Chemistry of the Solar Nebula

Fegley, B.

doi:10.1007/978-94-011-1936-8_4

Cited by 32 publications

(25 citation statements)

References 178 publications

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“…This means that parent bodies of carbonaceous chondrites were accreted from a predominantly anhydrous material that was mixed with water ice, which subsequently melted. Although formation of hydrous minerals in a high-pressure Jovian subnebula might not have been as strongly inhibited as in the solar nebula [Fegley, 1993] …”

Section: Mass Balance Models For Oceanic Chemistrymentioning

confidence: 99%

Composition and stability of salts on the surface of Europa and their oceanic origin

2001

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Abstract. We present theoretical models of the composition, the relative abundances, and the stability of hydrated salts on the surface and in the icy shell of Jupiter's satellite Europa and discuss whether those salts have an oceanic origin. The evaluations were done with thermodynamic calculations of (1) salt dehydration equilibria at the conditions of the surface of Europa and its icy shell, (2) chemical equilibria involving solids and water vapor in the Na-K-Mg-Ca-S-C1-H20 system at surface temperatures and variable partial pressures of water vapor, and (3) changes in aquatic chemistry and sequences of salt precipitation from freezing oceanic water, using cosmochemical, mass balance, and physical-chemical constraints on the elemental and ionic composition of the ocean. Mass balance calculations of total or partial extraction of elements into an ocean from a carbonaceous chonddhte type mantle show that magnesium and sulfate rather than chloride and sodium could be the most abundant solutes in the ocean. Freezing oceanic water of this composition leads to brines that differ in composition from the original water and to deposition of ice and highly hydrated sulfates of Mg, Na, and Ca as well as alkali chlorides. After freezing is complete, highly hydrated salts remain stable in ice-bearing surface matedhals and throughout the icy shell. For hypothetical surface salt lag deposits, formed through sublimation/sputtedhng of ice and dehydration of salts, we predict hydration stratification with depth, approaching the highest hydration states in ice-beadhng matedhals in the lowest parts of the deposits. We discuss the effects of fast disequilibrium freezing and variable dehydration rates of salts on the predicted mineral assemblages at the surface. All of our models, which are independent of observations, predict the predominance of Mg and Na sulfates in surface salts, in agreement with spectroscopic models for the nonicy surface matedhal in the near infrared spectral region. IntroductionGalileo spacecraft reflectance spectroscopy in the near-infrared spectral region tentatively indicates the presence of hydrated saks in a non-H20 ice component on the surface of Jupiter's moon Europa [McCord et al., 1998a[McCord et al., , 1998b[McCord et al., , 1999. It was shown that magnesium and sodium sulfates (MgSO4.7H20, epsomite; MgSO4.Na2SO4.4H20, bloedite; Na2SO4.10H20, mirabilite), sodium carbonate (Na2CO3.10H20, natron), and mixtures of these salts provide good fits for the near-infrared spectra for the nonicy material Here we undertake evaluations of this type from a theoretical basis. In this paper we present internally consistent geochemical and thermodynamic models that describe leaching of aqueous components from a silicate mantle, aquatic chemistry of the ocean, freezing of oceanic water during upwelling in fractures in the icy crust and on the surface, and dehydration of salts on the surface of Europa. The results are compared with observational models for the composition and distribution of the nonicy surface mater...

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Section: Mass Balance Models For Oceanic Chemistrymentioning

confidence: 99%

Composition and stability of salts on the surface of Europa and their oceanic origin

2001

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“…Models of the volatile components released by comets require that some fraction ofthese materials were processed in higher temperature-pressure environments than is possible in the outer solar nebula (Prinn and Fegley, 1989;Fegley, 1993Fegley, , 1999. It was previously hypothesized that giant gaseous protoplanetary subnebulae could have provided such environments, yet there is little observational evidence that suggests that these subnebulae even exist in modem protostellar systems.…”

Section: Catalytic Chemistry and Cometary Agesmentioning

confidence: 99%

Condensation processes in astrophysical environments: The composition and structure of cometary grains

Nuth

Rietmeijer

Hill

2002

Meteorit & Planetary Scien

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Abstract-We review the results ofour recent experimental studies ofastrophysical dust analogs. We discuss the condensation of amorphous silicates from mixed metal vapors, including evidence that such condensates form with metastable eutectic compositions. We consider the spectral evolution of amorphous magnesium silicate condensates as a function oftime and temperature. Magnesium silicate smokes anneal readily at temperatures of about 1000-1100 K. In contrast we find that iron silicates require much higher temperatures (--1300 K) to bring about similar changes on the same timescale (days to months). We first apply these results to infrared space observatory observations ofcrystalline magnesium silicate grains around high-mass-outflow asymptotic giant branch stars in order to demonstrate their general utility in a rather simple environment. Finally, we apply these experimental results to infrared observations ofcomets and proto stars in order to derive some interesting conclusions regarding large-scale nebular dynamics, the natural production of organic molecules in protostellar nebulae, and the use of crystalline magnesium silicates as a relative indicator of a comet's formation age.

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“…Large quantities of complex prebiotic materials could greatly simplify chemical evolution in planetary environments starting from a rich organic broth and leading to the simplest forms of living organisms. Many mechanisms may contribute to the total organic content in protostellar nebulae, ranging from organics formed via ion-molecule and atom-molecule reactions in the cold dark clouds from which such nebulae collapse (Nuth et al 2006), to similar ion-molecule and atom-molecule reactions in the dark regions of the nebula far from the protostar (Ciesla & Charnley 2006), to gas-phase reactions in subnebulae around growing giant planets (Fegley 1993) and in the nebulae themselves. It is unclear that any of these mechanisms could produce enough material to account for the relatively large quantities of organics found in the most primitive meteorites (Pizzarello et al 2006).…”

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A Self-Perpetuating Catalyst for the Production of Complex Organic Molecules in Protostellar Nebulae

Nuth

Johnson

Manning

2008

ApJ

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When hydrogen, nitrogen, and CO are exposed to amorphous iron silicate surfaces at temperatures between 500 and 900 K a carbonaceous coating forms via Fischer-Tropsch-type reactions. Under normal circumstances such a coating would impede or stop further reaction. However, we find that this coating is a better catalyst than the amorphous iron silicates that initiate these reactions. Formation of a self-perpetuating catalytic coating on grain surfaces could explain the rich deposits of macromolecular carbon found in primitive meteorites and would imply that protostellar nebulae should be rich in organic material.

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Chemistry of the Solar Nebula

Cited by 32 publications

References 178 publications

Composition and stability of salts on the surface of Europa and their oceanic origin

Composition and stability of salts on the surface of Europa and their oceanic origin

Condensation processes in astrophysical environments: The composition and structure of cometary grains

A Self-Perpetuating Catalyst for the Production of Complex Organic Molecules in Protostellar Nebulae

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