Organics on the Rocks: A Cosmic Origin for the Seeds of Life

Interstellar gas phase chemistry is effective in producing a range of simple molecules, including many organic molecules. Such a chemical complexity can be achieved through the processing of mixed ices on the surfaces of dust grains. These complex organics are of great interest to astrobiology, but are simpler than the molecules involved in biological processes. When ice-coated dust grains aggregate together in protoplanetary discs, and eventually in planetesimals, a large volume fraction remains unoccupied. The products of ice processing are retained within these cavities and subjected 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. Perhaps clusters of dust grains could be the mechanism of forming and transporting essential molecules to planet Earth.