From thermal dissociation to condensation in the atmospheres of ultra hot Jupiters: WASP-121b in context

Context. A new class of exoplanets has emerged: the ultra hot Jupiters, the hottest close-in gas giants. The majority of them have weaker-than-expected spectral features in the 1.1−1.7 μm bandpass probed by HST/WFC3 but stronger spectral features at longer wavelengths probed by Spitzer. This led previous authors to puzzling conclusions about the thermal structures and chemical abundances of these planets. Aims. We investigate how thermal dissociation, ionization, H− opacity, and clouds shape the thermal structures and spectral properties of ultra hot Jupiters. Methods. We use the SPARC/MITgcm to model the atmospheres of four ultra hot Jupiters and discuss more thoroughly the case of WASP-121b. We expand our findings to the whole population of ultra hot Jupiters through analytical quantification of the thermal dissociation and its influence on the strength of spectral features. Results. We predict that most molecules are thermally dissociated and alkalies are ionized in the dayside photospheres of ultra hot Jupiters. This includes H2O, TiO, VO, and H2 but not CO, which has a stronger molecular bond. The vertical molecular gradient created by the dissociation significantly weakens the spectral features from H2O while the 4.5 μm CO feature remains unchanged. The water band in the HST/WFC3 bandpass is further weakened by the continuous opacity of the H− ions. Molecules are expected to recombine before reaching the limb, leading to order of magnitude variations of the chemical composition and cloud coverage between the limb and the dayside. Conclusions. Molecular dissociation provides a qualitative understanding of the lack of strong spectral features of water in the 1−2 μm bandpass observed in most ultra hot Jupiters. Quantitatively, our model does not provide a satisfactory match to the WASP-121b emission spectrum. Together with WASP-33b and Kepler-33Ab, they seem the outliers among the population of ultra hot Jupiters, in need of a more thorough understanding.

[1]  D. Crisp,et al.  A SYSTEMATIC RETRIEVAL ANALYSIS OF SECONDARY ECLIPSE SPECTRA. I. A COMPARISON OF ATMOSPHERIC RETRIEVAL TECHNIQUES , 2013, 1304.5561.

[2]  Jacob L. Bean,et al.  An Observational Diagnostic for Distinguishing between Clouds and Haze in Hot Exoplanet Atmospheres , 2017, 1705.05847.

[3]  L. Decin,et al.  Constraints on Metal Oxide and Metal Hydroxide Abundances in the Winds of AGB Stars: Potential Detection of FeO in R Dor , 2018, 1801.09302.

[4]  A. D. Etangs,et al.  Rayleigh scattering in the transit spectrum of HD 189733b , 2008, 0802.3228.

[5]  D. Deming,et al.  SPECTROSCOPIC EVIDENCE FOR A TEMPERATURE INVERSION IN THE DAYSIDE ATMOSPHERE OF HOT JUPITER WASP-33b , 2015, 1505.01490.

[6]  R. Poole,et al.  FINDING EXTRATERRESTRIAL LIFE USING GROUND-BASED HIGH-DISPERSION SPECTROSCOPY , 2013, 1302.3251.

[7]  Sara Seager,et al.  Thermal structure of an exoplanet atmosphere from phase-resolved emission spectroscopy , 2014, Science.

[8]  G. Bakos.  The HATNet and HATSouth Exoplanet Surveys , 2018, 1801.00849.

[9]  Michael R. Line,et al.  THE INFLUENCE OF NONUNIFORM CLOUD COVER ON TRANSIT TRANSMISSION SPECTRA , 2015, 1511.09443.

[10]  John Asher Johnson,et al.  THE FREQUENCY OF HOT JUPITERS ORBITING NEARBY SOLAR-TYPE STARS , 2012, 1205.2273.

[11]  Avi Shporer,et al.  Evidence for Atmospheric Cold-trap Processes in the Noninverted Emission Spectrum of Kepler-13Ab Using HST/WFC3 , 2016, 1612.06409.

[12]  Jonathan J. Fortney,et al.  The effect of condensates on the characterization of transiting planet atmospheres with transmission spectroscopy , 2005, astro-ph/0509292.

[13]  M. Marley,et al.  THREE-DIMENSIONAL ATMOSPHERIC CIRCULATION OF HOT JUPITERS ON HIGHLY ECCENTRIC ORBITS , 2010, 1208.3795.

[14]  T. Guillot,et al.  A non-grey analytical model for irradiated atmospheres - I. Derivation , 2013, 1311.6597.

[15]  A. Showman,et al.  ATMOSPHERIC HEAT REDISTRIBUTION ON HOT JUPITERS , 2013, 1306.4673.

[16]  A. Showman,et al.  Effects of Bulk Composition on the Atmospheric Dynamics on Close-in Exoplanets , 2014, 1607.04260.

