Planetary system around the nearby M dwarf GJ 357 including a transiting, hot, Earth-sized planet optimal for atmospheric characterization^★

¹ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
e-mail: rluque@iac.es
² Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁵ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
⁶ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁷ School of Physics and Astronomy, Queen Mary University of London, 327 Mile End Road, London, E1 4NS, UK
⁸ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁹ Centro de Astrobiología (CSIC-INTA), ESAC, Camino bajo del castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
¹⁰ Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138, USA
¹¹ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA
¹² Departamento de Física de la Tierra y Astrofísica & IPARCOS-UCM (Instituto de Física de Partículas y del Cosmos de la UCM), Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
¹³ Department of Exploitation and Exploration of Mines, University of Oviedo, Oviedo, Spain
¹⁴ Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road, NW, Washington, DC 20015, USA
¹⁵ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹⁶ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
¹⁷ Carl Sagan Institute, Cornell University, Ithaca, NY 14853, USA
¹⁸ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁹ JST, PRESTO, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²⁰ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²¹ Weizmann Institute of Science, 234 Herzl Street, Rehovot 761001, Israel
²² Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA
²³ Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
²⁴ Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
²⁵ SETI Institute, Mountain View, CA 94043, USA
²⁶ NASA Ames Research Center, Moffett Field, CA 94035, USA
²⁷ Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, PR China
²⁸ Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101, USA
²⁹ Department of Astronomy, The University of California, Berkeley, CA 94720, USA
³⁰ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, C/Can Magrans s/n, 08193 Bellaterra, Spain
³¹ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
³² The Maury Lewin Astronomical Observatory, Glendora, California 91741, USA
³³ Proto-Logic LLC, 1718 Euclid Street NW, Washington, DC 20009, USA
³⁴ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
³⁵ Centro Astronómico Hispano-Alemán (CSIC-MPG), Observatorio Astronómico de Calar Alto, Sierra de los Filabres-04550 Gérgal, Almería, Spain
³⁶ School of Physical Sciences, The Open University, Milton Keynes MK7 6AA, UK
³⁷ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
³⁸ Department of Aeronautics and Astronautics, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
³⁹ Department of Astronomy, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Received: 29 April 2019
Accepted: 27 June 2019

Abstract

We report the detection of a transiting Earth-size planet around GJ 357, a nearby M2.5 V star, using data from the Transiting Exoplanet Survey Satellite (TESS). GJ 357 b (TOI-562.01) is a transiting, hot, Earth-sized planet (T_eq = 525 ± 11 K) with a radius of R_b = 1.217 ± 0.084 R_⊕ and an orbital period of P_b = 3.93 d. Precise stellar radial velocities from CARMENES and PFS, as well as archival data from HIRES, UVES, and HARPS also display a 3.93-day periodicity, confirming the planetary nature and leading to a planetary mass of M_b = 1.84 ± 0.31 M_⊕. In addition to the radial velocity signal for GJ 357 b, more periodicities are present in the data indicating the presence of two further planets in the system: GJ 357 c, with a minimum mass of M_c = 3.40 ± 0.46 M_⊕ in a 9.12 d orbit, and GJ 357 d, with a minimum mass of M_d = 6.1 ± 1.0 M_⊕ in a 55.7 d orbit inside the habitable zone. The host is relatively inactive and exhibits a photometric rotation period of P_rot = 78 ± 2 d. GJ 357 b isto date the second closest transiting planet to the Sun, making it a prime target for further investigations such as transmission spectroscopy. Therefore, GJ 357 b represents one of the best terrestrial planets suitable for atmospheric characterization with the upcoming JWST and ground-based ELTs.