THERMOCHEMICAL AND PHOTOCHEMICAL KINETICS IN COOLER HYDROGEN-DOMINATED EXTRASOLAR PLANETS: A METHANE-POOR GJ436b?

Line, Michael R.; Vasisht, Gautam; Chen, Pin; Angerhausen, Daniel; Yung, Yuk L.

doi:10.1088/0004-637x/738/1/32

Cited by 125 publications

(234 citation statements)

References 67 publications

(143 reference statements)

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“…Furthermore, in cooler planets such as hot Neptunes orbiting M dwarfs (e.g., GJ 436b) the temperature contrast between day and nightsides decreases because the cooling rate scales with the cube of temperature (e.g., A73, page 18 of 21 Lewis et al 2010), and therefore the composition is expected to be even more homogeneous with longitude than in warmer planets such as HD 209458b and HD 189733b. However, unlike hot Jupiters, hot Neptunes may have an atmospheric metallicity much higher than solar (Line et al 2011;Moses et al 2013;Agúndez et al 2014;Venot et al 2014), which makes it interesting to investigate the extent of the spatial variation of molecular abundances in their atmospheres.…”

Section: Discussionmentioning

confidence: 99%

“…The circulation pattern in these planets is characterized by an equatorial superrotating eastward jet. On the other hand, the chemical composition of hot Jupiters has been investigated by one-dimensional models, which currently account for thermochemical kinetics, vertical mixing, and photochemistry (Zahnle et al 2009;Line et al 2010Line et al , 2011Moses et al 2011Moses et al , 2013Kopparapu et al 2012;Venot et al 2012Venot et al , 2014Agúndez et al 2014). These models have revealed the existence of three different chemical regimes in the vertical direction.…”

Section: Introductionmentioning

confidence: 99%

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Pseudo 2D chemical model of hot-Jupiter atmospheres: application to HD 209458b and HD 189733b

Agúndez

Parmentier

Venot

et al. 2014

A&A

139

265

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The high temperature contrast between the day and night sides of hot-Jupiter atmospheres may result in strong variations of the chemical composition with longitude if the atmosphere were at chemical equilibrium. On the other hand, the vigorous dynamics predicted in these atmospheres, with a strong equatorial jet, would tend to supress such longitudinal variations. To address this subject we have developed a pseudo two-dimensional model of a planetary atmosphere, which takes into account thermochemical kinetics, photochemistry, vertical mixing, and horizontal transport, the latter being modeled as a uniform zonal wind. We have applied the model to the atmospheres of the hot Jupiters HD 209458b and HD 189733b. The adopted eddy diffusion coefficients were calculated by following the behavior of passive tracers in three-dimensional general circulation models, which results in much lower eddy values than in previous estimates. We find that the distribution of molecules with altitude and longitude in the atmospheres of these two hot Jupiters is complex because of the interplay of the various physical and chemical processes at work. Much of the distribution of molecules is driven by the strong zonal wind and the limited extent of vertical transport, resulting in an important homogenization of the chemical composition with longitude. The homogenization is more marked in planets lacking a thermal inversion such as HD 189733b than in planets with a strong stratosphere such as HD 209458b. In general, molecular abundances are quenched horizontally to values typical of the hottest dayside regions, and thus the composition in the cooler nightside regions is highly contaminated by that of warmer dayside regions. As a consequence, the abundance of methane remains low, even below the predictions of previous one-dimensional models, which probably is in conflict with the high CH 4 content inferred from observations of the dayside of HD 209458b. Another consequence of the important longitudinal homogenization of the abundances is that the variability of the chemical composition has little effect on the way the emission spectrum is modified with phase and on the changes in the transmission spectrum from the transit ingress to the egress. These variations in the spectra are mainly due to changes in the temperature, rather than in the composition, between the different sides of the planet.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Pseudo 2D chemical model of hot-Jupiter atmospheres: application to HD 209458b and HD 189733b

Agúndez

Parmentier

Venot

et al. 2014

A&A

139

265

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“…Figure 9 compares the flux received at the top of the atmosphere of a GJ 436b-like planet with the different stars. We used the model described in Venot et al (2012) and the same temperature profile as Line et al (2011) calculated by Lewis et al (2010). Although this is not a realistic assumption, we used the same temperature for all three host stars.…”

Section: Application To Exoplanetsmentioning

confidence: 99%

“…The atmosphere of transiting hot Jupiters and hot Neptunes can be studied by spectroscopy at the primary transit (Tinetti et al 2007b,a;Swain et al 2008;Beaulieu et al 2010Beaulieu et al , 2011Tinetti et al 2010) and at the secondary eclipse (Swain et al 2009a,b;Stevenson et al 2010Stevenson et al , 2012. Photochemistry has an important influence on the atmospheric composition of these exoplanets, from the top of the atmosphere down to 100 mbar (Moses et al 2011;Line et al 2011;Venot et al 2012). For these exoplanets and within this large pressure range, the temperature can vary roughly from 400 to 2500 K. To model correctly the photochemistry of these planets, we need to use absorption cross sections consistent with these temperatures for all the species whose photolysis plays an important role in either the formation/destruction of molecules or in the penetration of the UV flux into the atmosphere.…”

