ATMOSPHERIC SULFUR PHOTOCHEMISTRY ON HOT JUPITERS

By K. Zahnle, M. Marley, R. Freedman, K. Lodders, Jon Fortney. 2009

220 citations recorded by the source corpus.

We develop a new one-dimensional photochemical kinetics code to address stratospheric chemistry and stratospheric heating in hot Jupiters. Here we address optically active S-containing species and CO2 at 1200 ⩽ T ⩽ 2000 K. HS (mercapto) and S2 are highly reactive species that are generated photochemically and thermochemically from H2S with peak abundances between 1 and 10 mbar. S2 absorbs UV between 240 and 340 nm and is optically thick for metallicities [S/H]>0 at T ⩾ 1200 K. HS is probably more important than S2, as it is generally more abundant than S2 under hot Jupiter conditions and it absorbs at somewhat redder wavelengths. We use molecular theory to compute an HS absorption spectrum from sparse available data and find that HS should absorb strongly between 300 and 460 nm, with absorption at the longer wavelengths being temperature sensitive. When the two absorbers are combined, radiative heating (per kg of gas) peaks at 100 μbars, with a total stratospheric heating of ∼8 × 104 W m−2 for a jovian planet orbiting a solar-twin at 0.032 AU. Total heating is insensitive to metallicity. The CO2 mixing ratio is a well behaved quadratic function of metallicity, ranging from 1.6 × 10−8 to 1.6 × 10−4 for −0.3 < [M/H] < 1.7. CO2 is insensitive to insolation, vertical mixing, temperature (1200 < T < 2000), and gravity. The photochemical calculations confirm that CO2 should prove a useful probe of planetary metallicity.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/645a1d6941e702f1eb4345753ea0fa88fd0fea5b

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. N. Madhusudhan
2. Jon Fortney
3. A. Showman
4. D. Sing
5. D. Deming
6. M. Marley
7. H. Knutson
8. J. D'esert

