Aging of Titan's Aerosols

Dimitrov, Vasili; Bar‐Nun, A.

doi:10.1006/icar.2001.6802

Cited by 21 publications

(35 citation statements)

References 44 publications

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“…We conclude that Titan's lower atmosphere is more photochemically active than so far assumed. In addition, experimental results presented here can be extrapolated to shorter wavelength solar radiation at higher altitudes, exposure to which should lead to condensed-phase processing of accumulations of unsaturated organic molecules as previously suggested 11,12 . Thus, tholin-like haze formation occurs by a variety of different photo-initiated processes throughout the whole atmospheric column of Titan.…”

Section: Discussionmentioning

confidence: 61%

“…7), grow through coagulation in the lower atmosphere down to 500 km (refs 8-10), and finally rain down onto the surface. It has been suggested that ultraviolet-induced chemical processing (aging and hardening) of these aerosols can occur via solid-state polymerization 11,12 . Other observations and modelling studies infer that about 60% of the total column mass production of tholin-like aerosols may occur below 300 km (ref.…”

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confidence: 99%

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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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Section: Discussionmentioning

confidence: 61%

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confidence: 99%

Photochemical activity of Titan’s low-altitude condensed haze

et al. 2013

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“…In particular, Dimitrov & Bar-Nun (1999) proposed a model of an energy-dependent agglomeration of hydrocarbon aerosol particles in Titan's atmosphere, and several of the particle properties predicted by their model have been confirmed by the DISR results (Bar-Nun et al 2008). On that basis, Dimitrov & Bar-Nun (2002, 2003 investigated the possible aging or hardening of the haze particles and proposed that there might be a region of major change in the haze properties around 570 or 620 km altitude, depending on the type of aging, either spontaneous or forced: above this level, the haze particles are fine and sticky, containing a large proportion of double-bond C=C; below this, the particles become less sticky and completely aged or hardened, with a smaller proportion of double bonds.…”

Section: Introductionmentioning

confidence: 83%

“…Previously, only a limited selection of haze spectra derived from the VIMS data around 3 μm have been presented (Kim et al 2011;Sim et al 2013). In this work, we take full advantage of the VIMS solar occultation data of Bellucci (2008), and we examine the vertical variation of the 3-μm feature to verify or confute the transition proposed by Dimitrov & Bar-Nun (2002, 2003. We then discuss an updated scenario for the aging of the haze particles, based on the soderived variations of the chemical composition of the haze.…”

Section: Introductionmentioning

confidence: 84%

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Three-micron extinction of the Titan haze in the 250–700 km altitude range: Possible evidence of a particle-aging process

Courtin¹,

Kim²,

Bar‐Nun³

2014

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Context. The chemical nature of the Titan haze is poorly understood. The investigation carried out by the Cassini-Huygens suite of instruments is bringing new insights into this question. Aims. This work aims at deriving the vertical variation of the spectral structure of the 3.3-3.4 μm absorption feature of the Titan haze from Cassini VIMS solar occultation data recorded between 250 and 700 km altitude. Methods. We computed the transmittance of Titan's atmosphere using a spherical shell model and a radiative transfer code including the influence of CH 4 , CH 3 D, and C 2 H 6 , as well as the effects of absorption and scattering by the haze particles. We derived the haze extinction from a comparison of the synthetic spectra with the VIMS solar occultation spectra. Results. We find a marked change in the relative amplitudes of the 3.33 and 3.38 μm features, which are characteristic of aromatic (double C=C chains or rings) or aliphatic (single C-C chains) structural groups, respectively. The pseudo-ratio of aromatics to aliphatics (uncorrected for the absolute band strengths) varies from 3.3 ± 1.9 at 580−700 km to 0.9 ± 0.1 at 350−450 km, and is 0.5 ± 0.1 around 250 km. The structural change from the aromatic to the aliphatic type between 580 and 480 km appears to correspond to a spontaneous aging of the particles -a transition between unannealed and hardened particles -while the further decrease of the pseudo-ratio of aromatics to aliphatics below 480 km may be related to the coating of the core particles by condensates such as heavy alkanes.

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