PhD ceremony Mr. G. Chaparro Molano: The cosmic-ray dominated midplane of protoplanetary disks. The solar system connection

PhD ceremony: Mr. G. Chaparro Molano, 11.00 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: The cosmic-ray dominated midplane of protoplanetary disks. The solar system connection

Promotor(s): prof. I. Kamp

Faculty: Mathematics and Natural Sciences

I set out to constrain the chemical conditions in the early Solar System by analyzing chemical evolution models of protoplanetary disks and comparing them to our current knowledge of Solar System bodies, such as comets. For this I require a 2D radiative disk model in vertical hydrostatic equilibrium to set the conditions in which the chemistry evolves. Given that the planet (and comet) forming region of disks coincides with the cosmic-ray dominated midplane of disks, I focus on understanding the role of cosmic ray-induced photoprocesses, treating them in a way that is consistent with the local dust and gas opacity.

I find that gas opacity in gas-rich regions of the disk midplane is a major contributor to the total opacity. Gas species formed in this region that drift vertically to optically thin zones may be used to probe the midplane chemical activity. I find that cometary ice species are formed in timescales shorter than the lifetime of the disk, thus showing that steady-state chemical models underpredict those abundances. I propose that regions located at r > 10 AU are ideal for the formation of ice mantles that match observed cometary abundances and ice-to-dust mass ratios. I discuss the possibility of trapping ice species formed in early stages of the disk evolution, thus forming a stratified ice mantle. The growth of an ice mantle contributes to increase significantly the size of dust grains. Such a modification in the dust size distribution will impact the midplane temperature and the efficiency of dust coagulation.