Irradiation effects on comets and cometary debris

Experimental results obtained over the past 10 years on the chemical and physical changes induced by ion and electron irradiation of materials relevant to comets are reviewed, and their physical interpretation and their relevance for cometary astrophysics are addressed. Four phases of the irradiation history are considered: the precometary phase, the accretion phase, the cometary phase, and the postcometary phase. The relevant applications of laboratory results are reviewed. The ability of ion irradiation of simple carbon-containing ices to produce complex refractory organic materials is discussed. In the Oort cloud, this process can occur several meters into the surface, so that the buildup of a stable organic crust may occur. Ion irradiation at various stages is compared with other models for the production of organics.