Master thesis defense by Jacob Krag Nørgaard

Recent observations of protoplanetary disks with telescopes and interferometers such as the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA) reveal a wide range of water, carbon dioxide, and hydrocarbon abundances.

These findings have been linked to volatile ice lines, disk substructures, and the disk’s temperature structure. In this thesis, we aim to broaden our understanding of how evolving disk parameters such as temperature, the vapor reservoir, and dust size distribution can influence the ice lines and phase transitions of volatiles.

For this purpose, a one-dimensional gas-dust-vapor-ice model, including viscous and diffusive gas and dust evolution, dust drift, collisional evolution of solids, and volatile-phase changes, was built into the simulation framework DustPy. Simulations with the model show that the coupled evolution of dust and vapor controls the evolution of water. In the fiducial model, destructive collisions keep water release localized near the ice line, while removing fragmentation and erosion allows larger icy particles to enrich the inner vapor reservoir, in some cases moving the sublimation regime.

A luminosity burst-type heating event shows that temporary heating can shift the ice line outward and leave a long-lived, grain-size-dependent imprint as vapor recondenses mainly onto small grains. This work demonstrates that simplified descriptions of the volatile ice line as temperature-defined boundaries miss important aspects of disk evolution. The distribution of water ice and vapor is history-dependent, meaning that the volatile composition observed at a given time may reflect earlier stages of dust growth, transport, and heating.

These results highlight the need to treat dust and volatile evolution self-consistently when assessing the volatile material available for planet formation.

Supervisors

Troels Haugbølle, Adrien Houge, Michael Küffmeier, and Giulia Perotti

Censor

Hans Kjeldsen, AU