[17]  K. Lodders.  Titanium and Vanadium Chemistry in Low-Mass Dwarf Stars , 2002 .

[18]  Mark S. Marley,et al.  Planetary Radii across Five Orders of Magnitude in Mass and Stellar Insolation: Application to Transits , 2006 .

[19]  David Charbonneau,et al.  ATMOSPHERIC CIRCULATION OF HOT JUPITERS: COUPLED RADIATIVE-DYNAMICAL GENERAL CIRCULATION MODEL SIMULATIONS OF HD 189733b and HD 209458b , 2008, 0809.2089.

[20]  Jacob L. Bean,et al.  A DETECTION OF WATER IN THE TRANSMISSION SPECTRUM OF THE HOT JUPITER WASP-12b AND IMPLICATIONS FOR ITS ATMOSPHERIC COMPOSITION , 2015, 1504.05586.

[21]  Nikole K. Lewis,et al.  An ultrahot gas-giant exoplanet with a stratosphere , 2017, Nature.

[22]  C P McKay,et al.  Thermal structure of Uranus' atmosphere. , 1999, Icarus.

[23]  K. Stassun,et al.  NEAR-INFRARED EMISSION SPECTRUM OF WASP-103B USING HUBBLE SPACE TELESCOPE/WIDE FIELD CAMERA 3 , 2016, 1611.09272.

[24]  A. P. Showman,et al.  The Influence of Atmospheric Dynamics on the Infrared Spectra and Light Curves of Hot Jupiters , 2006 .

[25]  A. Pannekoek.  The Theoretical Contours of Absorption Lines. (Second Paper.) , 1931 .

[26]  W. C. Bowman,et al.  A high C/O ratio and weak thermal inversion in the atmosphere of exoplanet WASP-12b , 2010, Nature.

[27]  Sara Seager,et al.  A PRECISE WATER ABUNDANCE MEASUREMENT FOR THE HOT JUPITER WASP-43b , 2014, 1410.2255.

[28]  A. Boccaletti,et al.  Interpreting the photometry and spectroscopy of directly imaged planets: a new atmospheric model applied to β Pictoris b and SPHERE observations , 2015, 1504.04876.

[29]  M. Marley,et al.  Line and Mean Opacities for Ultracool Dwarfs and Extrasolar Planets , 2007, 0706.2374.

[30]  J. Fortney,et al.  THE IMPACT OF NON-UNIFORM THERMAL STRUCTURE ON THE INTERPRETATION OF EXOPLANET EMISSION SPECTRA , 2016, 1607.03230.

[31]  P. A. R. Ade,et al.  EChO - Exoplanet Characterisation Observatory , 2010, 1112.2728.

[32]  R. J. de Kok,et al.  Carbon monoxide and water vapor in the atmosphere of the non-transiting exoplanet HD 179949 b , 2014, 1404.3769.

[33]  T. Komacek,et al.  Atmospheric Circulation of Hot Jupiters: Dayside–Nightside Temperature Differences. II. Comparison with Observations , 2016, 1610.03893.

[34]  Michael D. Smith,et al.  Planetary Spectrum Generator: An accurate online radiative transfer suite for atmospheres, comets, small bodies and exoplanets , 2018, Journal of Quantitative Spectroscopy and Radiative Transfer.

[35]  A. Santerne,et al.  WASP-121 b: a hot Jupiter in a polar orbit and close to tidal disruption , 2015, 1506.02471.

[36]  N. Cowan,et al.  Increased Heat Transport in Ultra-hot Jupiter Atmospheres through H2 Dissociation and Recombination , 2018, 1802.07725.

[37]  S. Chandrasekhar.  On the Continuous Absorption Coefficient of the Negative Hydrogen Ion. II. , 1945 .

[38]  Nikku Madhusudhan,et al.  NO THERMAL INVERSION AND A SOLAR WATER ABUNDANCE FOR THE HOT JUPITER HD 209458B FROM HST/WFC3 SPECTROSCOPY , 2016, 1605.08810.

[39]  T. Henning,et al.  MODEL ATMOSPHERES OF IRRADIATED EXOPLANETS: THE INFLUENCE OF STELLAR PARAMETERS, METALLICITY, AND THE C/O RATIO , 2015, 1509.07523.

[40]  B. Fegley,et al.  Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars. II. Sulfur and Phosphorus , 2005, astro-ph/0511136.

[41]  Drake Deming,et al.  ATMOSPHERIC CHARACTERIZATION OF FIVE HOT JUPITERS WITH THE WIDE FIELD CAMERA 3 ON THE HUBBLE SPACE TELESCOPE , 2014, 1403.1266.

[42]  Patrick G. J. Irwin,et al.  Optimal estimation retrievals of the atmospheric structure and composition of HD 189733b from secondary eclipse spectroscopy , 2011, 1110.2934.

