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Astrochemistry is the area of study where astronomy and chemistry overlap. In essence it is the study of the abundance and reactions of chemical elements and molecules in the universe. The formation, atomic and chemical composition, evolution and fate of molecular gas clouds is of special interest, because it is from these clouds that solar systems form. The most important tool in this area of study is spectroscopy.
Spectroscopy is the use of telescopes to measure the absorption and emission of light from molecules and atoms in various environments. The abundance of elements, chemical composition, and temperatures can be inferred from astronomical observations when compared to laboratory measurements. This is possible because ions, atoms, and molecules have characteristic ways that they absorb and emit certain wavelengths (colors) of light, often not visible to the human eye. On the other hand, these measurements have limitations, with various types of radiation (radio, infrared, visible, ultraviolet etc.) able to detect only certain types of species, depending on the chemical properties of the molecules.
Radio astronomy is the most powerful technique for detection of individual molecules. It has resulted in the detection of over a hundred interstellar species including:radicals, ions, and carbon-based compounds(alcohols, acids, ketones). One of the most abundant interstellar molecules is carbon monoxide(CO). It is such a common interstellar molecule that it is used to map out molecular regions.
Infrared astronomy has also been used to assess the composition of solid materials in the interstellar medium, including silicates, carbon-rich solids, and ices, because, unlike visible light, the IR radiation can pass through the microscopic interstellar particles, but there are absorptions at certain wavelengths that are characteristic of the composition of the grains. These observations have determined that in dense clouds thin ice layers coat the microscopic particles, permitting some low-temperature chemistry to occur. Since hydrogen is by far the most abundant molecule in the universe, the initial chemistry of these ices is determined by the chemistry of the hydrogen. If the hydrogen is atomic, then the H atoms react with available O, C and N atoms; but, if the hydrogen is molecular and thus not reactive, this permits the heavier atoms to react or remain bonded together. These mixed-molecular ices are exposed to ultraviolet radiation and cosmic rays which results in complex radiation-driven chemistry.
Further research is needed to completely assess the implications of astrochemistry. Scientists are just beginning to find a great variety of chemical species.
If you’d like more info on Astrochemistry, check out NASA Ames Research Center’s Astrophysics & Astrochemistry Laboratory, and here’s a link to Wikipedia.
We’ve also recorded an entire episode of Astronomy Cast all about Molecules in Space. Listen here, Episode 116: Molecules in Space.