Clathrate hydrates as a sink of noble gases in Titan's atmosphere

Thomas, C.; Mousis, O.; Ballenegger, V.; Picaud, Sylvain

doi:10.1051/0004-6361:20078072

Cited by 46 publications

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“…61 The Kr and Xe deficiencies could simply be explained by the presence of clathrates on the surface of Titan that would have efficiently incorporated these noble gases. 7,52 On the other hand, in order to interpret the Ar deficiency in the atmosphere of Titan, it has been proposed that the satellite was formed from icy planetesimals initially produced in the solar nebula and that were partially devolatilized at a temperature not exceeding ∼ 50 K during their migration within Saturn's subnebula. 13 In this case, because Ar is poorly trapped in clathrates formed above ∼ 50 K in the nebula, only tiny amounts of this compound would have been incorporated in the building blocks of the forming Titan, in agreement with the observations.…”

Section: The Argon Deficiency In Titanmentioning

confidence: 99%

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Volatile inventories in clathrate hydrates formed in the primordial nebula

et al. 2010

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Examination of ambient thermodynamic conditions suggest that clathrate hydrates could exist in the martian permafrost, on the surface and in the interior of Titan, as well as in other icy satellites. Clathrate hydrates probably formed in a significant fraction of planetesimals in the solar system. Thus, these crystalline solids may have been accreted in comets, in the forming giant planets and in their surrounding satellite systems. In this work, we use a statistical thermodynamic model to investigate the composition of clathrate hydrates that may have formed in the primordial nebula. In our approach, we consider the formation sequence of the different ices occurring during the cooling of the nebula, a reasonable idealization of the process by which volatiles are trapped in planetesimals. We then determine the fractional occupancies of guests in each clathrate hydrate formed at given temperature. The major ingredient of our model is the description of the guest-clathrate hydrate interaction by a spherically averaged Kihara potential with a nominal set of parameters, most of which being fitted on experimental equilibrium data. Our model allows us to find that Kr, Ar and N 2 can be efficiently encaged in clathrate hydrates formed at temperatures higher than ∼ 48.5 K in the primitive nebula, instead of forming pure condensates below 30 K. However, we find at the same time that the determination of the relative abundances of guest species incorporated in these clathrate hydrates strongly depends on the choice of the parameters of the Kihara potential and also on the adopted size of cages. Indeed, testing different potential parameters, we have noted that even minor dispersions between the different existing sets can lead to non-negligible variations in the determination of the volatiles trapped in clathrate hydrates formed in the primordial nebula. However, these variations are not found to be strong enough to reverse the relative abundances between the different volatiles in the clathrate hydrates themselves. On the other hand, if contraction or expansion of the cages due to temperature variations are imposed in our model, the Ar and Kr mole fractions can be modified up to several orders of magnitude in clathrate hydrates. Moreover, mole fractions of other molecules such as N 2 or CO are also subject to strong changes with the variation of the size of the cages. Our results may affect the predictions of the composition of the planetesimals formed in the outer solar system. In particular, the volatile abundances calculated in the giant planets atmospheres should be altered because these quantities are proportional to the mass of accreted and vaporized icy planetesimals. For similar reasons, the estimates of the volatile budgets accreted by icy satellites and comets may also be altered by our calculations. For instance, under some conditions, our calculations predict that the abundance of argon in the atmosphere of Titan should be higher than the value measured by Huygens. Moreover, the Ar abundance in comets...

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Section: The Argon Deficiency In Titanmentioning

confidence: 99%

“…[4][5][6][7][8] Moreover, it has been suggested that the activity observed in some cometary nuclei results from the dissociation of these crystalline structures. 9 Generally speaking, clathrates probably participated in the formation of planetesimals in the solar system.…”

Section: Introductionmentioning

confidence: 99%

Volatile inventories in clathrate hydrates formed in the primordial nebula

et al. 2010

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“…Thomas et al (2007) have proposed the formation of clathrate hydrates on Titan's surface as a sink for krypton and xenon, while Osegovic & Max (2005) have calculated that compound clathrates could explain the absence of xenon and presumably krypton as well. The arguments presented above show that the special conditions required for clathrate formation are not required to explain the T. Owen and H. B. Niemann upper limits on these two gases given the detection threshold of the GCMS.…”

Section: (D ) Noble Gasesmentioning

confidence: 99%

The origin of Titan's atmosphere: some recent advances

Owen

Niemann

2008

Phil. Trans. R. Soc. A.

