The Evolution of Volatile Carbon During Planet Formation

Planets are formed in protoplanetary disks of gas and dust around young stars. Where and when a planet forms determines its ultimate composition. However, our ability to determine exoplanet compositions from observations is extremely limited. To truly understand what planets are made of we must instead observe the planet-forming material in the natal disk. In this talk I will discuss recent Atacama Large Millimeter/submilliter Array observations of molecular line emission which reveal low abundances of gas phase carbon in protoplanetary disks. This volatile sequestration, i.e., the removal of molecules such as CO from the gas, can occur via chemical reprocessing into less volatile species or trapping as ice in large dust grains or planetesimals. Using disk chemical modeling, I will demonstrate that under most physical conditions both chemical and physical processes likely play a role in removing carbon from the gas on short timescales. I will then present ways to test various predictions regarding mechanisms to remove gas phase carbon and  determine the dominate volatile carbon reservoir in planet-forming disks.