Photochemistry in Hot H<sub>2</sub>-dominated Exoplanet Atmospheres

Fleury, Benjamin; Gudipati, Murthy S.; Henderson, Bryana L.; Swain, Mark R.

doi:10.3847/1538-4357/aaf79f

Cited by 55 publications

(173 citation statements)

References 71 publications

(91 reference statements)

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“…Common organic molecules are not stable at very high temperature (>1000 K, Johns et al 1962, Smay 1985, so we would not necessarily expect significant organic haze in the atmospheres of Jupiters hotter than 1000 K. This is consistent with a recent modeling study (Gao et al 2020), which found that aerosol composition is dominated by silicates for hot giant exoplanets with planetary equilibrium temperatures above 950 K, while is dominated by hydrocarbon aerosols below 950 K. However, it is possible to form organic hazes at temperatures above 1000 K as reported by Fleury et al (2019) who found that photochemistry can lead to the formation of an organic solid condensate at 1500K. We also need to consider that temperatures on the night sides of these hot planets can be significantly lower than on the day side, so there may be situations where gases that are photochemically produced on the day side are transported by winds to the night side, where they can form condensates.…”

Section: Haze Production Ratesupporting

confidence: 90%

“…The higher production rate without CH4 indicates that CH4 is neither required to generate organic hazes nor necessary to promote the organic haze formation. CO and/or CO2 can serve as a carbon source for haze formation (Fleury et al 2017(Fleury et al , 2019He et al 2018aHe et al , 2018bHe et al , 2019He et al , 2020Hörst et al 2018b;Moran et al 2020).…”

Section: Haze Production Ratementioning

confidence: 99%

“…Laboratory experimental simulations have advanced our understanding of haze formation in planetary atmospheres in the Solar System, e.g., Titan (Cable et al 2012). Such simulations can also probe photochemistry in exoplanet atmospheres (He et al 2018a(He et al , 2018b(He et al , 2019Hörst et al 2018a;Berry et al 2019b;Fleury et al 2019;Moran et al 2020).…”

Section: Introductionmentioning

confidence: 99%

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Sulfur-driven haze formation in warm CO2-rich exoplanet atmospheres

He¹,

Hörst²,

Lewis³

et al. 2020

Nat Astron

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Sulfur gases significantly affect the photochemistry of planetary atmospheres in ourSolar System, and are expected to be important components in exoplanet atmospheres. However, sulfur photochemistry in the context of exoplanets is poorly understood due to a lack of chemical-kinetics information for sulfur species under relevant conditions.Here, we study the photochemical role of hydrogen sulfide (H2S) in warm CO2-rich exoplanet atmospheres (800 K) by carrying out laboratory simulations. We find that H2S plays a significant role in photochemistry, even when present in the atmosphere at relatively low concentrations (1.6%). It participates in both gas and solid phase chemistry, leading to the formation of other sulfur gas products (CH3SH/SO, C2H4S/OCS, SO2/S2, and CS2) and to an increase in solid haze particle production and compositional complexity. Our study shows that we may expect thicker haze with small particle sizes (20 to 140 nm) for warm CO2-rich exoplanet atmospheres that possess H2S.Observations 1-5 and laboratory simulations 6,7 have shown that clouds and/or hazes are likely ubiquitous in the atmospheres of exoplanets. These clouds and hazes play an important role in exoplanet atmospheres and affect the spectra of planets, therefore impacting our ability to observe their atmosphere and assess their habitability. Although a variety of atmospheric gases can condense at specific temperature and pressure conditions to form clouds, haze particles may be produced photochemically over a range of temperatures, pressures, and atmospheric compositions. 6−9 Among the various atmospheric components, sulfur gases significantly influence the photochemistry and haze formation in the atmospheres of Solar System bodies, such as Earth, Venus 10,11 , Jupiter 12,13 , and its moon, Io.

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Section: Haze Production Ratesupporting

confidence: 90%

Section: Haze Production Ratementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Sulfur-driven haze formation in warm CO2-rich exoplanet atmospheres

He¹,

Hörst²,

Lewis³

et al. 2020

Nat Astron

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“…However, since all the observed planets do not have large methane concentrations, other pathways might be more important. Particularly, recent experiments at ≈ 1500 K by (Fleury et al 2019) have shown that photochemical hazes can form in a pure H2-CO gas at high temperature. Haze and condensation clouds are expected to be affected differently by the atmospheric circulation.…”

Section: Hazementioning

confidence: 99%

Atmospheric Dynamics of Hot Giant Planets and Brown Dwarfs

2020

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Groundbased and spacecraft telescopic observations, combined with an intensive modeling effort, have greatly enhanced our understanding of hot giant planets and brown dwarfs over the past ten years. Although these objects are all fluid, hydrogen worlds with stratified atmospheres overlying convective interiors, they exhibit an impressive diversity of atmospheric behavior. Hot Jupiters are strongly irradiated, and a wealth of observations constrain the day-night temperature differences, circulation, and cloudiness. The intense stellar irradiation, presumed tidal locking and modest rotation leads to a novel regime of strong day-night radiative forcing. Circulation models predict large day-night temperature differences, global-scale eddies, patchy clouds, and, in most cases, a fast eastward jet at the equator—equatorial superrotation. The warm Jupiters lie farther from their stars and are not generally tidally locked, so they may exhibit a wide range of rotation rates, obliquities, and orbital eccentricities, which, along with the weaker irradiation, leads to circulation patterns and observable signatures predicted to differ substantially from hot Jupiters. Brown dwarfs are typically isolated, rapidly rotating worlds; they radiate enormous energy fluxes into space and convect vigorously in their interiors. Their atmospheres exhibit patchiness in clouds and temperature on regional to global scales—the result of modulation by large-scale atmospheric circulation. Despite the lack of irradiation, such circulations can be driven by interaction of the interior convection with the overlying atmosphere, as well as self-organization of patchiness due to cloud-dynamical-radiative feedbacks. Finally, irradiated brown dwarfs help to bridge the gap between these classes of objects, experiencing intense external irradiation as well as vigorous interior convection. Collectively, these diverse objects span over six orders of magnitude in intrinsic heat flux and incident stellar flux, and two orders of magnitude in rotation rate—thereby placing strong constraints on how the circulation of giant planets (broadly defined) depend on these parameters. A hierarchy of modeling approaches have yielded major new insights into the dynamics governing these phenomena.

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“…Critically, exoplanet aerosol experiments have demonstrated that methane, long used in the exoplanet literature as an essential component of haze formation (e.g. Morley et al, 2015;Kawashima & Ikoma, 2018;Gao et al, 2020), is not always needed to produce substantial amounts of haze (Hörst et al, 2018;He et al, 2018b;Fleury et al, 2019;He et al, 2020bHe et al, , 2020a and that exoplanet hazes likely contain more than just hy- Figure 10. Laboratory hazes made from hydrogen-rich, water-rich, and carbon dioxide-rich atmospheres from 300 K to 600 K have a range of colors at visible wavelengths, some unlike those seen in solar system hazes (He et al, 2018a).…”

mentioning

confidence: 99%