Vol. 534
In section 6. Interstellar anc circumstellar matter

The chemical history of molecules in circumstellar disks. II. Gas-phase species

Understanding the chemistry of disks around young stars is fundamental for understanding the current physical conditions in such disks, and it gives us a guide to the formation and constitution of solar system bodies such as comets. The chemical composition, on the other hand, depends on the detailed history of protostellar collapse and disk formation. In this article, the authors follow the chemical evolution of parcels of gas which eventually end up in the disk. They find, for example, that comets probably form from material with differing chemical histories, so it is not surprising to find large variations in cometary composition.