Source of Atomic Hydrogen in the Atmosphere of HD 209458b

Liang, Mao‐Chang; Parkinson, C. D.; Lee, Anthony Y. T.; Yung, Yuk L.; Seager, Sara

doi:10.1086/379314

Cited by 112 publications

(170 citation statements)

References 21 publications

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“…As for the lower boundary condition, we adopt Jovian auroral mixing ratios (Grodent et al 2001) for models with a = 0.2-1 AU, while for a < 0.2 AU we use the mixing ratio of H from Liang et al (2003). We assume the planets to be tidally synchronized if the orbital distance is between 0.047 and 0.2 AU and to be rotating asynchronously with a period of 10 hr beyond 0.2 AU.…”

Section: Methodsmentioning

confidence: 99%

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Ionization of Extrasolar Giant Planet Atmospheres

Koskinen

Cho

Achilleos

et al. 2010

ApJ

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Many extrasolar planets orbit close in and are subject to intense ionizing radiation from their host stars. Therefore, we expect them to have strong, and extended, ionospheres. Ionospheres are important because they modulate escape in the upper atmosphere and can modify circulation, as well as leave their signatures, in the lower atmosphere. In this paper, we evaluate the vertical location Z I and extent D I of the EUV ionization peak layer. We find that Z I ≈ 1-10 nbar-for a wide range of orbital distances (a = 0.047-1 AU) from the host star-and D I /H p 15, where H p is the pressure scale height. At Z I , the plasma frequency is ∼80-450 MHz, depending on a. We also study global ion transport, and its dependence on a, using a three-dimensional thermosphere-ionosphere model. On tidally synchronized planets with weak intrinsic magnetic fields, our model shows only a small, but discernible, difference in electron density from the dayside to the nightside (∼9 × 10 13 m −3 to ∼2 × 10 12 m −3 , respectively) at Z I . On asynchronous planets, the distribution is essentially uniform. These results have consequences for hydrodynamic modeling of the atmospheres of close-in extrasolar giant planets.

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Section: Methodsmentioning

confidence: 99%

“…be dissociated in reactions involving carbon and oxygen species (e.g., Liang et al 2003;Garcia Munoz 2007), but we do not consider such reactions here.…”

Section: H 2 Breakdown Regionmentioning

confidence: 99%

Ionization of Extrasolar Giant Planet Atmospheres

Koskinen

Cho

Achilleos

et al. 2010

ApJ

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“…However, contrary to our network, none of them have been validated as a whole through experiments. Line et al (2011) use the chemical network conceived for Jovian planets (Liang et al 2003(Liang et al , 2004, and reference therein), which has been updated for high temperature (Line et al 2010) and enhanced with nitrogen reactions and a small set of H 2 S reactions. Miller-Ricci Kempton et al (2012) use the chemical network of Zahnle et al (2009b), which is also originally made for Jovian planets (Zahnle et al 1995) and upgraded for high temperature atmospheres with an arbitrary selection of new reaction rates from available data (Zahnle et al 2009a).…”

Section: Kineticsmentioning

confidence: 99%

The atmospheric chemistry of the warm Neptune GJ 3470b: Influence of metallicity and temperature on the CH₄/CO ratio

