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

Vivien Parmentier, Mike R. Line, Jacob L. Bean, Megan Mansfield, Laura Kreidberg, Roxana Lupu, Channon Visscher, Jean Michel Désert, Jonathan J. Fortney, Magalie Deleuil, Jacob Arcangeli, Adam Showman, Mark S. Marley

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

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.

Original languageEnglish (US)
Article numberA110
JournalAstronomy and Astrophysics
Volume617
DOIs
StatePublished - Sep 1 2018

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thermal dissociation
Jupiter (planet)
Jupiter
condensation
atmospheres
atmosphere
thermal structure
opacity
limbs
limb
chemical clouds
dissociation
extrasolar planets
photosphere
chemical bonds
outlier
water
molecules
planets
alkalies

Keywords

  • Planets and satellites: atmospheres
  • Planets and satellites: gaseous planets
  • Radiative transfer

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Parmentier, V., Line, M. R., Bean, J. L., Mansfield, M., Kreidberg, L., Lupu, R., ... Marley, M. S. (2018). From thermal dissociation to condensation in the atmospheres of ultra hot Jupiters: WASP-121b in context. Astronomy and Astrophysics, 617, [A110]. https://doi.org/10.1051/0004-6361/201833059

From thermal dissociation to condensation in the atmospheres of ultra hot Jupiters : WASP-121b in context. / Parmentier, Vivien; Line, Mike R.; Bean, Jacob L.; Mansfield, Megan; Kreidberg, Laura; Lupu, Roxana; Visscher, Channon; Désert, Jean Michel; Fortney, Jonathan J.; Deleuil, Magalie; Arcangeli, Jacob; Showman, Adam; Marley, Mark S.

In: Astronomy and Astrophysics, Vol. 617, A110, 01.09.2018.

Research output: Contribution to journalArticle

Parmentier, V, Line, MR, Bean, JL, Mansfield, M, Kreidberg, L, Lupu, R, Visscher, C, Désert, JM, Fortney, JJ, Deleuil, M, Arcangeli, J, Showman, A & Marley, MS 2018, 'From thermal dissociation to condensation in the atmospheres of ultra hot Jupiters: WASP-121b in context', Astronomy and Astrophysics, vol. 617, A110. https://doi.org/10.1051/0004-6361/201833059
Parmentier, Vivien ; Line, Mike R. ; Bean, Jacob L. ; Mansfield, Megan ; Kreidberg, Laura ; Lupu, Roxana ; Visscher, Channon ; Désert, Jean Michel ; Fortney, Jonathan J. ; Deleuil, Magalie ; Arcangeli, Jacob ; Showman, Adam ; Marley, Mark S. / From thermal dissociation to condensation in the atmospheres of ultra hot Jupiters : WASP-121b in context. In: Astronomy and Astrophysics. 2018 ; Vol. 617.
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abstract = "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.",
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AU - Line, Mike R.

AU - Bean, Jacob L.

AU - Mansfield, Megan

AU - Kreidberg, Laura

AU - Lupu, Roxana

AU - Visscher, Channon

AU - Désert, Jean Michel

AU - Fortney, Jonathan J.

AU - Deleuil, Magalie

AU - Arcangeli, Jacob

AU - Showman, Adam

AU - Marley, Mark S.

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N2 - 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.

AB - 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.

KW - Planets and satellites: atmospheres

KW - Planets and satellites: gaseous planets

KW - Radiative transfer

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