Planet condensation

To continue with Laplace s model As the rate of rotation increased to the point where the centrifugal force at the periphery exceeded gravitation, a ring of material separated from the main mass, eventually contracting towards a point. As the process continued, more planets condensed in the outer regions, while the inner region contracted to form the snn. The satelhtes were formed by condensation from the contracting planets. Excess material between the planets turned into comets and meteors. 

Effects of condensation are also seen in the bulk compositions of the planets and their satellites. The outer planets, Uranus and Neptune, have overall densities consistent with their formation from icy and stony solids. The satellites of Uranus have typical densities of 1.3g/cm which would tend to indicate a large ice com-... 

Water and carbon play critical roles in many of the Earth s chemical and physical cycles and yet their origin on the Earth is somewhat mysterious. Carbon and water could easily form solid compounds in the outer regions of the solar nebula, and accordingly the outer planets and many of their satellites contain abundant water and carbon. The type I carbonaceous chondrites, meteorites that presumably formed in the asteroid belt between the terrestrial and outer planets, contain up to 5% (m/m) carbon and up to 20% (m/m) water of hydration. Comets may contain up to 50% water ice and 25% carbon. The terrestrial planets are comparatively depleted in carbon and water by orders of magnitude. The concentration of water for the whole Earth is less that 0.1 wt% and carbon is less than 500 ppm. Actually, it is remarkable that the Earth contains any of these compounds at all. As an example of how depleted in carbon and water the Earth could have been, consider the moon, where indigenous carbon and water are undetectable. Looking at Fig. 2-4 it can be seen that no water- or carbon-bearing solids should have condensed by equilibrium processes at the temperatures and pressures that probably were typical in the zone of fhe solar... 

The earlier assumption that Luna was a body which had been captured by the Earth can now be regarded as relatively unlikely. The same is true for the double planet hypothesis , according to which Luna and the Earth were formed at the same time from condensing primordial matter (Taylor, 1994). There are, however, still disagreements on the point in time at which the collision occurred and on the masses and the physical states of the heavenly bodies involved (Halliday and Drake, 1999). 

The volatile materials would have vaporised from the surface of the planetesimals once the temperature reached 160 K below this temperature water sticks to silicate surfaces and condenses, ultimately freezing into ice. The new gaseous material is swept away from the planetesimals by the solar wind of particles, leaving bare planetesimals too small to acquire and maintain an atmosphere. The temperature gradient and location within the solar nebula are then important to the ultimate nature and composition of the planets themselves and interplanetary debris. 

Dry air rising in the atmosphere has to expand as the pressure in the atmosphere decreases. This pV work decreases the temperature in a regular way, known as the adiabatic lapse rate, Td, which for the Earth is of order 9.8 Kkm-1. As the temperature decreases, condensable vapours begin to form and the work required for the expansion is used up in the latent heat of condensation of the vapour. In this case, the lapse rate for a condensable vapour, the saturated adiabatic lapse rate, is different. At a specific altitude the environmental lapse rate for a given parcel of air with a given humidity reaches a temperature that is the same as the saturated adiabatic lapse rate, when water condenses and clouds form Clouds in turn affect the albedo and the effective temperature of the planet. Convection of hot, wet (containing condensable vapour) air produces weather and precipitation. This initiates the water cycle in the atmosphere. Similar calculations may be performed for all gases, and cloud layers may be predicted in all atmospheres. 

The Earth s crust, mantle and core are strongly influenced by differentiation processes which could have resulted from gravitational separation ( smelting ) in an early molten phase of the planet, or from the sequence in which different chemical species condensed from the primitive solar nebula and were subsequently accreted. Seismology indicates that there is a liquid core (with a solid inner core) with radius 3500 km consisting mainly of iron (with some Ni and FeS) surrounded by a plastic (Fe, Mg silicate) mantle of thickness 2900 km. 

Langmuir, C. H., Vocke, R. D., Hanson, G. N. Hart, S. R. (1978). A general mixing equation with applications to Icelandic basalts. Earth Planet. Sci. Letters, 37, 380-92. Larimer, J. W. (1967). Chemical fractionations in meteorites - I. Condensation of the elements. Geochim. Cosmochim. Acta, 31, 1215-38. 

Wark DA (1986) Evidence for successive episodes of condensation at high temperature in a part of the solar nebula. Earth Planet Sci Lett 77 129-148... 

Planet Earth acquired an ocean early in its history, probably by 3.8 billion years before present. Most of the water is thought to have been released during the process of differentiation in which density-driven convection and cooling caused the still-molten planet to separate into layers of decreasing density, i.e., core, mantle, crust, and atmosphere. Once the crust had cooled sufficiently, gaseous water condensed to form a permanent ocean. 

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... 

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. 

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. 

Lunine, J. I. (2005) Origin of water ice in the solar system. In Meteorites and the Early Solar System II, eds. Lauretta, D. S. and McSween, H. Y., Jr. Tucson University of Arizona Press, pp. 309-319. A thoughtful review of the condensation of ices in the nebula and the delivery of ices to the terrestrial planets. 

The equilibrium-condensation model assumes that solids thermally equilibrated with the surrounding nebular gas, and any uncondensed elements were somehow flushed from the system. Planets accreted from these solids would then have compositions dictated by condensation theory. Because temperature and pressure decreased away from the Sun, the condensed solids would have varied with heliocentric distance. Figure 14.7 shows planets... 

Equilibrium condensation model for planet bulk compositions, assuming that temperature and pressure decreased outward from the Sun, as shown by the heavy curved line. Modified from Barshay and Lewis (1976). 

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