Production and condensation of organic gases in the atmosphere of Titan

Sagan, Carl; Thompson, W. R.

doi:10.1016/0019-1035(84)90018-6

Cited by 236 publications

(150 citation statements)

References 89 publications

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“…We only conclude based on our experiments that these other processes are not needed to explain the observed persistence and prevalence of crystalline ice in the middle and outer regions of the solar system. Considering Titan, near its surface, the energy deposition from cosmic rays is about 3.16×10 -10 erg cm -3 s -1 , 43 giving a dose of 1.68 eV molecule -1 in 4 billion years. This dose equals to only 0.5 hour irradiation in our experiments, which means most of the water ice on Titan's surface should be crystalline.…”

Section: Discussionmentioning

confidence: 99%

On the State of Water Ice on Saturn’s Moon Titan and Implications to Icy Bodies in the Outer Solar System

2009

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The crystalline state of water ice in the Solar System depends on the temperature history of the ice and the influence of energetic particles to which it has been exposed. We measured the infrared absorption spectra of amorphous and crystalline water ice in the 10-50 K and 10-140 K temperature range, respectively, and conducted a systematic experimental study to investigate the amorphization of crystalline water ice via ionizing radiation irradiation at doses of up to 160 ± 30 eV per molecule. We found that crystalline water ice can be converted only partially to amorphous ice by electron irradiation. The experiments showed that a fraction of the 1.65 µm band, which is characteristic for crystalline water ice, survived the irradiation, to a degree that strongly depends on the temperature. Quantitative kinetic fits of the temporal evolution of the 1.65 µm band clearly demonstrate that there is a balance between thermal recrystallization and irradiation-induced amorphization, with thermal recrystallizaton dominant at higher temperatures.Our experiments show the amorphization at 40K was incomplete, in contradiction to Mastrapa and Brown's conclusion (Icarus 2006, 183, 207.). At 50 K, the recrystallization due to thermal effects is strong, and most of the crystalline ice survived. Temperatures of most icy objects in the Solar System, including Jovian satellites, Saturnian satellites (including Titan), and Kuiper Belt Objects, are equal to or above 50 K; this explains why water ice detected on those objects is mostly crystalline.3

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Section: Discussionmentioning

confidence: 99%

On the State of Water Ice on Saturn’s Moon Titan and Implications to Icy Bodies in the Outer Solar System

2009

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“…The condensed phase (liquid seas of hydrocarbons, or methane trapped in porous crustal structures) remains cold enough to avoid isotopic re-equilibration among the methane and other hydrocarbon species (e.g., H+CH 3 D 4 HD+ CH 3 is too slow to be signi®cant). Also the¯ux of cosmic rays at the surface is su ciently small that cosmic-ray driven fractionation is a minor e ect (Sagan and Thompson, 1984).…”

Section: Enrichment Of Deuterium Through Methane Photochemistrymentioning

confidence: 99%

On the volatile inventory of Titan from isotopic abundances in nitrogen and methane

Lunine

Yung

Lorenz

1999

Planetary and Space Science

102

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We analyze recently published nitrogen and hydrogen isotopic data to constrain the initial volatile abundances on Saturn's giant moon Titan. The nitrogen data are interpreted in terms of a model of non-thermal escape processes that lead to enhancement in the heavier isotope. We show that these data do not, in fact, strongly constrain the abundance of nitrogen present in Titan's early atmosphere, and that a wide range of initial atmospheric masses (all larger than the present value) can yield the measured enhancement. The enrichment in deuterated methane is now much better determined than it was when Pinto et al. (1986. Nature 319, 388±390) ®rst proposed a photochemical mechanism to preferentially retain the deuterium. We develop a simple linear theory to provide a more reliable estimate of the relative dissociation rates of normal and deuterated methane. We utilize the improved data and models to compute initial methane reservoirs consistent with the observed enhancement. The result of this analysis agrees with an independent estimate for the initial methane abundance based solely on the present-day rate of photolysis and an assumption of steady state. This consistency in reservoir size is necessary but not su cient to infer that methane photolysis has proceeded steadily over the age of the solar system to produce large quantities of less volatile organics. Our analysis indicates an epoch of early atmospheric escape of nitrogen, followed by a later addition of methane by outgassing from the interior. The results also suggest that Titan's volatile inventory came in part or largely from a circum-Saturnian disk of material more reducing than the surrounding solar nebula. Many of the ambiguities inherent in the present analysis can be resolved through Cassini±Huygens data and a program of laboratory studies on isotopic and molecular exchange processes. The value of, and interest in, the Cassini±Huygens data can be greatly enhanced if such a program were undertaken prior to the prime phase of the mission. #

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“…Titan is unique in the solar system because it is the only terrestrial body besides Earth that has a substantial N 2 -dominated atmosphere, making it a possible analogue for an early, prebiotic Earth [cf. Clarke and Ferris, 1997;Sagan and Thompson, 1984;Yung et al, 1984]. Thus, understanding Titan's atmospheric evolution is key to determining how Earth's atmosphere may have transitioned into its current state [Yung and Demore, 1999].…”

Section: Introductionmentioning

confidence: 99%

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

et al. 2014

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In this study, we develop a best fit description of Titan's upper atmosphere between 500 km and 1500 km, using a one‐dimensional (1‐D) version of the three‐dimensional (3‐D) Titan Global Ionosphere‐Thermosphere Model. For this modeling, we use constraints from several lower atmospheric Cassini‐Huygens investigations and validate our simulation results against in situ Cassini Ion‐Neutral Mass Spectrometer (INMS) measurements of N2, CH4, H2, 40Ar, HCN, and the major stable isotopic ratios of 14N/15N in N2. We focus our investigation on aspects of Titan's upper atmosphere that determine the amount of atmospheric escape required to match the INMS measurements: the amount of turbulence, the inclusion of chemistry, and the effects of including a self‐consistent thermal balance. We systematically examine both hydrodynamic escape scenarios for methane and scenarios with significantly reduced atmospheric escape. Our results show that the optimum configuration of Titan's upper atmosphere is one with a methane homopause near 1000 km and atmospheric escape rates of 1.41–1.47 ×1011 CH4 m−2 s−1 and 1.08 ×1014 H2 m−2 s−1 (scaled relative to the surface). We also demonstrate that simulations consistent with hydrodynamic escape of methane systematically produce inferior fits to the multiple validation points presented here.

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Production and condensation of organic gases in the atmosphere of Titan

Cited by 236 publications

References 89 publications

On the State of Water Ice on Saturn’s Moon Titan and Implications to Icy Bodies in the Outer Solar System

On the State of Water Ice on Saturn’s Moon Titan and Implications to Icy Bodies in the Outer Solar System

On the volatile inventory of Titan from isotopic abundances in nitrogen and methane

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

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