The role of cosmic rays in setting the chemical content of protoplanetary disk midplanes
Abstract
The chemical evolution of volatiles in protoplanetary disks begins in the earliest prestellar phase of star formation. Under the dark, cold conditions of cores the initial icy mantles of grains are built up. Already at this point, grain-surface chemistry starts to set the composition of these icy layers. Cosmic rays play a pivotal role here by setting the abundances of radicals available for the synthesis of more complex molecules and also for maintaining low abundances of gaseous molecules directly via spot heating and indirectly via reactive desorption. Protoplanetary disks are built up from the collapsing core materials, which are exposed to variable intensities of UV irradiation and heating. Cosmic rays continuously play a sub-dominant role in chemical processing during the collapse of the system and also in the outer, lower density regions of disks. Only in the innermost, high-density regions do they become attenuated. In this talk, the history of the protoplanetary disk composition will be unraveled with the help of sophisticated physicochemical models for a range of cosmic ray ionization rates (expansion of Drozdovskaya et al. 2014, 2016). The models will be used to access the degree of importance of cosmic rays in setting the abundance of volatiles in protoplanetary disk midplanes. Cometary data will be contrasted against the modeled volatile quantities, taking into account a range of possible cosmic ray ionization rates.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E.897D