Temperate Earth-sized planets transiting a nearby ultracool dwarf star

• Published in: Nature (London) Vol. 533; no. 7602; pp. 221 - 224
• Main Authors: Gillon, Michaël, Jehin, Emmanuël, Lederer, Susan M., Delrez, Laetitia, de Wit, Julien, Burdanov, Artem, Van Grootel, Valérie, Burgasser, Adam J., Triaud, Amaury H. M. J., Opitom, Cyrielle, Demory, Brice-Olivier, Sahu, Devendra K., Bardalez Gagliuffi, Daniella, Magain, Pierre, Queloz, Didier
• Format: Journal Article Web Resource
• Language: English
• Published: London Nature Publishing Group UK 12.05.2016; Nature Publishing Group
• Subjects: 639/33/34/862; 639/33/445/862; Accretion; Aérospatiale, astronomie & astrophysique; Dwarf stars; Earth; Humanities and Social Sciences; Irradiation; letter; Mercury; multidisciplinary; Observations; Orbits; Physical, chemical, mathematical & earth Sciences; Physique, chimie, mathématiques & sciences de la terre; Planets; Science; Space science, astronomy & astrophysics; Space telescopes; Spectrum analysis; Stars
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/nature17448

Three Earth-sized planets—receiving similar irradiation to Venus and Earth, and ideally suited for atmospheric study—have been found transiting a nearby ultracool dwarf star that has a mass of only eight per cent of that of the Sun. Three planets to watch Theory predicts that terrestrial or rocky planets are likely to be orbiting the lowest-mass stars. This paper reports the detection of a system of three Earth-sized planets transiting a very nearby (12 parsec) ultracool dwarf star of only 8% of the mass of the Sun. The planets are similar in irradiation to Venus and Earth, and particularly well suited for detailed atmospheric characterization. Star-like objects with effective temperatures of less than 2,700 kelvin are referred to as ‘ultracool dwarfs’ 1 . This heterogeneous group includes stars of extremely low mass as well as brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion), and represents about 15 per cent of the population of astronomical objects near the Sun 2 . Core-accretion theory predicts that, given the small masses of these ultracool dwarfs, and the small sizes of their protoplanetary disks 3 , 4 , there should be a large but hitherto undetected population of terrestrial planets orbiting them 5 —ranging from metal-rich Mercury-sized planets 6 to more hospitable volatile-rich Earth-sized planets 7 . Here we report observations of three short-period Earth-sized planets transiting an ultracool dwarf star only 12 parsecs away. The inner two planets receive four times and two times the irradiation of Earth, respectively, placing them close to the inner edge of the habitable zone of the star 8 . Our data suggest that 11 orbits remain possible for the third planet, the most likely resulting in irradiation significantly less than that received by Earth. The infrared brightness of the host star, combined with its Jupiter-like size, offers the possibility of thoroughly characterizing the components of this nearby planetary system.