Planetary Group Seminar: The chemical heritage of protoplanetary disks (C. Walsh)

Protoplanetary disks are the birth sites of planets and planetesimals such as comets. Gas and ice chemistry during protoplanetary disk formation and evolution determines the composition of planet- and comet-building material, the study of which is important for gaining insight into our origins. In recent years, our understanding of the chemical composition and structure of nearby disks has advanced significantly. The Atacama Large Millimeter/Submillimeter Array (ALMA) has revealed the dust and gas structure of disks at (sub)mm wavelengths with unparalleled resolution. In addition, the Rosetta mission is measuring the composition of comet 67P/C-G in situ with unprecedented accuracy. The cometary material is likely representative of that in the natal protoplanetary disk around the young sun. In this seminar, I will discuss the various chemical processes which occur in protoplanetary disks and their relative importance in determining the composition of the planet- and comet-building material. I will discuss the results of protoplanetary disk models in light of observational results which probe the composition of the disk. I will also describe the potential formation routes and observability of small, simple and abundant molecules (e.g., CO, H2O, and CO2), and also so-called "complex organic molecules" (e.g., CH3OH), species which are thought to be the precursors of molecules important for prebiotic chemistry. The detection of such molecules in disks provides a vital link between the composition of the material observed towards the hot environs of protostars and that seen in comets, strengthening the hypothesis that planet-building disks have inherited a significant fraction of their material from earlier stages in the star formation process.