These reactions are important sources of species that are not synthesized efficiently by ion-molecule reactions, including the simplest hydrocarbons. Thus methane and acetylene, which account for a negligible fraction of the gas-phase carbon in cold regions, may be quite abundant behind a shock. Shocks also transform virtually all of the gas-phase oxygen into water. UV photons ionize most of the heavy elements, and this presumably has a significant affect on the gas-phase chemistry. The absorption of UV radiation by icy mantles on dust grains drives photolytic reactions which lead to the formation of organic material on the grain surfaces.
Shocks can vaporize dust grains.
Faster shocks can vaporize volatile organics, refractory organics, and even the refractory mineral cores of the grains. The goal of our research is to model the gas and grain surface chemistry of shock-heated material in the primitive solar nebula. Previous work on habitable zones around solar-type stars has been concerned primarily with the constraint that liquid water must exist on the surface of a planet suitable for life, a condition currently satisfied only by Earth in our own solar system. UV light may have had a profound influence on the early Earth environment, before the establishment of the ozone layer some 2.5Gyr ago. More generally, it is important to know UV flux levels at the surface and in the atmosphere of the primitive Earth, as UV radiation may be a vital energy source driving prebiotic chemical reactions.