Solar System condensation

A We also developed laser-desorption laser-ionization mass spectrometry for the analysis of adsorbates on surfaces, such as interplanetary dust particles and meteoritic samples. We use one laser to rapidly heat the sample and evaporate molecules from the surface. A second laser intercepts the rising plume of molecules and ionizes those that absorb that color of light. We then weigh the ions using a mass spectrometer. We have analyzed graphite particles extracted from meteorites and found polycyclic aromatic molecules (PAHs). The PAHs have to isotope ratios that match closely the graphite grains, which are believed to be the remnants of the star dust from which our solar system condensed some 4.5 billion years ago. These are the first interstellar molecules observed directly in the laboratory. 

These predictions, based on the composition of early rocks, are supported by a second line of evidence, which provides a clue to the origin of this early atmosphere. This is the rarity of inert unreactive gases, particularly neon, in the Earth s atmosphere today. Neon is the seventh most abundant element in the Universe. It was abundant in the clouds of dust and gas from which the Earth and the other planets of the Solar System condensed. As an inert gas, neon is even more unreactive than nitrogen. If any of the Earth s original atmosphere had survived the meteorite bombardment, it should have contained about the same amount of neon as nitrogen. In fact, the ratio of neon to nitrogen is 1 to 60000. If there ever had been a Jupiter-like atmosphere on Earth, then it must have been swept away during that first ferocious period of meteorite bombardment. 

It is generally believed that the solar system condensed out of an interstellar cloud of gas and dust, referred to as the primordial solar nebula, about 4.6 billion years ago. The atmospheres of the Earth and the other terrestrial planets, Venus and Mars, are thought to have formed as a result of the release of trapped volatile compounds from the planet itself. The early atmosphere of the Earth is believed to have been a mixture of carbon dioxide (C02), nitrogen (N2), and water vapor (H20), with trace amounts of hydrogen (H2), a mixture similar to that emitted by present-day volcanoes. 

The Laplace equation is named for Pierre Simon, Marquis de Laplace, 1749-1827, a great French mathematician, physicist, and astronomer who also proposed that the solar system condensed from a rotating gas cloud. 

Fig. 2-4 The sequence of condensation of solids from a solar composition gas at a nebular pressure of 10 Pa (ca. 10 atm). (Modified with permission from J. A. Wood, "The Solar System," p. 162, Copyright C 1979, Prentice-Hall, Englewood Cliffs, NJ.)...

As evidenced by their low abundances, carbon compounds, water, and other volatiles such as nitrogen compounds were probably not significantly abundant constituents of the bulk of the solids that formed near the Earth. Many of the carriers of these volatiles condensed in cooler, more distant regions and were then scattered into the region where the Earth was forming. Eragments of comets and asteroids formed in the outer solar system still fall to Earth at a rate of 1 x 10 kg/yr and early in the... 

For desorption the vapor desorbed from the silica gel has to be condensed. For this reason a low temperature heat sink is required. The hydraulics of the plant provides two heat sinks a 10 m3 rain water cistern and the thermal solar plant. With these heat sinks two desorption modes could be carried out a desorption with simultaneous condensation of the vapor an a second mode in which the desorption and condensation were not done simultaneously. If desorption and condensation of the vapour occur at the same time, then the condensation heat is rejected via the rain water cistern. The condensation heat can also be removed by the solar plant when the desorption and condensation operation are discontinuous. In this case the solar plant heats up the adsorber during daytime but no condensation is done. The condensation take place through the solar system during the night given correspondingly low outside temperatures. 

When the elements are ejected from the stars where they were produced, they are in the gas phase. Subsequently, they combine in various chemical compounds and most condense as solids. The nature of those compounds and their behavior in the various environments encountered on their way to becoming part of the solar system can, in principle, be determined from the basic chemical properties of the elements. Evaporation and condensation are also important in the solar system and have played a defining role in determining the properties of planets, moons, asteroids, and the meteorites derived from them, comets, dust... 

Lodders, K. (2003) Solar system abundances and condensation temperatures of the elements. Astrophysical Journal, 591, 1220-1247. A comprehensive discussion of the solar system abundances of the elements from the perspective of a cosmochemist. 

In recent years, a new source of information about stellar nucleosynthesis and the history of the elements between their ejection from stars and their incorporation into the solar system has become available. This source is the tiny dust grains that condensed from gas ejected from stars at the end of their lives and that survived unaltered to be incorporated into solar system materials. These presolar grains (Fig. 5.1) originated before the solar system formed and were part of the raw materials for the Sun, the planets, and other solar-system objects. They survived the collapse of the Sun s parent molecular cloud and the formation of the accretion disk and were incorporated essentially unchanged into the parent bodies of the chondritic meteorites. They are found in the fine-grained matrix of the least metamorphosed chondrites and in interplanetary dust particles (IDPs), materials that were not processed by high-temperature events in the solar system. 

Because of the isotopic variability and the high cosmic abundance of oxygen, oxygen isotopes are very useful for meteorite classification. Below the condensation temperature of silicates and above the condensation temperature of ices, approximately 25% of the oxygen in the solar nebula is predicted to have occurred in condensed solids, with the remainder in gaseous molecules. Chondrites provide samples of the condensed oxygen in the early solar system. 

Vapor-solid and vapor-liquid transformations (condensation of a gas, or its reverse, evaporation) can fractionate elements and sometimes isotopes. Each element condenses over a very limited temperature range, so one would expect the composition of the condensed phase and vapor phase to change as a function of the ambient temperature. Many of the chemical fractionations that took place in the early solar system are due, in one way or another, to this phenomenon. It is convenient to quantify volatility by use of the 50% condensation temperature, that is, the temperature by which 50% of the mass of a particular element has condensed from a gas of solar composition. Table 7.1 lists the 50% condensation temperatures for the solid elements in a gas of solar composition at a pressure of... 

Applicability of condensation calculations to the early solar system... 

In summary, equilibrium condensation represents one end member of a continuum of gas-solid interactions that took place in the early solar system. Some samples appear to have formed under conditions that closely match those of equilibrium condensation. But the volatility-based fractionations that are widely observed in solar system materials are due to much more complicated processes that involve evaporation (the opposite of condensation) or mixing of materials produced under different conditions, as well as a variety of processes in which kinetic effects played an important role. 

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... 

Davis, A. M. and Richter, F. M. (2004) Condensation and evaporation of solar system materials. In Treatise on Geochemistry, Vol. 1 Meteorites, Comets and Planets, ed. Davis, A. M. Oxford Elsevier, pp. 407-430. A good recent discussion of the processes of condensation and evaporation and associated isotopic effects and their applications to solar system materials. 

Ebel, D. S. (2006) Condensation of rocky material in astrophysical environments. In Meteorites and the Early Solar System, II, eds. Lauretta, D. S. and McSween, H. Y., Jr. Tucson University of Arizona Press, Tucson, pp. 253-277. A good summary of the modem condensation calculations and modeling of solar system processes. 

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