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It is possible to make a consistent story for the origin of Titan's atmosphere starting with the birth of Titan in the Saturn subnebula. If we use comet nuclei as a model, Titan's nitrogen and methane could have easily been delivered by the ice that makes up approximately 50 per cent of its mass. If Titan's atmospheric hydrogen is derived from that ice, it is possible that Titan and comet nuclei are in fact made of the same protosolar ice. The noble gas abundances are consistent with relative abundances found in the atmospheres of Mars and Earth, the Sun, and the meteorites.

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“…The authors calculated the composition of clathrates on the surface of Titan using the program CSMHYD (developed by Sloan (1998)) and showed that such crystalline ice structures may act as a sink for Xe. The facts that the code used by Osegovic & Max (2005) is not suitable below about 140 K for gas mixtures of interest, and that the authors did not explicitly calculate the trapping efficiencies of Ar and Kr in clathrates on the surface of Titan led Thomas et al (2007) to reconsider their results. In particular, Thomas et al (2007) performed more accurate calculations of the trapping of noble gases in clathrates using a statistical thermodynamic model based on experimental data and on the original work of van der Waals & Platteeuw (1959).…”

Section: Introductionmentioning

confidence: 99%

“…The facts that the code used by Osegovic & Max (2005) is not suitable below about 140 K for gas mixtures of interest, and that the authors did not explicitly calculate the trapping efficiencies of Ar and Kr in clathrates on the surface of Titan led Thomas et al (2007) to reconsider their results. In particular, Thomas et al (2007) performed more accurate calculations of the trapping of noble gases in clathrates using a statistical thermodynamic model based on experimental data and on the original work of van der Waals & Platteeuw (1959). On this basis, Thomas et al (2007) showed that Xe and Kr could have been progressively absorbed in clathrates located at the surface of Titan during its thermal history, in contrast with Ar, which is poorly trapped in these crystalline structures.…”

Section: Introductionmentioning

confidence: 99%

A theoretical investigation into the trapping of noble gases by clathrates on Titan

Thomas

Picaud

Mousis

et al. 2008

Planetary and Space Science

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In this paper, we use a statistical thermodynamic approach to quantify the efficiency with which clathrates on the surface of Titan trap noble gases. We consider different values of the Ar, Kr, Xe, CH 4 , C 2 H 6 and N 2 abundances in the gas phase that may be representative of Titan's early atmosphere. We discuss the effect of the various parameters that are chosen to represent the interactions between the guest species and the ice cage in our calculations. We also discuss the results of varying the size of the clathrate cages. We show that the trapping efficiency of clathrates is high enough to significantly decrease the atmospheric concentrations of Xe and, to a lesser extent, of Kr, irrespective of the initial gas phase composition, provided that these clathrates are abundant enough on the surface of Titan. In contrast, we find that Ar is poorly trapped in clathrates and, as a consequence, that the atmospheric abundance of argon should remain almost constant. We conclude that the mechanism of trapping noble gases via clathration can explain the deficiency in primordial Xe and Kr observed in Titan's atmosphere by Huygens, but that this mechanism is not sufficient to explain the deficiency in Ar.

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Clathrate hydrates as a sink of noble gases in Titan's atmosphere

Cited by 46 publications

References 15 publications

Volatile inventories in clathrate hydrates formed in the primordial nebula

Volatile inventories in clathrate hydrates formed in the primordial nebula

The origin of Titan's atmosphere: some recent advances

A theoretical investigation into the trapping of noble gases by clathrates on Titan

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