Two temperate Earth-mass planets orbiting the nearby star GJ 1002^{★,★★,★★★}

¹ Instituto de Astrofísica de Canarias, c/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
e-mail: asm@iac.es
² Departamento de Astrofísica, Universidad de La Laguna, Avda. Astrofísico Francisco Sánchez s/n, 38206 La Laguna, Tenerife, Spain
³ Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
⁴ Centro de Astrobiología (CSIC-INTA), ESAC, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁵ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CauP, Rua das Estrelas, 4150-762 Porto, Portugal
⁶ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua Campo Alegre, 4169-007 Porto, Portugal
⁷ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
⁸ Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019, USA
⁹ Département d’astronomie de l’Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
¹⁰ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
¹¹ Consejo Superior de Investigaciones Científicas, c/ de Serrano 117, 28006 Madrid, Spain
¹² INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34143 Trieste, Italy
¹³ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, c/ Can Magrans s/n, 08193 Bellaterra, Barcelona, Spain
¹⁴ Institut d’Estudis Espacials de Catalunya (IEEC), c/ Gran Capità 2-4, 08034 Barcelona, Spain
¹⁵ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹⁶ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
¹⁷ Institut für Astrophysik und Geophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
¹⁸ Physikalisches Institut, Universität Bern, Siedlerstrasse 5, 3012 Bern, Switzerland
¹⁹ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
²⁰ Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126, Pisa, Italy
²¹ Centre Vie dans l’Univers, Faculté des sciences de l’Université de Genève, Quai Ernest-Ansermet 30, 1205 Geneva, Switzerland
²² Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
²³ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
²⁴ Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
²⁵ Departamento de Física de la Tierra y Astrofísica and IPARCOSUCM (Instituto de Física de Partículas y del Cosmos de la UCM), Ciudad Universitaria, 28040 Madrid, Spain
²⁶ Centro Astronómico Hispano en Andalucía, Observatorio de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Almería, Spain
²⁷ Department of Physics, Ariel University, Ariel 40700, Israel

Received: 16 September 2022
Accepted: 21 November 2022

Abstract

We report the discovery and characterisation of two Earth-mass planets orbiting in the habitable zone of the nearby M-dwarf GJ 1002 based on the analysis of the radial-velocity (RV) time series from the ESPRESSO and CARMENES spectrographs. The host star is the quiet M5.5 V star GJ 1002 (relatively faint in the optical, V ~ 13.8 mag, but brighter in the infrared, J ~ 8.3 mag), located at 4.84 pc from the Sun. We analyse 139 spectroscopic observations taken between 2017 and 2021. We performed a joint analysis of the time series of the RV and full-width half maximum (FWHM) of the cross-correlation function (CCF) to model the planetary and stellar signals present in the data, applying Gaussian process regression to deal with the stellar activity. We detect the signal of two planets orbiting GJ 1002. GJ 1002 b is a planet with a minimum mass m_p sin i of 1.08 ± 0.13 M_⊕ with an orbital period of 10.3465 ± 0.0027 days at a distance of 0.0457 ± 0.0013 au from its parent star, receiving an estimated stellar flux of 0.67 F_⊕. GJ 1002 c is a planet with a minimum mass m_p sin i of 1.36 ± 0.17 M_⊕ with an orbital period of 20.202 ± 0.013 days at a distance of 0.0738 ± 0.0021 au from its parent star, receiving an estimated stellar flux of 0.257 F_⊕. We also detect the rotation signature of the star, with a period of 126 ± 15 days. We find that there is a correlation between the temperature of certain optical elements in the spectrographs and changes in the instrumental profile that can affect the scientific data, showing a seasonal behaviour that creates spurious signals at periods longer than ~200 days. GJ 1002 is one of the few known nearby systems with planets that could potentially host habitable environments. The closeness of the host star to the Sun makes the angular sizes of the orbits of both planets (~9.7 mas and ~15.7 mas, respectively) large enough for their atmosphere to be studied via high-contrast high-resolution spectroscopy with instruments such as the future spectrograph ANDES for the ELT or the LIFE mission.