Physical chemistry of protoplanetary disks

Studying protoplanetary disks and their dust content is crucial for understanding the processes leading to the formation of planets. Protoplanetary disks result from the conservation of angular momentum in a collapsing, rotating cloud of gas and dust. Typical dimensions of these disks are of the order of a few 100 AU (1 AU= 149.60 x 106 Km) with lifetimes of 1-10 Myr. Solar system bodies such as planets, meteorites and comets are all created from solids during the protoplanetary disk phase. The physical conditions in the disk, like temperature, pressure, density, heating and cooling processes, together with dynamical processes such as turbulence, radial mixing, inward accretion and outward jet flows, determine a wide range of thermodynamic conditions in which the first grains condense out of the gas phase. The processes of grain formation are then intrinsically related to the chemistry of the disk. Indeed, the materials that form in the disks are a mixture of condensates with different chemical compositions and properties, reflecting the wide range of physical conditions in the disk. The quantity and quality of observations of disks around young stars has increased in recent years: the Spitzer space telescope and the new Herschel space telescope have provided a large amount of useful data at infrared wavelengths, whose interpretation provides information on the composition, growth and thermal processing of dust grains in the disk. Together with these observations, the study of objects in our solar system provides direct and accessible evidence of the chemistry of the young solar system and the thermodynamic condition in which they formed.