Titan’s aerosol and stratospheric ice opacities between 18 and 500μm: Vertical and spectral characteristics from Cassini CIRS

Anderson, C. M.; Samuelson, R. E.

doi:10.1016/j.icarus.2011.01.024

Cited by 112 publications

(128 citation statements)

References 60 publications

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“…On the theoretical side, we expect that the largest errors come from the determination of the coefficients in the spherical harmonic expansion of the dipole moment surface in Eq. (2). Inaccuracy in the higher spherical-harmonic coefficients affects only the far wings of the spectra, as can be seen from Fig.…”

Section: B Anisotropic Interaction Potentialmentioning

confidence: 80%

“…14 The absorption coefficient is defined by Lambert's law, which predicts exponential decay of the intensity, I(z) ∝ exp(−αz), with the path length, z. In first order perturbation theory, the absorption coefficient at frequency ω is given by α(ω, T) = 2π 2 3 c n 2 ω…”

Section: A Summarymentioning

confidence: 99%

“…Therefore, accurate knowledge of the collision-induced spectra is required for remote-sensing studies. 2 Collisions with abundant N 2 molecules also lead to broadening of strong absorption lines, 3 such as the water continua in the Earth's atmosphere. 4 The far infrared absorption of N 2 pairs also contributes to surface warming, 5 and this mechanism may be essential in explaining the presence of liquid water on early Mars.…”

Section: Introductionmentioning

confidence: 99%

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Quantum mechanical calculation of the collision-induced absorption spectra of N2–N2 with anisotropic interactions

Karman

Miliordos

Hunt

et al. 2015

The Journal of Chemical Physics

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We present quantum mechanical calculations of the collision-induced absorption spectra of nitrogen molecules, using ab initio dipole moment and potential energy surfaces. Collision-induced spectra are first calculated using the isotropic interaction approximation. Then, we improve upon these results by considering the full anisotropic interaction potential. We also develop the computationally less expensive coupled-states approximation for calculating collision-induced spectra and validate this approximation by comparing the results to numerically exact close-coupling calculations for low energies. Angular localization of the scattering wave functions due to anisotropic interactions affects the line strength at low energies by two orders of magnitude. The effect of anisotropy decreases at higher energy, which validates the isotropic interaction approximation as a high-temperature approximation for calculating collision-induced spectra. Agreement with experimental data is reasonable in the isotropic interaction approximation, and improves when the full anisotropic potential is considered. Calculated absorption coefficients are tabulated for application in atmospheric modeling. C 2015 AIP Publishing LLC. [http://dx

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Section: B Anisotropic Interaction Potentialmentioning

confidence: 80%

Section: A Summarymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Quantum mechanical calculation of the collision-induced absorption spectra of N2–N2 with anisotropic interactions

Karman

Miliordos

Hunt

et al. 2015

The Journal of Chemical Physics

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“…Titan's unusual dense and oxygen-depleted atmosphere has a wide variety of linear unsaturated polyynes-nitrogen-containing polycyanoacetylenes 19 , such as C 4 N 2 as well as polyacetylenes 20 and aromatic molecules 21 -that undergo photopolymerization forming complex tholin-like molecules, whose structure is still under intense investigation 22 . Recent laboratory studies showed that when these tholins come into contact with oxygen-bearing molecules such as water (surface/subsurface ice on Titan), result in the formation of complex prebiotic molecules such as amino acids 5 and nucleobases 23,24 .…”

mentioning

confidence: 99%

Photochemical activity of Titan’s low-altitude condensed haze

et al. 2013

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Titan, the largest moon of Saturn and similar to Earth in many aspects, has unique orangeyellow colour that comes from its atmospheric haze, whose formation and dynamics are far from well understood. Present models assume that Titan's tholin-like haze formation occurs high in atmosphere through gas-phase chemical reactions initiated by high-energy solar radiation. Here we address an important question: Is the lower atmosphere of Titan photochemically active or inert? We demonstrate that indeed tholin-like haze formation could occur on condensed aerosols throughout the atmospheric column of Titan. Detected in Titan's atmosphere, dicyanoacetylene (C 4 N 2 ) is used in our laboratory simulations as a model system for other larger unsaturated condensing compounds. We show that C 4 N 2 ices undergo condensed-phase photopolymerization (tholin formation) at wavelengths as long as 355 nm pertinent to solar radiation reaching a large portion of Titan's atmosphere, almost close to the surface.

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“…Evidence of clouds in Titan's atmosphere has clearly been seen, and three types of clouds are categorized: convective methane clouds (Brown et al 2002;Griffith et al 1998Griffith et al , 2000Griffith et al , 2005Griffith et al , 2009Roe et al 2005;Rodriguez et al 2009Rodriguez et al , 2011Turtle et al 2009Turtle et al , 2011Schaller et al 2006), stratiform ethane clouds (Roe et al 2002;Griffith et al 2006;Tokano et al 2006;Schaller et al 2006Schaller et al , 2009Le Mouélic et al 2012), and highaltitude cirrus containing HCN and HC 3 N (Samuelson et al 2007;Anderson et al 2010;Anderson & Samuelson 2011). Although the presence of clouds has been established, we do not sufficiently understand their formation mechanisms, particle size distribution, and chemical composition.…”

Section: Introductionmentioning

confidence: 95%

Methane-Nitrogen Binary Nucleation: A New Microphysical Mechanism for Cloud Formation in Titan's Atmosphere

Tsai

Liang

Chen

2012

ApJ

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It is known that clouds are present in the troposphere of Titan; however, their formation mechanism, particle size, and chemical composition remain poorly understood. In this study, a two-component (CH 4 and N 2 ) bin-microphysics model is developed and applied to simulate cloud formation in the troposphere of Titan. A new process, binary nucleation of particles from CH 4 and N 2 gases, is considered. The model is validated and calibrated by recent laboratory experiments that synthesize particle formation in Titan-like environments. Our model simulations show that cloud layers can be formed at about 20 km with a particle size ranging from one to several hundred μm and number concentration 10 −2 to over 100 cm −3 depending on the strength of the vertical updraft. The particles are formed by binary nucleation and grow via the condensation of both CH 4 and N 2 gases, with their N 2 mole fraction varying from <10% in the nucleation stage to >30% in the condensation growth stage. The locally occurring CH 4 -N 2 binary nucleation mechanism is strong and could potentially be more important than the falling condensation nuclei mechanism assumed in many current models.

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Titan’s aerosol and stratospheric ice opacities between 18 and 500μm: Vertical and spectral characteristics from Cassini CIRS

Cited by 112 publications

References 60 publications

Quantum mechanical calculation of the collision-induced absorption spectra of N2–N2 with anisotropic interactions

Quantum mechanical calculation of the collision-induced absorption spectra of N2–N2 with anisotropic interactions

Photochemical activity of Titan’s low-altitude condensed haze

Methane-Nitrogen Binary Nucleation: A New Microphysical Mechanism for Cloud Formation in Titan's Atmosphere

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