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- McKay, C. P., et al.
(författare)
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Possible sources for methane and C 2-C 5 organics in the plume of Enceladus
- 2012
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 71:1, s. 73-79
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Tidskriftsartikel (refereegranskat)abstract
- We consider six possible sources of CH 4 and other lowmass (C 2-C 5) organics in the plume of Enceladus: three of these sources represent initial endowments of organics: cometary organics, Titan-like tholin, and the Fisher-Tropsch type reactions in the gases from which Enceladus formed. The other three sources represent processes inside Enceladus: water-rock reactions, microbiology, and thermogenesis. We report on new laboratory results for C 2 hydrocarbons released by thermogenesis of laboratory tholin and the Fisher-Tropsch type synthesis. Thermal processing of Titan-like tholin produced ratios of CH 4/C 2H 4 and CH 4/C 2H 6 of about two for temperatures up to 450 °C and about six for a temperature of 650°C. The low pressure (∼1 atm) Fisher-Tropsch type experiments produced CH 4/C 2H 4 of ∼1.5, similar to previous results. C 2H 2 was not produced by either process. Tests of gas production by four strains of methanogens confirmed the absence of any detectable production of non-methane hydrocarbons. Cometary endowment, the Fisher-Tropsch type synthesis, and Titan-like tholin incorporation could be primary inputs of organics and subsequent thermal processing of any of these all are possible sources of low mass organics in the plume. Biological production and water-rock reactions are an alternative source of CH 4. Aqueous reactions with CO and H 2 can produce C 2-C 5 organics even at the low pressures of the interior of Enceladus. If there is a confirmed detection of CO and C 2H 2 in the plume of Enceladus, this provides an important constraint on sources, as we have identified no process, other than the initial volatile component of cometary organics, which can supply these gases. Precise determination of the relative concentrations of C 1-C 5 hydrocarbons may provide additional constraints on sources, but a detailed isotopic analysis of C and H in these organics and a search for amino acids constitute the next important steps in resolving the sources of the organics in Enceladus' plume.
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