In Instrumentation

1. Jon Fortney
2. N. Madhusudhan
3. A. Showman
4. D. Sing
5. H. Knutson
6. D. Deming
7. M. Line
8. J. D'esert

Citations in the corpus

• VULCAN: An Open-source, Validated Chemical Kinetics Python Code for Exoplanetary Atmospheres (2016, background): “When there is more than one rate coefficient available, they are selected by the following criteria (Zahnle et al. 2009): 1. validation within a better temperature range; 2. date of the publication; 3. review versus experimental versus theoretical publications (in that order).”
• THE STATISTICS OF ALBEDO AND HEAT RECIRCULATION ON HOT EXOPLANETS (2009, background): “The presence or lack of a stratospheric temperature inversion (Hubeny et al. 2003; Fortney et al. 2006; Burrows et al. 2007, 2008; Zahnle et al. 2009) on the day-sides of exoplanets has been invoked to explain a purported bi-modality in recirculation efficiency on hot Jupiters (Fortney et al. 2008).”
• TRANSMISSION SPECTRA OF THREE-DIMENSIONAL HOT JUPITER MODEL ATMOSPHERES (2009, background): “Alternatively, the obscuring material could potentially be something other than silicates—perhaps a methanederived soot (Zahnle et al. 2009a).”
• A CORRELATION BETWEEN STELLAR ACTIVITY AND HOT JUPITER EMISSION SPECTRA (2010, methodology): “We suggest that this would be best addressed by comprehensive photochemistry models such as those described in Zahnle et al. (2009, 2010) and Line, Liang, & Yung (2010).”
• NO THERMAL INVERSION AND A SOLAR WATER ABUNDANCE FOR THE HOT JUPITER HD 209458B FROM HST/WFC3 SPECTROSCOPY (2016, background): “…due to the possible presence of a strong gas phase optical absorbers (Hubeny et al. 2003; Burrows et al. 2008 ), one example being TiO and VO, which can persist at high temperatures (T>2000 K at 1 bar, Fortney et al. 2006, Fortney et al. 2008 ), or poly-sulfur aerosols (Zahnle et al. 2009).”
• DISEQUILIBRIUM CARBON, OXYGEN, AND NITROGEN CHEMISTRY IN THE ATMOSPHERES OF HD 189733b AND HD 209458b (2011, background): “Although the ultimate reasons for these differences are still under investigation (see also Spiegel et al. 2009; Zahnle et al. 2009; Knutson et al. 2010; Youdin & Mitchell 2010; Fressin et al. 2010; Machalek et al. 2008, 2010; Madhusudhan & Seager 2010a), exoplanets with thermal inversions appear…”
• Hubble Space Telescope transmission spectroscopy of the exoplanet HD 189733b: high‐altitude atmospheric haze in the optical and near‐ultraviolet with STIS (2011, background): “The larger radii at near-UV wavelengths (blueward of ∼4000 Å) could also be attributed to other absorbing features, such as a Balmer jump associated with the escaping atmosphere (Ballester, Sing & Herbert 2007) or sulfur compounds generated photochemically (Zahnle et al. 2009).”
• The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations (2012, background): “Photochemistry may also play a role in producing condensates, for instance sulphur or carbon compounds, that could affect the spectral signatures of the planetary atmosphere (e.g. Zahnle et al. 2009b).”
• Transits and Occultations (2010, background): “f this absorber in hot Jupiter atmospheres has been a topic of debate. Gaseous titanium oxide and vanadium oxide are candidates (Hubeny et al. 2003), as are photochemically-produced sulfur compounds (Zahnle et al. 2009). Meanwhile observers are searching for correlations between the presence or abse”
• SPECTROSCOPIC EVIDENCE FOR A TEMPERATURE INVERSION IN THE DAYSIDE ATMOSPHERE OF HOT JUPITER WASP-33b (2015, background): “Recent theories have postulated several additional atmospheric processes that could play a role in the formation of inversions, such as the production of photochemical sulfur-based hazes (Zahnle et al. 2009) or the inhibition of oxide formation due to a super-solar C/O ratio (Madhusudhan 2012).”
• A chemical model for the atmosphere of hot Jupiters (2012, background): “For the other molecules, such as H2, H and CO2, at the thermodynamic equilibrium, there is a steep variation in composition (smoothed by vertical mixing) corresponding to the strong temperature gradient of the upper atmosphere.”
• An HST optical-to-near-IR transmission spectrum of the hot Jupiter WASP-19b: detection of atmospheric water and likely absence of TiO (2013, methodology): “Spectroscopic observations blueward of 4000 Å can also detect Rayleigh-like signatures and potential features from sulphurcontaining molecules, which can cause millibar-level inversions (e.g. Zahnle et al. 2009).”
• A TEMPERATURE AND ABUNDANCE RETRIEVAL METHOD FOR EXOPLANET ATMOSPHERES (2009, background): “A mixing ratio of 7 × 10−4 is seemingly high from a theoretical standpoint; photochemistry which is thought to be the primary source of CO2 in hot Jupiters allows mixing ratios of CO2 up to∼ 10−6, assuming solar metallicities (Liang et al. 2003, Zahnle et al. 2009).”
• CHARACTERIZING TRANSITING EXOPLANET ATMOSPHERES WITH JWST (2015, background): “Disequilibrium Chemistry Disequilibrium processes are likely to play a role in sculpting the molecular abundances in exoplanet atmospheres (Liang et al. 2003; Zahnle et al. 2009; Line et al. 2010; Moses et al. 2011; Line et al. 2011; Venot et al. 2012; Agúndez et al. 2014; Hu et al. 2013).”
• Exoplanet Atmospheres: Physical Processes (2010, background): “For a hot atmosphere with CO as the primary carbon reservoir, CO2 could be reasonably abundant ~10-6, based on thermochemistry (Lodders & Fegley 2002) or photochemistry (Liang et al. 2003), but higher values require a high planet metallicity (Zahnle et al. 2009).”
• PHOTOCHEMISTRY IN TERRESTRIAL EXOPLANET ATMOSPHERES. I. PHOTOCHEMISTRY MODEL AND BENCHMARK CASES (2012, background): “Zahnle et al. (2009b) studied sulfur photochemistry in hot Jupiters’ atmospheres, and suggested that H2S photolysis becomes important at altitudes above the ∼100 Pa pressure level.”
• Transit spectrophotometry of the exoplanet HD189733b. I. Searching for water but finding haze with HST NICMOS (2009, background): “This planet also exhibits a stratospheric temperature inversion (Burrows et al. 2007; Knutson et al. 2008) thought to be caused by a strong optical absorber such as TiO (Désert et al. 2008; Hubeny et al. 2003; Fortney et al. 2008) and/or HS and S2 (Zahnle et al. 2009).”
• Transmission spectral properties of clouds for hot Jupiter exoplanets (2014, background): “The presence of non-equilibrium photochemical species with absorption in the blue gives their atmosphere a characteristic red colour (Zahnle et al. 2009).”
• C/O RATIO AS A DIMENSION FOR CHARACTERIZING EXOPLANETARY ATMOSPHERES (2012, background): “…non-equilibrium chemistry in the form of vertical eddy mixing and photochemistry can cause significant changes in the molecular mixing ratios, and hence, affect their spectral signatures (Zahnle et al. 2009; Line et al. 2010; Madhusudhan & Seager 2011; Moses et al. 2011; Vischer & Moses 2011).”