The CARMENES search for exoplanets around M dwarfs

Wolf 1069 b: Earth-mass planet in the habitable zone of a nearby, very low-mass star^★

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: astrodianakossakowski@gmail.com
² Department of Astronomy, Sofia University “St Kliment Ohridski”, 5 James Bourchier Blvd, 1164 Sofia, Bulgaria
³ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
⁴ Centro de Astrobiología (CSIC-INTA), ESAC, Camino bajo del castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁵ NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
⁶ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
⁷ Center for Research and Exploration in Space Science and Technology, NASA/GSFC, Greenbelt, MD 20771, USA
⁸ American University, College of Arts and Sciences, Washington DC, USA
⁹ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
¹⁰ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹¹ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, C/ de Can Magrans s/n, 08193 Cerdanyola del Vallès, Spain
¹² Institut d’Estudis Espacials de Catalunya (IEEC), C/ Gran Capità 2-4, 08034 Barcelona, Spain
¹³ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹⁴ Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
¹⁵ Institut für Astrophysik und Geophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
¹⁶ Centro Astronónomico Hispano en Andalucía, Observatorio de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Spain
¹⁷ Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
¹⁸ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
¹⁹ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig Weg 3, 37077 Göttingen, Germany
²⁰ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
²¹ Departamento de Física de la Tierra y Astrofísica & IPARCOSUCM (Instituto de Física de Partículas y del Cosmos de la UCM), Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
²² Department of Physics, Ariel University, Ariel 40700, Israel
²³ School of Sciences, European University Cyprus, Diogenes street, Engomi, 1516 Nicosia, Cyprus
²⁴ Department of Astronomy/Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
²⁵ Centre for Earth Evolution and Dynamics, Department of Geosciences, Universitetet i Oslo, Sem Sælands vei 2b, 0315 Oslo, Norway
²⁶ Department of Physics & Astronomy, University of California, Irvine, CA 92697, USA
²⁷ University of Colorado, Boulder Laboratory for Atmospheric and Space Physics, Department of Atmospheric and Oceanic Sciences, Boulder, CO 80303, USA
²⁸ NASA NExSS Virtual Planetary Laboratory, Seattle, WA, USA

Received: 28 October 2022
Accepted: 21 December 2022

Abstract

We present the discovery of an Earth-mass planet (M_b sin i = 1.26 ± 0.21 M_⊕) on a 15.6 d orbit of a relatively nearby (d ~ 9.6 pc) and low-mass (0.167 ± 0.011 M_⊙) M5.0 V star, Wolf 1069. Sitting at a separation of 0.0672 ± 0.0014 au away from the host star puts Wolf 1069 b in the habitable zone (HZ), receiving an incident flux of S = 0.652 ± 0.029 S_⊕. The planetary signal was detected using telluric-corrected radial-velocity (RV) data from the CARMENES spectrograph, amounting to a total of 262 spectroscopic observations covering almost four years. There are additional long-period signals in the RVs, one of which we attribute to the stellar rotation period. This is possible thanks to our photometric analysis including new, well-sampled monitoring campaigns undergone with the OSN and TJO facilities that supplement archival photometry (i.e., from MEarth and SuperWASP), and this yielded an updated rotational period range of P_rot = 150–170 d, with a likely value at 169.3_−3.6^+3.7. The stellar activity indicators provided by the CARMENES spectra likewise demonstrate evidence for the slow rotation period, though not as accurately due to possible factors such as signal aliasing or spot evolution. Our detectability limits indicate that additional planets more massive than one Earth mass with orbital periods of less than 10 days can be ruled out, suggesting that perhaps Wolf 1069 b had a violent formation history. This planet is also the sixth closest Earth-mass planet situated in the conservative HZ, after Proxima Centauri b, GJ 1061 d, Teegarden’s Star c, and GJ 1002 b and c. Despite not transiting, Wolf 1069 b is nonetheless a very promising target for future three-dimensional climate models to investigate various habitability cases as well as for sub-m s⁻¹ RV campaigns to search for potential inner sub-Earth-mass planets in order to test planet formation theories.