Wavelength Does Not Equal Pressure: Vertical Contribution Functions and their Implications for Mapping Hot Jupiters

Abstract

Multi-band phase variations in principle allow us to infer the longitudinal temperature distributions of planets as a function of height in their atmospheres. For example, 3.6 micron emission originates from deeper layers of the atmosphere than 4.5 micron due to greater water vapor absorption at the longer wavelength. Since heat transport efficiency increases with pressure, we expect thermal phase curves at 3.6 micron to exhibit smaller amplitudes and greater phase offsets than at 4.5 micron; this trend is not observed. Of the seven hot Jupiters with full-orbit phase curves at 3.6 and 4.5 micron, all have greater phase amplitude at 3.6 micron than at 4.5 micron, while four of seven exhibit a greater phase offset at 3.6 micron. We use a 3D radiative-hydrodynamic model to calculate theoretical phase curves of HD 189733b, assuming thermo-chemical equilibrium. The model exhibits temperature, pressure, and wavelength dependent opacity, primarily driven by carbon chemistry: CO is energetically favored on the dayside, while CH4 is favored on the cooler nightside. Infrared opacity therefore changes by orders of magnitude between day and night, producing dramatic vertical shifts in the wavelength-specific photospheres, which would complicate eclipse or phase mapping with spectral data. The model predicts greater relative phase amplitude and greater phase offset at 3.6 micron than at 4.5 micron, in agreement with the data. Our model qualitatively explains the observed phase curves, but is in tension with current thermo-chemical kinetics models that predict zonally uniform atmospheric composition due to transport of CO from the hot regions of the atmosphere.

9 pages, 5 figures, accepted for publications in ApJ Letters

References in corpus (14)

• Thermal structure of an exoplanet atmosphere from phase-resolved emission spectroscopy
• Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres
• Possible thermochemical disequilibrium in the atmosphere of the exoplanet GJ 436b
• A giant planet undergoing extreme ultraviolet irradiation by its hot massive-star host
• Multi-Wavelength Constraints on the Day-Night Circulation Patterns of HD 189733b
• Dynamics and Disequilibrium Carbon Chemistry in Hot Jupiter Atmospheres, With Application to HD 209458b
• Inverting Phase Functions to Map Exoplanets
• Changing Phases of Alien Worlds: Probing Atmospheres of Kepler Planets with High-Precision Photometry
• Atmospheric Dynamics of Hot Exoplanets
• Spitzer Phase Curve Constraints for WASP-43b at 3.6 and 4.5 microns
• Pseudo 2D chemical model of hot Jupiter atmospheres: application to HD 209458b and HD 189733b
• Balancing the Energy Budget of Short-Period Giant Planets: Evidence for Reflective Clouds and Optical Absorbers
• 3D Structures of equatorial waves and the resulting superrotation in the atmosphere of a tidally locked hot Jupiter
• Effects of Bulk Composition on The Atmospheric Dynamics on Close-in Exoplanets