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Interstellar ices molecular clouds

Two types of models have been proposed that use this general picture as the basis for understanding volatile depletions in chondrites. Yin (2005) proposed that the volatile element depletions in the chondrites reflect the extent to which these elements were sited in refractory dust in the interstellar medium. Observations show that in the warm interstellar medium, the most refractory elements are almost entirely in the dust, while volatile elements are almost entirely in the gas phase. Moderately volatile elements are partitioned between the two phases. The pattern for the dust is similar to that observed in bulk chondrites. In the Sun s parent molecular cloud, the volatile and moderately volatile elements condensed onto the dust grains in ices. Within the solar system, the ices evaporated putting the volatile elements back into the gas phase, which was separated from the dust. Thus, in Yin s model, the chondrites inherited their compositions from the interstellar medium. A slightly different model proposes that the fractionated compositions were produced in the solar nebula by... [Pg.206]

Ice mantles are important constituents of interstellar grains in molecular clouds, and icy bodies dominate the outer reaches of the solar system. The region of the solar system where ices were stable increased with time as the solar system formed, as accretion rates of materials to the disk waned and the disk cooled. The giant planets and their satellites formed, in part, from these ices, and probably also from the nebular gas itself. [Pg.355]

The chemical composition of ices in space is inferred theoretically on the basis of condensation theory, which predicts tlie composition of solids condensed from gas of Uie cosmic abundance of elements. In Table 9.2, chemical compositions of ices and corresponding equilibrium condensation temperatures are shown in protosolar nebula [1] and interstellar molecular clouds [2],... [Pg.109]

Yamamoto et al. [2] made a condensation calculation to estimate tlie chemical composition of the ice in molecular clouds and cometaiy nuclei. They assumed tlie interstellar molecular composition for tlie abundance of gas. Inter-... [Pg.109]

Observation of Ices in Space 9.1.2.1. Interstellar Molecular Clouds... [Pg.242]

Infrared spectroscopy enables us to obtain information on the chemical composition and structure of icy grains in interstellar molecular clouds [3], Table 9.3 summarizes the abundance of molecules identified [4]. Among these species, the predominance of H2O ice is clear, its abundance being one order of magnitude greater than that of all odier molecules. The molecules CO and CO2 are those next most abundant, following H2O. Small amounts of reduced molecules, hydrocarbons and NH3 are also observed. [Pg.242]

The chemistry of dense, dark molecular clouds prior to planet formation is the topic of this paper. Dr. Ziurys has discussed the inventory and measurement of gas phase interstellar molecules associated with dense molecular clouds in the chapter, "Identifying Molecules in Space" 8). Here, the focus is on the chemistry in and on the ices and the interaction of these ices with species in the gas. Since these ices represent the largest repository of interstellar molecules in dense clouds, they tie up a large fraction of the chemical inventory in molecular... [Pg.84]

The picture of mixed molecular interstellar ice described up to this point is supported by direct spectroscopic evidence (e.g. Figures 2, 3). The identities, relative amounts and absolute abundances of the ice species listed in Table I are sound (see references 6 and 7 and references therein for detailed discussions). However, this is not the entire story. Indeed, from a chemist s perspective, this is only the beginning of the story. As mentioned above, throughout the cloud s lifetime, processes such as accretion of gas phase species, simultaneous reactions on the surfaces involving atoms, ions, and radicals, as well as energetic processing within the body of the ice by ultraviolet photons and cosmic rays all combine to determine the ice mantle composition (5-7). Theoreticians are... [Pg.91]

Over the past thirty years tremendous strides have been made in our understanding of the complex chemistry in dense, dark, interstellar molecular clouds. This has come about because of fundamental advances in observational infrared astronomy and laboratory astrophysics. Thirty years ago the composition of interstellar dust was largely guessed at the concept of ices in... [Pg.104]

The formation of stars occurs through the gravitational collapse of individual galactic molecular cloud cores within dense clouds. As cold interstellar gas and ice-mantled dust grains collapsed onto the protosolar nebula. [Pg.255]


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See also in sourсe #XX -- [ Pg.85 , Pg.86 , Pg.87 , Pg.91 ]




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Clouds, interstellar molecular

Ice clouds

Interstellar

Interstellar ice

Molecular cloud

Molecular ice

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