Venot¹,

Agúndez²,

Selsis³

et al. 2014

A&A

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Context. Current observation techniques are able to probe the atmosphere of some giant exoplanets and get some clues about their atmospheric composition. However, the chemical compositions derived from observations are not fully understood. For instance, the CH 4 /CO abundance ratio is often inferred to be different from the value that has been predicted by chemical models. Recently, the warm Neptune GJ 3470b has been discovered, and because of its close distance from us and high transit depth, it is a very promising candidate for follow-up characterisation of its atmosphere. Aims. We study the atmospheric composition of GJ 3470b to compare to the current observations of this planet and to prepare for future ones but also to understand the chemical composition of warm (sub-)Neptunes as a typical case study. The metallicity of such atmospheres is totally uncertain and are likely to vary to values up to 100× solar. We explore the space of unknown parameters to predict the range of possible atmospheric compositions. Methods. We use a one-dimensional chemical code to compute a grid of models with various thermal profiles, metallicities, eddy diffusion coefficient profiles, and stellar UV incident fluxes. Thanks to a radiative transfer code, we then compute the corresponding emission and transmission spectra of the planet and compare them with the observational data already published. Results. Within the parameter space explored we find that methane is the major carbon-bearing species in most cases. We, however, find that for high metallicities with a sufficiently high temperature, the CH 4 /CO abundance ratio can become lower than unity, as suggested by some multiwavelength photometric observations of other warm (sub-)Neptunes, such as GJ 1214b and GJ 436b. As for the emission spectrum of GJ 3470b, brightness temperatures at infrared wavelengths may vary between 400 and 800 K depending on the thermal profile and metallicity. Conclusions. Combined with a hot temperature profile, a substantial enrichment in heavy elements by a factor of ≥100 with respect to the solar composition can shift the carbon balance in favour of carbon monoxide at the expense of methane. Nevertheless, current observations of this planet do not allow us yet to determine which model is more accurate.

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“…However, the effects of these species on the CO/CH 4 reactions has not been explored here. Conceivably, OH and H coming from the photolysis of H 2 O (Liang et al 2003) could influence the reaction rates of the Yung et al (1988) sequence.…”

Section: Eddy Diffusionmentioning

confidence: 99%

Dynamics and Disequilibrium Carbon Chemistry in Hot Jupiter Atmospheres, with Application to HD 209458b

Cooper

Showman

2006

ApJ

233

340

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Chemical equilibrium considerations suggest that, assuming solar elemental abundances, carbon on HD 209458b is sequestered primarily as carbon monoxide (CO) and methane (CH 4 ). The relative mole fractions of CO(g) and CH 4 (g) in chemical equilibrium are expected to vary greatly according to variations in local temperature and pressure. We show, however, that in the p ¼ 1Y1000 mbar range, chemical equilibrium does not hold. To explore disequilibrium effects, we couple the chemical kinetics of CO and CH 4 to a three-dimensional numerical model of HD 209458b's atmospheric circulation. These simulations show that vigorous dynamics caused by uneven heating of this tidally locked planet homogenize the CO and CH 4 concentrations at p < 1 bar, even in the presence of lateral temperature variations of $500Y1000 K. In the 1Y1000 mbar pressure range we find that over 98% of the carbon is in CO. This is true even in cool regions where CH 4 is much more stable thermodynamically. Our work shows, furthermore, that planets 300Y500 K cooler than HD 209458b can also have abundant CO in their upper layers due to disequilibrium effects. We demonstrate several interesting observational consequences of these results. Subject headingg s: atmospheric effects -methods: numerical -planetary systemsplanets and satellites: general -planets and satellites: individual (HD 09458b)

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Source of Atomic Hydrogen in the Atmosphere of HD 209458b

Cited by 112 publications

References 21 publications

Ionization of Extrasolar Giant Planet Atmospheres

Ionization of Extrasolar Giant Planet Atmospheres

The atmospheric chemistry of the warm Neptune GJ 3470b: Influence of metallicity and temperature on the CH₄/CO ratio

Dynamics and Disequilibrium Carbon Chemistry in Hot Jupiter Atmospheres, with Application to HD 209458b

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Source of Atomic Hydrogen in the Atmosphere of HD 209458b

Cited by 112 publications

References 21 publications

Ionization of Extrasolar Giant Planet Atmospheres

Ionization of Extrasolar Giant Planet Atmospheres

The atmospheric chemistry of the warm Neptune GJ 3470b: Influence of metallicity and temperature on the CH4/CO ratio

Dynamics and Disequilibrium Carbon Chemistry in Hot Jupiter Atmospheres, with Application to HD 209458b

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The atmospheric chemistry of the warm Neptune GJ 3470b: Influence of metallicity and temperature on the CH₄/CO ratio