[43]  Jacob L. Bean,et al.  THE ATMOSPHERIC CIRCULATION OF THE HOT JUPITER WASP-43b: COMPARING THREE-DIMENSIONAL MODELS TO SPECTROPHOTOMETRIC DATA , 2014, 1410.2382.

[44]  E. Salpeter,et al.  Rosseland and Planck mean opacities of a zero-metallicity gas , 1991 .

[45]  C. McKay,et al.  Rapid calculation of radiative heating rates and photodissociation rates in inhomogeneous multiple scattering atmospheres , 1989 .

[46]  Jacob L. Bean,et al.  An HST/WFC3 Thermal Emission Spectrum of the Hot Jupiter HAT-P-7b , 2018, The Astronomical Journal.

[47]  B. Fegley,et al.  ATMOSPHERIC CHEMISTRY IN GIANT PLANETS, BROWN DWARFS, AND LOW-MASS DWARF STARS. III. IRON, MAGNESIUM, AND SILICON , 2010, 1001.3639.

[48]  Drake Deming,et al.  Evidence for a Dayside Thermal Inversion and High Metallicity for the Hot Jupiter WASP-18b , 2017, 1711.10491.

[49]  Chemistry of the Earth's Earliest Atmosphere , 2012, 1210.0270.

[50]  S. Seager,et al.  Clouds and chemistry: Ultracool dwarf atmospheric properties from optical and infrared colors , 2002 .

[51]  J. Bean,et al.  DECIPHERING THE ATMOSPHERIC COMPOSITION OF WASP-12b: A COMPREHENSIVE ANALYSIS OF ITS DAYSIDE EMISSION , 2014, 1406.7567.

[52]  J. Manners,et al.  The effect of metallicity on the atmospheres of exoplanets with fully coupled 3D hydrodynamics, equilibrium chemistry, and radiative transfer (dataset) , 2018, 1801.01045.

[53]  I. Hubeny,et al.  A Possible Bifurcation in Atmospheres of Strongly Irradiated Stars and Planets , 2003 .

[54]  B. Fegley,et al.  Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars: I. Carbon, Nitrogen, and Oxygen , 2002 .

[55]  S. Seager,et al.  ON THE INFERENCE OF THERMAL INVERSIONS IN HOT JUPITER ATMOSPHERES , 2010, 1010.4585.

[56]  T. Komacek,et al.  ATMOSPHERIC CIRCULATION OF HOT JUPITERS: DAYSIDE–NIGHTSIDE TEMPERATURE DIFFERENCES , 2016, 1601.00069.

[57]  M. Marley,et al.  High-temperature condensate clouds in super-hot Jupiter atmospheres , 2016, 1610.03325.

[58]  Richard W. Pogge,et al.  The Kilodegree Extremely Little Telescope (KELT): A Small Robotic Telescope for Large‐Area Synoptic Surveys , 2007, 0704.0460.

[59]  Marcell Tessenyi,et al.  Probing the extreme planetary atmosphere of WASP-12b , 2012, 1205.4736.

[60]  R. Wildt.  Negative Ions of Hydrogen and the Opacity of Stellar Atmospheres. , 1939 .

[61]  Y. Yung,et al.  Atmospheric Radiation: Theoretical Basis , 1989 .

[62]  D. Ehrenreich,et al.  Hubble PanCET: an isothermal day-side atmosphere for the bloated gas-giant HAT-P-32Ab , 2017, 1711.00859.

[63]  Sun Mi Chung,et al.  The Broadband and Spectrally Resolved H-band Eclipse of KELT-1b and the Role of Surface Gravity in Stratospheric Inversions in Hot Jupiters , 2016, 1610.03504.

[64]  Drake Deming,et al.  THE EMERGENT 1.1–1.7 μm SPECTRUM OF THE EXOPLANET COROT-2B AS MEASURED USING THE HUBBLE SPACE TELESCOPE , 2014, 1401.4464.

[65]  P. Roth,et al.  HIGH-TEMPERATURE KINETICS OF SI + N2O , 1994 .

[66]  A. Santerne,et al.  WASP-121 b: a hot Jupiter close to tidal disruption transiting an active F star , 2015, 1506.02471.

[67]  T. Guillot,et al.  A non-grey analytical model for irradiated atmospheres - II. Analytical vs. numerical solutions , 2013, 1311.6322.

[68]  Gerd Weigelt,et al.  THE LEECH EXOPLANET IMAGING SURVEY: CHARACTERIZATION OF THE COLDEST DIRECTLY IMAGED EXOPLANET, GJ 504 b, AND EVIDENCE FOR SUPERSTELLAR METALLICITY , 2015, 1511.09183.

