13C and 15N fractionation of CH4/N2 mixtures during photochemical aerosol formation: Relevance to Titan

Sebree, Joshua A.; Stern, J. C.; Mandt, K.; Domagal-Goldman, Shawn; Trainer, M. G.

doi:10.1016/j.icarus.2015.04.016

Cited by 34 publications

(14 citation statements)

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“…Nitrogen incorporation was recently observed in the aerosols generated by far-UV photolysis of CH 4 /CO 2 /N 2 gas mixtures (Trainer, 2013) and in CH 4 /N 2 mixtures (Sebree et al , 2015). These results bring to light a significant but still unknown mechanism regarding the activation of nitrogen and its inclusion in oxygenated organics, thus providing a new and quantifiable source for these two elements into the early Earth aerosols.…”

Section: Discussionmentioning

confidence: 93%

The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth

et al. 2016

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Recognizing whether a planet can support life is a primary goal of future exoplanet spectral characterization missions, but past research on habitability assessment has largely ignored the vastly different conditions that have existed in our planet's long habitable history. This study presents simulations of a habitable yet dramatically different phase of Earth's history, when the atmosphere contained a Titan-like, organic-rich haze. Prior work has claimed a haze-rich Archean Earth (3.8–2.5 billion years ago) would be frozen due to the haze's cooling effects. However, no previous studies have self-consistently taken into account climate, photochemistry, and fractal hazes. Here, we demonstrate using coupled climate-photochemical-microphysical simulations that hazes can cool the planet's surface by about 20 K, but habitable conditions with liquid surface water could be maintained with a relatively thick haze layer (τ ∼ 5 at 200 nm) even with the fainter young Sun. We find that optically thicker hazes are self-limiting due to their self-shielding properties, preventing catastrophic cooling of the planet. Hazes may even enhance planetary habitability through UV shielding, reducing surface UV flux by about 97% compared to a haze-free planet and potentially allowing survival of land-based organisms 2.7–2.6 billion years ago. The broad UV absorption signature produced by this haze may be visible across interstellar distances, allowing characterization of similar hazy exoplanets. The haze in Archean Earth's atmosphere was strongly dependent on biologically produced methane, and we propose that hydrocarbon haze may be a novel type of spectral biosignature on planets with substantial levels of CO2. Hazy Archean Earth is the most alien world for which we have geochemical constraints on environmental conditions, providing a useful analogue for similar habitable, anoxic exoplanets. Key Words: Haze—Archean Earth—Exoplanets—Spectra—Biosignatures—Planetary habitability. Astrobiology 16, 873–899.

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Section: Discussionmentioning

confidence: 93%

The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth

et al. 2016

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“…In addition, with N2 in the initial gas mixture, several new gas products are nitrogen-containing species. The new gas products are indicative of the composition of the solid haze particles; the formation of nitrogen-containing molecules in the gas phase suggests that nitrogen may also be incorporated into solid particles (Imanaka & Smith 2010, He & Smith 2013, 2014Carrasco et al 2015;Sebree et al 2016;Hicks et al 2016;Gautier et al 2017;Hörst et al 2018b;Berry et al 2019aBerry et al , 2019bUgelow et al 2020). Gas molecules will be easier to detect than complex haze compositions with remote sensing techniques.…”

Section: Mass Spectra Of Gas Phase Productsmentioning

confidence: 99%

“…As shown in Figure 4, the 1000× metallicity case contains higher concentration of CO (14% versus 3.5%), and two extra gases (CO2 and N2). CO2 and extra CO can provide more carbon sources for producing organic hazes, while nitrogen from N2 could be also incorporated into the solid haze particles (Imanaka & Smith 2010, He & Smith 2013, 2014Carrasco et al 2015;Sebree et al 2016;Hicks et al 2016;Gautier et al 2017;Hörst et al 2018b). There is less H2 (43% versus 76%) in the 1000× metallicity case, but the fraction is still more than sufficient to provide a reducing environment in which (He et al 2020, Reed et al 2020 show that small amount of H2S could enhance haze production rate significantly.…”

Section: Haze Production Ratementioning

confidence: 99%

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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“…The behaviour of a photochemical system depends on the quantity of photons per reagent but also on the optical depth of the gas mixture in the cell. The optical depth of the gas mixture influences the photochemical processes 25,45,81 . The processes in a photon-dominated environment will not be the same as in a reactant-dominated environment.…”

Section: Methodsmentioning

confidence: 99%

“…Secondary photolysis processes of the photoproducts may occur and lead to the formation of unwanted species and overpolymerization compared to the initial aerosol formation processes in Titan's atmosphere 36,43,44 . Experiments can then last up to hundreds of hours to form solid particles and generate enough material for ex situ analysis [29][30][31][45][46][47] .…”

mentioning

confidence: 99%

On an EUV Atmospheric Simulation Chamber to Study the Photochemical Processes of Titan’s Atmosphere

Bourgalais

Carrasco

Vettier

et al. 2020

Sci Rep

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the in situ exploration of titan's atmosphere requires the development of laboratory experiments to understand the molecular growth pathways initiated by photochemistry in the upper layers of the atmosphere. Key species and dominant reaction pathways are used to feed chemical network models that reproduce the chemical and physical processes of this complex environment. energetic UV photons initiate highly efficient chemistry by forming reactive species in the ionospheres of the satellite. We present here a laboratory experiment based on a new closed and removable photoreactor coupled here to an extreme Ultraviolet (eUV) irradiation beam produced by the high-order harmonic generation of a femtosecond laser. this type of eUV stable source allow long-term irradiation experiments in which a plethora of individual reactions can take place. in order to demonstrate the validity of our approach, we irradiated for 7 hours at 89.2 nm, a gas mixture based on N 2 /cH 4 (5%). Using only one wavelength, products of the reaction reveal an efficient photochemistry with the formation of large hydrocarbons but especially organic compounds rich in nitrogen similar to titan. Among these nitrogen compounds, new species had never before been identified in the mass spectra obtained in situ in titan's atmosphere. their production in this experiment, on the opposite, corroborates previous experimental measurements in the literature on the chemical composition of aerosol analogues produced in the laboratory. Diazo-compounds such as dimethyldiazene (c 2 H 6 n 2), have been observed and are consistent with the large nitrogen incorporation observed by the aerosols collector pyrolysis instrument of the Huygens probe. this work represents an important step forward in the use of a closed cell chamber irradiated by the innovative eUV source for the generation of photochemical analogues of titan aerosols. this approach allows to better constrain and understand the growth pathways of nitrogen incorporation into organic aerosols in titan's atmosphere.

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13C and 15N fractionation of CH4/N2 mixtures during photochemical aerosol formation: Relevance to Titan

Cited by 34 publications

References 34 publications

The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth

The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth

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

On an EUV Atmospheric Simulation Chamber to Study the Photochemical Processes of Titan’s Atmosphere

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