Ice in Space

The cosmic abundance of elements forms a basis for considering the chemical composition of ice in space. The cosmic abundance of major elements is summarized in Table 9.1. The most abundant elements, H and He, are very volatile, and exist as gas in the tenuous environment in space. Elements heavier than H and He can form solids. The elements C, N, and O combine with H to form ices at temperatures lower than about 100K, and Si, Mg, and Fe combine with O to form silicates, metals, and their oxides. Note that the elements that form ices are much more abundant than the elements that form silicates and metals. 

The chemical composition of ices in space is inferred theoretically on the basis of condensation theory, which predicts the composition of solids condensed from gas of the 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]. 

In the protosolar nebula, H20 ice condenses at temperatures lower than 150K. Upon further lowering of the temperature, part of the H20 ice transforms into NH3 hydrate and CH4 clathrate hydrate. These are the compositions of ice predicted by the equilibrium condensation theory. It should be pointed out, however, that the equilibrium might not actually be realized at low temperatures. Thus, the ice composition predicted by the equilibrium condensation theory may not be the actual composition, but should be regarded as a model composition. 

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

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Observation of Ices in Space 9.1.2.1. Interstellar Molecular Clouds... 

In 1781 de la Place published the description of a much improved calorimeter. A picture of it can be found in the writings of Lavoisier [4] and is shown in Fig. 4.27. The outer cavity, a, and the lid, F, are filled with ice to insulate the interior of the calorimeter from the surroundings. Inside this first layer of ice, in space b, a second... 

With most single cells so far examined, the survivals obtained with nonequilibrium freezing procedures and vitrification are no better than those obtainable with equilibrium freezing procedures. But vitrification procedures may be necessary for the successful preservation of tissues and organs, which appear not to be able to tolerate the formation of ice in capillaries and other spaces between the cells. 

Perhaps the oldest form of energy storage is the harvesting of natural ice or snow from lakes, rivers and mountains for food preservation, cold drinks and space cooling. The following extract from 350 years ago illustrates the popularity of ice in Persia ... 

It will be recalled that Sivashinsky and Tanny also favored the idea of supercooled water whose structure is influenced by being in pores as opposed to the idea of freezing water. While the NMR experiments of Sivashinsky and Tanny were performed on the Na+ form, Tc at 250 K was 1.7 x 10 s, which is in the midrange of those obtained by MacMillan et al. for different water contents. It is difficult to imagine water as forming ice in the usual bulk sense in these confined spaces having high surface/volume. 

Fig. 484b—the cost of firing one kilogramme of porcelain may be taken as two francs—or one shilling and eight-pence while the cost of a cubic foot of space in the furnace will bo one franc ono centime—about ten-pe,ice. In Vienna, for every firing about seven klafters of wood are used, equal to sixteen and a half stacks, each of one hundred cubic feet, Hessian j in Berlin ten stocks, about seven hundred cubic feet, same measurement. 

The combined volume of all the billions of open rooms" in the hexagonal ice crystals of a piece of ice is equal to the volume of the part of the ice that extends above water when ice floats. When the ice melts, the open spaces are exaedy filled in by the amount of ice that extends above the water level. This is why the water level doesn t rise when ice in a glass of ice water melts—the melting ice caves in and exactly fills the open spaces. 

The requirements that must be met to gain the ability to tolerate freezing include the following (1) The formation of true ice is restricted to the extracellular spaces. (2) The formation of ice in the extracellular fluids is not accompanied by extreme dehydration of the cells. (3) Rates of ice crystal formation and the sizes of ice crystals that are generated in the extracellular fluids are held at nonlethal values. (4) Any solid-state water that forms within cells is vitrified water, not true ice. To meet these requirements, freeze-tolerant organisms employ a variety of mechanisms to control the sites, rates, and sizes of ice crystal formation. 

Schutte WA. Production of organic molecules in interstellar ices. Adv Space Res 2002 3 1409-17. 

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