰ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
¹¹ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
¹² Department of Physics, Engineering and Astronomy, Stephen F. Austin State University, 1936 North St, Nacogdoches, TX 75962, USA
¹³ Instituto de Astronomía, Universidad Católica del Norte, Angamos 0610, 1270709, Antofagasta, Chile
¹⁴ Las Campanas Observatory, Carnegie Institution for Science, Colina el Pino, Casilla 601 La Serena, Chile
¹⁵ School of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
¹⁶ Earth and Planets Laboratory, Carnegie Institution for Science, 5241 Broad Branch Road, NW, Washington, DC 20015, USA
¹⁷ Caltech/IPAC-NASA Exoplanet Science Institute, 770 S. Wilson Avenue, Pasadena, CA 91106, USA
¹⁸ The Observatories of the Carnegie Institution for Science, 813 Santa Barbara St., Pasadena, CA 91101, USA
¹⁹ Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
²⁰ Department of Physics and McDonnell Center for the Space Sciences, Washington University, St. Louis, MO 63130, USA
²¹ Astronomy Unit, Queen Mary University of London, Mile End Road, London E1 4NS, UK
²² European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
²³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²⁴ Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
²⁵ Centro de Astrofísica y Tecnologías Afines (CATA), Casilla 36-D, Santiago, Chile
²⁶ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139, USA
²⁷ NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
²⁸ Department of Astronomy, Yale University, New Haven, CT 06511, USA
²⁹ Center for Data Intensive and Time Domain Astronomy, Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA
³⁰ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
³¹ Department of Aeronautics and Astronautics, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
³² Insitute of Planetary Research, German Aerospace Center (DLR), Rutherfordstr. 2, 12489 Berlin, Germany
³³ Earth and Planets Laboratory, Carnegie Institution for Science, 5241 Broad Branch Rd NW, Washington, DC 20015, USA
³⁴ NASA Ames Research Center, Moffett Field, CA 94035, USA
³⁵ Astrophysics Research Centre, Queen’s University Belfast, Belfast BT7 1NN, UK
³⁶ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA

Received: 22 January 2024
Accepted: 27 March 2024

Abstract

Context. Long-period transiting exoplanets bridge the gap between the bulk of transit- and Doppler-based exoplanet discoveries, providing key insights into the formation and evolution of planetary systems. The wider separation between these planets and their host stars results in the exoplanets typically experiencing less radiation from their host stars; hence, they should maintain more of their original atmospheres, which can be probed during transit via transmission spectroscopy. Although the known population of long-period transiting exoplanets is relatively sparse, surveys performed by the Transiting Exoplanet Survey Satellite (TESS) and the Next Generation Transit Survey (NGTS) are now discovering new exoplanets to fill in this crucial region of the exoplanetary parameter space.

Aims. This study aims to characterise a new long-period transiting exoplanet by following up on a single-transit candidate found in the TESS mission.

Methods. The TOI-4862 system was monitored using a combination of photometric instruments (TESS, NGTS, and EulerCam) and spectroscopic instruments (CORALIE, FEROS, HARPS, and PFS) in order to determine the period, radius, and mass of the long-period transiting exoplanet NGTS-30 b/TOI-4862 b. These observations were then fitted simultaneously to determine precise values for the properties and orbital parameters of the exoplanet, as well as the refined stellar parameters of the host star.

Results. We present the discovery of a long-period (P = 98.29838 ± 0.00010 day) Jupiter-sized (0.928 ± 0.032 R_J; 0.960 ± 0.056 M_J) planet transiting a 1.1 Gyr old G-type star, one of the youngest warm Jupiters discovered to date. NGTS-30 b/TOI-4862 b has a moderate eccentricity (0.294_−0.010^+0.014), meaning that its equilibrium temperature can be expected to vary from 274₋₄₆⁺³⁰ K to 500₋₈₄⁺⁵⁵ K over the course of its orbit. Through interior modelling, NGTS-30 b/TOI-4862b was found to have a heavy element mass fraction of 0.23_−0.06^+0.05 and a heavy element enrichment (Z_p/Z_★) of 20₋₆⁺⁵, making it metal-enriched compared to its host star.

Conclusions. NGTS-30 b/TOI-4862 b is one of the youngest well-characterised long-period exoplanets found to date and will therefore be important in the quest to understanding the formation and evolution of exoplanets across the full range of orbital separations and ages.