Constraints on the Formation of Comets from D/H Ratios Measured in H2O and HCN

Mousis, O.; Gautier, D.; Bockelée‐Morvan, Dominique; Robert, François; Dubrulle, Bérengère; Drouart, A.

doi:10.1006/icar.2000.6499

Cited by 129 publications

(129 citation statements)

References 43 publications

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“…The (D/H) HCN ratios deduced from single-dish observations are summarized in Table 1. By comparison, a range of (0.4-7.0) × 10 −2 for the DCN/HCN ratio was determined in the interstellar medium (ISM) (Roberts et al 2002;Jørgensen et al 2004). The low DCN/HCN value in comets compared to the ISM can suggest some reprocessing in the Solar Nebula that occurred before the incorporation of these molecules into comets (Mousis et al 2000), as it will be discussed in depth in Sect. 4.2.…”

Section: Hcnmentioning

confidence: 99%

“…Ion-molecule reactions in the outer solar nebula could also act to lower the interstellar fractionation (Aikawa and Herbst 1999). Alternatively, the low D-enrichment in H 2 O might result from the mixing of D-rich water vapor originating from the pre-solar cloud or outer cold disk, and material reprocessed in the inner hot solar nebula (Hersant et al 2001;Mousis et al 2000;Kavelaars et al 2011). Indeed, at high temperatures (>500 K), water molecules quickly exchange their deuterium with the main hydrogen reservoir H 2 , so that the deuterium enrichment in water can not exceed the protosolar value of 0.21 ± 0.04 × 10 −4 by more than a factor of 3 (Geiss and Gloeckler 1998) in high-T conditions.…”

Section: Deuteration In the Solar Nebulamentioning

confidence: 99%

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Cometary Isotopic Measurements

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Section: Hcnmentioning

confidence: 99%

Section: Deuteration In the Solar Nebulamentioning

confidence: 99%

Cometary Isotopic Measurements

et al. 2015

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“…Thus, clathrates may have been accreted in comets, in the forming giant planets and in their surrounding satellite systems. 4,[12][13][14][17][18][19][20][21][22][23][24] During the twentieth century, many theoretical and experimental studies allowed This approach, used today in the industry and in science, has saved substantial experimental efforts for the determination of i) the equilibrium pressure of a clathrate formed from various mixtures and ii) the mole fraction of the different species trapped in the clathrate from a given fluid phase.…”

Section: Introductionmentioning

confidence: 99%

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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“…Balsiger et al (1995) and Eberhardt et al (1995) Simulations of the D/H gradient using upper limits for the ice D/H from the analysis of meteorite samples, managed to verify these observations (e.g. Drouart et al 1999;Mousis et al 2000;Horner et al 2007 andKavelaars et al 2011). Therefore, models appear to be compatible with the assumption that OCCs formed in the vicinity of the gas giants.…”

Section: Water and D/hmentioning

confidence: 74%

Constraints from Comets on the Formation and Volatile Acquisition of the Planets and Satellites

et al. 2015

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Comets play a dual role in understanding the formation and evolution of the solar system. First, the composition of comets provides information about the origin of the giant planets and their moons because comets formed early and their composition is not expected to have evolved significantly since formation. They, therefore serve as a record of conditions during the early stages of solar system formation. Once comets had formed, their orbits were perturbed allowing them to travel into the inner solar system and impact the planets. In this way they contributed to the volatile inventory of planetary atmospheres. We review here how knowledge of comet composition up to the time of the Rosetta mission has contributed to understanding the formation processes of the giant planets, their moons and small icy bodies in the solar system. We also discuss how comets contributed to the volatile inventories of the giant and terrestrial planets.

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Constraints on the Formation of Comets from D/H Ratios Measured in H2O and HCN

Cited by 129 publications

References 43 publications

Cometary Isotopic Measurements

Cometary Isotopic Measurements

Volatile inventories in clathrate hydrates formed in the primordial nebula

Constraints from Comets on the Formation and Volatile Acquisition of the Planets and Satellites

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