Simulating Observations of Ices in Protoplanetary Disks

Ices play an important role in protoplanetary disks by facilitating grain growth and planetesimal formation, while ices sequestered in planetesimals may subsequently deliver bio-critical volatiles to potentially habitable planets. Comparing disk ice abundances with cometary values will reveal whether the chemical inventory of our solar system is unique or common. Measuring disk ices can also reveal the degree to which the molecular abundances of planetary systems are inherited from their protostellar environment or reset by disk processes. Various ice species (e.g., H₂O, CO, CO₂, CH₃OH, NH₃, CH₄) can be identified via absorption features in the near- and mid-IR. The upcoming James Webb Space Telescope (JWST)—due to its high sensitivity and spectral resolution at these wavelengths—is poised to significantly advance observational studies of protoplanetary disk ices. We present simulated JWST observations of disks to assess which ice features can be observed under various disk conditions and what can be learned about protoplanetary disks and planet formation from such observations. To do so, we first use a radiative transfer simulation to derive the temperature and radiation field throughout the disk for a specified dust and gas distribution. We then use a time-dependent gas-grain chemical model to simulate the distribution and abundances of ices within the disk. Finally, we use laboratory-measured optical constants of the dominant ice species plus radiative transfer modeling to simulate observations of the disk with JWST.