[69]  A. Showman,et al.  3D mixing in hot Jupiters atmospheres. I. Application to the day/night cold trap in HD 209458b , 2013, 1301.4522.

[70]  Sara Seager,et al.  Constraining Exoplanet Mass from Transmission Spectroscopy , 2013, Science.

[71]  T. Barman,et al.  COMPOSITIONAL DIVERSITY IN THE ATMOSPHERES OF HOT NEPTUNES, WITH APPLICATION TO GJ 436b , 2013, The Astrophysical journal.

[72]  M. Marley,et al.  THE ATMOSPHERIC CIRCULATION OF A NINE-HOT-JUPITER SAMPLE: PROBING CIRCULATION AND CHEMISTRY OVER A WIDE PHASE SPACE , 2016, 1602.06733.

[73]  Accuracy tests of radiation schemes used in hot Jupiter global circulation models , 2014, 1402.0814.

[74]  James Liebert,et al.  M dwarf spectra from 0.6 to 1.5 micron - A spectral sequence, model atmosphere fitting, and the temperature scale , 1993 .

[75]  Adam Burrows,et al.  CAN TiO EXPLAIN THERMAL INVERSIONS IN THE UPPER ATMOSPHERES OF IRRADIATED GIANT PLANETS? , 2009, 0902.3995.

[76]  Vivien Parmentier,et al.  TRANSITIONS IN THE CLOUD COMPOSITION OF HOT JUPITERS , 2016, 1602.03088.

[77]  N. Crouzet,et al.  Water Vapor in the Spectrum of the Extrasolar Planet HD 189733b. II. The Eclipse , 2014, 1409.4000.

[78]  Richard S. Freedman,et al.  A Unified Theory for the Atmospheres of the Hot and Very Hot Jupiters: Two Classes of Irradiated Atmospheres , 2007, 0710.2558.

[79]  T. Guillot,et al.  Atmospheric, Evolutionary, and Spectral Models of the Brown Dwarf Gliese 229 B , 1996, Science.

[80]  Jacob L. Bean,et al.  H− Opacity and Water Dissociation in the Dayside Atmosphere of the Very Hot Gas Giant WASP-18b , 2018, 1801.02489.

[81]  T. Evans,et al.  DETECTION OF H2O AND EVIDENCE FOR TiO/VO IN AN ULTRA-HOT EXOPLANET ATMOSPHERE , 2016, 1604.02310.

[82]  E. Agol,et al.  Phase Curves of WASP-33b and HD 149026b and a New Correlation between Phase Curve Offset and Irradiation Temperature , 2017, 1710.07642.

[83]  Gilles Chabrier,et al.  FINGERING CONVECTION AND CLOUDLESS MODELS FOR COOL BROWN DWARF ATMOSPHERES , 2015, 1504.03334.

[84]  M. Marley,et al.  GASEOUS MEAN OPACITIES FOR GIANT PLANET AND ULTRACOOL DWARF ATMOSPHERES OVER A RANGE OF METALLICITIES AND TEMPERATURES , 2014, 1409.0026.

[85]  Peter H. Hauschildt,et al.  Irradiated planets , 2001, astro-ph/0104262.

[86]  A. P. Showman,et al.  TRANSMISSION SPECTRA OF THREE-DIMENSIONAL HOT JUPITER MODEL ATMOSPHERES , 2009, 0912.2350.

[87]  D. Saumon,et al.  Retrieval of atmospheric properties of cloudy L dwarfs , 2017, 1701.01257.

[88]  Jacob L. Bean,et al.  Global Climate and Atmospheric Composition of the Ultra-hot Jupiter WASP-103b from HST and Spitzer Phase Curve Observations , 2018, The Astronomical Journal.

[89]  T. Guillot,et al.  A Nongray Theory of Extrasolar Giant Planets and Brown Dwarfs , 1997, astro-ph/9705201.

[90]  T. Evans,et al.  The Very Low Albedo of WASP-12b from Spectral Eclipse Observations with Hubble , 2017, 1709.04461.

[91]  S. Seager,et al.  A TEMPERATURE AND ABUNDANCE RETRIEVAL METHOD FOR EXOPLANET ATMOSPHERES , 2009, 0910.1347.

[92]  P. Magain,et al.  High-precision multiwavelength eclipse photometry of the ultra-hot gas giant exoplanet WASP-103 b , 2017, 1711.02566.

[93]  B. Enoch,et al.  The WASP Project and the SuperWASP Cameras , 2006, astro-ph/0608454.

[94]  V. Oinas,et al.  Atmospheric Radiation , 1963, Nature.

[95]  C. McKay,et al.  The thermal structure of Titan's atmosphere. , 1989, Icarus.

[96]  Tristan Guillot,et al.  Atmospheric circulation and tides of ``51 Pegasus b-like'' planets , 2002 .