TOI-2322: Two transiting rocky planets close to the stellar rotation period and its first harmonic

¹ Observatoire de Genève, Département d’Astronomie, Université de Genève, Chemin Pegasi 51b, 1290 Versoix, Switzerland
² Instituto de Astrofísica de Canarias, c/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁴ Department of Physics, University of Oxford, Oxford OX1 3RH, UK
⁵ Instituto de Astrofísica e Ciências do Espaço, CAUP, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
⁶ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
⁷ Institut d’Estudis Espacials de Catalunya (IEEC), Edifici RDIT, Campus UPC, 08860 Castelldefels (Barcelona), Spain
⁸ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, c/ de Can Magrans s/n, 08193 Cerdanyola del Vallès, Barcelona, Spain
⁹ Physics Institute, University of Bern, Gesellsschaftstrasse 6, 3012 Bern, Switzerland
¹⁰ Center for Space and Habitability, University of Bern, Gesellsschaftstrasse 6, 3012 Bern, Switzerland
¹¹ Centro de Astrobiología, CSIC-INTA, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
¹² Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹³ INAF – Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34143 Trieste, Italy
¹⁴ IFPU–Institute for Fundamental Physics of the Universe, via Beirut 2, 34151 Trieste, Italy
¹⁵ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
¹⁶ Department of Physics and Astronomy, University of New Mexico, 210 Yale Boulevard, Albuquerque, NM 87131, USA
¹⁷ European Southern Observatory, Av. Alonso de Cordova, 3107 Vitacura, Santiago de Chile, Chile
¹⁸ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 70 Vassar St, Cambridge, MA 02139, USA
¹⁹ Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
²⁰ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
²¹ Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências da Universidade de Lisboa, 1749-016 Lisboa, Portugal
²² Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
²³ Subaru Telescope, National Astronomical Observatory of Japan (NAOJ), 650 N Aohoku Place, Hilo, HI 96720, USA
²⁴ SETI Institute, Mountain View, CA 94043, USA/NASA Ames Research Center, Moffett Field, CA 94035, USA
²⁵ Department of Physics, Engineering and Astronomy, Stephen F. Austin State University, 1936 North St, Nacogdoches, TX 75962, USA

^★ Corresponding author: melissa.hobson@unige.ch

Received: 21 May 2025
Accepted: 25 August 2025

Abstract

Context. Active regions on the stellar surface can induce quasi-periodic radial velocity (RV) variations that can mimic planets and mask true planetary signals. These spurious signals can be problematic for RV surveys such as those carried out by the ESPRESSO consortium.

Aims. Using ESPRESSO and HARPS RVs and activity indicators, we aim to confirm and characterise two candidate transiting planets from TESS orbiting a K4 star with strong activity signals.

Methods. From the ESPRESSO FWHM, TESS photometry, and ASAS-SN photometry, we measure a stellar rotation period of 21.28 ± 0.08 d. We jointly model the TESS photometry, ESPRESSO and HARPS RVs, and activity indicators, applying a multivariate Gaussian process (GP) framework to the spectroscopic data.

Results. We are able to disentangle the planetary and activity components, finding that TOI-2322 b has a 11.307170_−0.000079^+0.000085 d period, close to the first harmonic of the rotation period, a ≤2.03 M_⊕ mass upper limit and a 0.994_−0.059^+0.057 R_⊕ radius. TOI-2322 c orbits close to the stellar rotation period, with a 20.225528_−0.000044^+0.000039 d period; it has a 18.10_−5.36^+4.34 M_⊕ mass and a 1.874_−0.057^+0.066 R_⊕ radius.

Conclusions. The multivariate GP framework is crucial to separating the stellar and planetary signals, significantly outperforming a one-dimensional GP. Likewise, the transit data is fundamental to constraining the periods and epochs, enabling the retrieval of the planetary signals in the RVs. The internal structure of TOI-2322 c is very similar to that of Earth, making it one of the most massive planets with an Earth-like composition known.