Observation of Ices in Space

Observation of Ices in Space 9.1.2.1. Interstellar Molecular Clouds 

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 H20 ice is clear, its abundance being one order of magnitude greater than that of all other molecules. The molecules CO and C02 are those next most abundant, following H20. Small amounts of reduced molecules, hydrocarbons and NH3 are also observed. 

By comparing the observed spectra with spectra measured in the laboratoiy, one can determine the crystallinity of icy grains [3]. For Elias 16 (a molecular cloud), the observed feature around 3 pm fits the spectrum of amorphous ice at 

For the BN object (a protostar), the spectrum is optimized for a mixture of ices at representative temperatures of 23 K (amorphous), 77 K (amorphous), and 150K (crystalline ice). This shows that the BN have various temperatures ranging from circumstellar to molecular cloud temperatures, depending on the distance from the central protostar. 

The recent approach of large comets such as lP/Halley, C/1996 B2 Hyakutake, and C/1995 01 Hale-Bopp to the Earth provided a good opportunity to investigate the detailed composition of cometary ices by various methods such as mass spectrometry, infrared spectroscopy, and radio emission. The composition of interstellar ices is compared with that of the cometaiy ices in Table 9.3. It is striking that cometaiy and interstellar ices have quite comparable relative molecular abundances. 

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