Section: Introductionmentioning

confidence: 99%

High-temperature measurements of VUV-absorption cross sections of CO₂and their application to exoplanets

Venot

Fray

Bénilan

et al. 2013

A&A

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Context. Ultraviolet (UV) absorption cross sections are an essential ingredient of photochemical atmosphere models. Exoplanet searches have unveiled a large population of short-period objects with hot atmospheres, very different from what we find in our solar system. Transiting exoplanets whose atmospheres can now be studied by transit spectroscopy receive extremely strong UV fluxes and have typical temperatures ranging from 400 to 2500 K. At these temperatures, UV photolysis cross section data are severely lacking. Aims. Our goal is to provide high-temperature absorption cross sections and their temperature dependency for important atmospheric compounds. This study is dedicated to CO 2 , which is observed and photodissociated in exoplanet atmospheres. We also investigate the influence of these new data on the photochemistry of some exoplanets. Methods. We performed these measurements with synchrotron radiation as a tunable VUV light source for the 115-200 nm range at 300, 410, 480, and 550 K. In the 195-230 nm range, we used a deuterium lamp and a 1.5 m Jobin-Yvon spectrometer and we worked at seven temperatures between 465 and 800 K. We implemented the measured cross section into a 1D photochemical model. Results. For λ > 170 nm, the wavelength dependence of ln(σ CO 2 (λ, T ) × 1 Qv(T ) ) can be parametrized with a linear law. Thus, we can interpolate σ CO 2 (λ, T ) at any temperature between 300 and 800 K. Within the studied range of temperature, the CO 2 cross section can vary by more than two orders of magnitude. This, in particular, makes the absorption of CO 2 significant up to wavelengths as high as 230 nm, while it is negligible above 200 nm at 300 K. Conclusions. The absorption cross section of CO 2 is very sensitive to temperature, especially above 160 nm. The model predicts that accounting for this temperature dependency of CO 2 cross section can affect the computed abundances of NH 3 , CO 2 , and CO by one order of magnitude in the atmospheres of hot Jupiter and hot Neptune. This effect will be more important in hot CO 2 -dominated atmospheres.

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“…The analysis of GJ 436b cannot be considered conclusive, though, given the activity of the star (Knutson et al 2011) and the lack of spectroscopic data: only photometric data, often recorded at different times, are available for this target. The presence of methane is predicted by photochemical models (Moses et al 2011;Line et al 2011), but would need further spectroscopic confirmation on a larger sample of targets. The HST/NICMOS transit observations of the planet HD189733b (Swain et al 2008) led to the identification of H 2 O and CH 4 in the atmosphere of that planet (see also Waldmann et al 2013 and.…”

Section: Primary Transit Observationsmentioning

confidence: 94%

Spectroscopy of planetary atmospheres in our Galaxy

Tinetti

Encrenaz

Coustenis

2013

Astron Astrophys Rev

128

111

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About 20 years after the discovery of the first extrasolar planet, the number of planets known has grown by three orders of magnitude, and continues to increase at neck breaking pace. For most of these planets we have little information, except for the fact that they exist and possess an address in our Galaxy. For about one third of them, we know how much they weigh, their size and their orbital parameters. For less than 20, we start to have some clues about their atmospheric temperature and composition. How do we make progress from here?We are still far from the completion of a hypothetical Hertzsprung-Russell diagram for planets comparable to what we have for stars, and today we do not even know whether such classification will ever be possible or even meaningful for planetary objects. But one thing is clear: planetary parameters such as mass, radius and temperature alone do not explain the diversity revealed by current observations. The chemical composition of these planets is needed to trace back their formation history and evolution, as happened for the planets in our Solar System. As in situ measurements are and will remain off-limits for exoplanets, to study their chemical composition we will have to rely on remote sensing spectroscopic observations of their gaseous envelopes.

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THERMOCHEMICAL AND PHOTOCHEMICAL KINETICS IN COOLER HYDROGEN-DOMINATED EXTRASOLAR PLANETS: A METHANE-POOR GJ436b?

Cited by 125 publications

References 67 publications

Pseudo 2D chemical model of hot-Jupiter atmospheres: application to HD 209458b and HD 189733b

Pseudo 2D chemical model of hot-Jupiter atmospheres: application to HD 209458b and HD 189733b

High-temperature measurements of VUV-absorption cross sections of CO₂and their application to exoplanets

Spectroscopy of planetary atmospheres in our Galaxy

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THERMOCHEMICAL AND PHOTOCHEMICAL KINETICS IN COOLER HYDROGEN-DOMINATED EXTRASOLAR PLANETS: A METHANE-POOR GJ436b?

Cited by 125 publications

References 67 publications

Pseudo 2D chemical model of hot-Jupiter atmospheres: application to HD 209458b and HD 189733b

Pseudo 2D chemical model of hot-Jupiter atmospheres: application to HD 209458b and HD 189733b

High-temperature measurements of VUV-absorption cross sections of CO2and their application to exoplanets

Spectroscopy of planetary atmospheres in our Galaxy

Contact Info

Product

Resources

About

High-temperature measurements of VUV-absorption cross sections of CO₂and their application to exoplanets