TY - JOUR
T1 - Beyond Equilibrium Temperature
T2 - How the Atmosphere/Interior Connection Affects the Onset of Methane, Ammonia, and Clouds in Warm Transiting Giant Planets
AU - Fortney, Jonathan J.
AU - Visscher, Channon
AU - Marley, Mark S.
AU - Hood, Callie E.
AU - Line, Michael R.
AU - Thorngren, Daniel P.
AU - Freedman, Richard S.
AU - Lupu, Roxana
N1 - Publisher Copyright:
© 2020. The American Astronomical Society. All rights reserved..
PY - 2020/12
Y1 - 2020/12
N2 - The atmospheric pressureerature profiles for transiting giant planets cross a range of chemical transitions. Here we show that the particular shapes of these irradiated profiles for warm giant planets below ∼1300 K lead to striking differences in the behavior of nonequilibrium chemistry compared to brown dwarfs of similar temperatures. Our particular focus is H2O, CO, CH4, CO2, and NH3 in Jupiter- and Neptune-class planets. We show that the cooling history of a planet, which depends most significantly on planetary mass and age, can have a dominant effect on abundances in the visible atmosphere, often swamping trends one might expect based on T eq alone. The onset of detectable CH4 in spectra can be delayed to lower T eq for some planets compared to equilibrium, or pushed to higher T eq. The detectability of NH3 is typically enhanced compared to equilibrium expectations, which is opposite to the brown dwarf case. We find that both CH4 and NH3 can become detectable at around the same T eq (at T eq values that vary with mass and metallicity), whereas these "onset"temperatures are widely spaced for brown dwarfs. We suggest observational strategies to search for atmospheric trends and stress that nonequilibrium chemistry and clouds can serve as probes of atmospheric physics. As examples of atmospheric complexity, we assess three Neptune-class planets, GJ 436b, GJ 3470b, and WASP-107, all around T eq = 700 K. Tidal heating due to eccentricity damping in all three planets heats the deep atmosphere by thousands of degrees and may explain the absence of CH4 in these cool atmospheres. Atmospheric abundances must be interpreted in the context of physical characteristics of the planet.
AB - The atmospheric pressureerature profiles for transiting giant planets cross a range of chemical transitions. Here we show that the particular shapes of these irradiated profiles for warm giant planets below ∼1300 K lead to striking differences in the behavior of nonequilibrium chemistry compared to brown dwarfs of similar temperatures. Our particular focus is H2O, CO, CH4, CO2, and NH3 in Jupiter- and Neptune-class planets. We show that the cooling history of a planet, which depends most significantly on planetary mass and age, can have a dominant effect on abundances in the visible atmosphere, often swamping trends one might expect based on T eq alone. The onset of detectable CH4 in spectra can be delayed to lower T eq for some planets compared to equilibrium, or pushed to higher T eq. The detectability of NH3 is typically enhanced compared to equilibrium expectations, which is opposite to the brown dwarf case. We find that both CH4 and NH3 can become detectable at around the same T eq (at T eq values that vary with mass and metallicity), whereas these "onset"temperatures are widely spaced for brown dwarfs. We suggest observational strategies to search for atmospheric trends and stress that nonequilibrium chemistry and clouds can serve as probes of atmospheric physics. As examples of atmospheric complexity, we assess three Neptune-class planets, GJ 436b, GJ 3470b, and WASP-107, all around T eq = 700 K. Tidal heating due to eccentricity damping in all three planets heats the deep atmosphere by thousands of degrees and may explain the absence of CH4 in these cool atmospheres. Atmospheric abundances must be interpreted in the context of physical characteristics of the planet.
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U2 - 10.3847/1538-3881/abc5bd
DO - 10.3847/1538-3881/abc5bd
M3 - Article
AN - SCOPUS:85102078000
SN - 0004-6256
VL - 160
JO - Astronomical Journal
JF - Astronomical Journal
IS - 6
M1 - 288
ER -