Abstract

Planets are built from material – dust, gas, and ice – in the dense, dark, and relatively cool midplanes of protoplanetary disks. There currently exist two schools of thought on the composition of disk midplanes and thus planet-building material. The first, and perhaps most intuitive, is that the midplane has a fixed composition that varies only across snow (or ice) lines that mark the boundary beyond which a particular volatile exists solely in the ice phase. This assumption is widely invoked in the exoplanet community to relate observed atmospheric abundances to a formation location and also by the planet population synthesis community to set the initial composition of planetesimal ‘seeds’. The second considers alteration of the composition of planet-building material via chemical reactions in the gas and on the surfaces of small dust grains (<~ 1 mm). This can occur during the disk formation stage (from cloud to disk), and during protoplanetary disk evolution and dispersal (from disk to planet). Hence, to what extent chemistry affects the composition of planet-building material depends upon the timescale of planetesimal growth relative to the timescale of disk formation and dispersal. In this talk, I will show results from chemical kinetics calculations of protoplanetary disks to illustrate the effects of chemistry on the composition of planet-building material during disk formation and evolution.