title: Temperate Earth-sized planets transiting a nearby ultracool dwarf star.
abstract: Star-like objects with effective temperatures of less than 2,700 kelvin are referred to as 'ultracool dwarfs'. 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. Core-accretion theory predicts that, given the small masses of these ultracool dwarfs, and the small sizes of their protoplanetary disks, there should be a large but hitherto undetected population of terrestrial planets orbiting them--ranging from metal-rich Mercury-sized planets to more hospitable volatile-rich Earth-sized planets. 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. 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.
authors.affiliation: Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium.
authors.forename: Michaël
authors.initials: M
authors.lastname: Gillon
authors.affiliation: Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium.
authors.forename: Emmanuël
authors.initials: E
authors.lastname: Jehin
authors.affiliation: NASA Johnson Space Center, 2101 NASA Parkway, Houston, Texas, 77058, USA.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Lederer
authors.affiliation: Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium.
authors.forename: Laetitia
authors.initials: L
authors.lastname: Delrez
authors.affiliation: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: Julien
authors.initials: J
authors.lastname: de Wit
authors.affiliation: Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium.
authors.forename: Artem
authors.initials: A
authors.lastname: Burdanov
authors.affiliation: Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium.
authors.forename: Valérie
authors.initials: V
authors.lastname: Van Grootel
authors.affiliation: Center for Astrophysics and Space Science, University of California San Diego, La Jolla, California 92093, USA.
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Burgasser
authors.affiliation: Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK.
authors.forename: Amaury H M J
authors.initials: AH
authors.lastname: Triaud
authors.affiliation: Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium.
authors.forename: Cyrielle
authors.initials: C
authors.lastname: Opitom
authors.affiliation: Astrophysics Group, Cavendish Laboratory, 19 J J Thomson Avenue, Cambridge, CB3 0HE, UK.
authors.forename: Brice-Olivier
authors.initials: BO
authors.lastname: Demory
authors.affiliation: Indian Institute of Astrophysics, Koramangala, Bangalore 560 034, India.
authors.forename: Devendra K
authors.initials: DK
authors.lastname: Sahu
authors.affiliation: Center for Astrophysics and Space Science, University of California San Diego, La Jolla, California 92093, USA.
authors.forename: Daniella
authors.initials: D
authors.lastname: Bardalez Gagliuffi
authors.affiliation: Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium.
authors.forename: Pierre
authors.initials: P
authors.lastname: Magain
authors.affiliation: Astrophysics Group, Cavendish Laboratory, 19 J J Thomson Avenue, Cambridge, CB3 0HE, UK.
authors.forename: Didier
authors.initials: D
authors.lastname: Queloz