Dust Chemistry and Astrobiology
Interstellar gas phase chemistry is effective in producing a range of simple molecules, including many organic molecules. Earlier chapters in this book have described how greater chemical complexity can be achieved through the chemical processing of mixed ices on the surfaces of dust grains in dense, dark regions of interstellar space. The range of these more complex molecules—the so-called COMs—appears to be fairly insensitive to the precise method of chemical processing. These COMs are of great interest to astrobiology, but are simpler than the molecules involved in biological processes. An environment in which molecules even more complex than COMs may possibly be formed is described: it is cavity chemistry. When ice-coated dust grains aggregate together in clumps, and eventually in planetesimals, a large volume fraction remains unoccupied. The products of ice processing are retained within these cavities and subjected to the repeated processing and additions of metals from the underlying grains. The nature of the chemistry in these cavities is in principle similar to the famous Miller–Urey experiment in which a variety of amino acids was formed. Finally, it is a characteristic of biological molecules that they are chiral. The possible role of cavity chemistry in inducing chirality in molecules that are trapped in the cavities is explored.