title: A map of the large day-night temperature gradient of a super-Earth exoplanet.
abstract: Over the past decade, observations of giant exoplanets (Jupiter-size) have provided key insights into their atmospheres, but the properties of lower-mass exoplanets (sub-Neptune) remain largely unconstrained because of the challenges of observing small planets. Numerous efforts to observe the spectra of super-Earths--exoplanets with masses of one to ten times that of Earth--have so far revealed only featureless spectra. Here we report a longitudinal thermal brightness map of the nearby transiting super-Earth 55 Cancri e (refs 4, 5) revealing highly asymmetric dayside thermal emission and a strong day-night temperature contrast. Dedicated space-based monitoring of the planet in the infrared revealed a modulation of the thermal flux as 55 Cancri e revolves around its star in a tidally locked configuration. These observations reveal a hot spot that is located 41 ± 12 degrees east of the substellar point (the point at which incident light from the star is perpendicular to the surface of the planet). From the orbital phase curve, we also constrain the nightside brightness temperature of the planet to 1,380 ± 400 kelvin and the temperature of the warmest hemisphere (centred on the hot spot) to be about 1,300 kelvin hotter (2,700 ± 270 kelvin) at a wavelength of 4.5 micrometres, which indicates inefficient heat redistribution from the dayside to the nightside. Our observations are consistent with either an optically thick atmosphere with heat recirculation confined to the planetary dayside, or a planet devoid of atmosphere with low-viscosity magma flows at the surface.
authors.affiliation: Astrophysics Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: Brice-Olivier
authors.initials: BO
authors.lastname: Demory
authors.affiliation: Institut d'Astrophysique et de Géophysique, Université of Liège, allée du 6 Aout 17, 4000 Liège, Belgium.
authors.forename: Michael
authors.initials: M
authors.lastname: Gillon
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: Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK.
authors.forename: Nikku
authors.initials: N
authors.lastname: Madhusudhan
authors.affiliation: NaXys, Department of Mathematics, University of Namur, 8 Rempart de la Vierge, 5000 Namur, Belgium.
authors.forename: Emeline
authors.initials: E
authors.lastname: Bolmont
authors.affiliation: University of Bern, Center for Space and Habitability, Sidlerstrasse 5, CH-3012, Bern, Switzerland.
authors.forename: Kevin
authors.initials: K
authors.lastname: Heng
authors.affiliation: Astrophysics Group, School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK.
authors.forename: Tiffany
authors.initials: T
authors.lastname: Kataria
authors.affiliation: Space Telescope Science Institute, Baltimore, Maryland 21218, USA.
authors.forename: Nikole
authors.initials: N
authors.lastname: Lewis
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA.|Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Renyu
authors.initials: R
authors.lastname: Hu
authors.affiliation: Spitzer Science Center, MS 220-6, California Institute of Technology, Jet Propulsion Laboratory, Pasadena, California 91125, USA.
authors.forename: Jessica
authors.initials: J
authors.lastname: Krick
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA.|Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Vlada
authors.initials: V
authors.lastname: Stamenković
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Björn
authors.initials: B
authors.lastname: Benneke
authors.affiliation: Department of Physics and Astronomy, San Francisco State University, 1600 Holloway Avenue, San Francisco, California 94132, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Kane
authors.affiliation: Astrophysics Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: Didier
authors.initials: D
authors.lastname: Queloz