title: A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion.
abstract: Thousands of transiting exoplanets have been discovered, but spectral analysis of their atmospheres has so far been dominated by a small number of exoplanets and data spanning relatively narrow wavelength ranges (such as 1.1-1.7 micrometres). Recent studies show that some hot-Jupiter exoplanets have much weaker water absorption features in their near-infrared spectra than predicted. The low amplitude of water signatures could be explained by very low water abundances, which may be a sign that water was depleted in the protoplanetary disk at the planet's formation location, but it is unclear whether this level of depletion can actually occur. Alternatively, these weak signals could be the result of obscuration by clouds or hazes, as found in some optical spectra. Here we report results from a comparative study of ten hot Jupiters covering the wavelength range 0.3-5 micrometres, which allows us to resolve both the optical scattering and infrared molecular absorption spectroscopically. Our results reveal a diverse group of hot Jupiters that exhibit a continuum from clear to cloudy atmospheres. We find that the difference between the planetary radius measured at optical and infrared wavelengths is an effective metric for distinguishing different atmosphere types. The difference correlates with the spectral strength of water, so that strong water absorption lines are seen in clear-atmosphere planets and the weakest features are associated with clouds and hazes. This result strongly suggests that primordial water depletion during formation is unlikely and that clouds and hazes are the cause of weaker spectral signatures.
authors.affiliation: Astrophysics Group, School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK.
authors.forename: David K
authors.initials: DK
authors.lastname: Sing
authors.affiliation: Department of Astronomy and Astrophysics, University of California, Santa Cruz, California 95064, USA.
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Fortney
authors.affiliation: Astrophysics Group, School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK.
authors.forename: Nikolay
authors.initials: N
authors.lastname: Nikolov
authors.affiliation: Astrophysics Group, School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK.
authors.forename: Hannah R
authors.initials: HR
authors.lastname: Wakeford
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: Astrophysics Group, School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Evans
authors.affiliation: Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Aigrain
authors.affiliation: Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Gilda E
authors.initials: GE
authors.lastname: Ballester
authors.affiliation: Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Adam S
authors.initials: AS
authors.lastname: Burrows
authors.affiliation: Department of Astronomy, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Drake
authors.initials: D
authors.lastname: Deming
authors.affiliation: Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Désert
authors.affiliation: European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Munchen, Germany.
authors.forename: Neale P
authors.initials: NP
authors.lastname: Gibson
authors.affiliation: Center of Excellence in Information Systems, Tennessee State University, Nashville, Tennessee 37209, USA.
authors.forename: Gregory W
authors.initials: GW
authors.lastname: Henry
authors.affiliation: Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Huitson
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Heather A
authors.initials: HA
authors.lastname: Knutson
authors.affiliation: CNRS, Institut dAstrophysique de Paris, UMR 7095, 98 bis boulevard Arago, 75014 Paris, France.
authors.forename: Alain Lecavelier
authors.initials: AL
authors.lastname: des Etangs
authors.affiliation: Astrophysics Group, School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK.
authors.forename: Frederic
authors.initials: F
authors.lastname: Pont
authors.affiliation: Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Adam P
authors.initials: AP
authors.lastname: Showman
authors.affiliation: CNRS, Institut dAstrophysique de Paris, UMR 7095, 98 bis boulevard Arago, 75014 Paris, France.
authors.forename: Alfred
authors.initials: A
authors.lastname: Vidal-Madjar
authors.affiliation: Center of Excellence in Information Systems, Tennessee State University, Nashville, Tennessee 37209, USA.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Williamson
authors.affiliation: CNRS, Institut dAstrophysique de Paris, UMR 7095, 98 bis boulevard Arago, 75014 Paris, France.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Wilson
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D005118:Extraterrestrial Environment / Q000737:chemistry*; D018538:Jupiter; D016083:Planets; D011312:Pressure; D013055:Spectrophotometry, Infrared; D061351:Telescopes; D013696:Temperature; D014867:Water / Q000032:analysis*
chemical_list: D014867:Water