Astrochemical Modeling Of Dust Grain And Cometary Ices 137 views

Chemical models have long been useful tools to study various astronomical environments. These models can provide insight that can assist in both observations and experiments. One such instance is with interstellar dust grains and the effects of grain porosity. The degree of porosity in interstellar dust-grain material is poorly defined, although recent work has suggested that the grains could be highly porous. Aside from influencing the optical properties of the dust, porosity has the potential to affect the chemistry occurring on dust-grain surfaces, via increased surface area, enhanced local binding energies, and the possibility of trapping of molecules within the pores as ice mantles build up on the grains. Using the microscopic Monte Carlo chemical kinetics model MIMICK, we construct dust grains atom by atom and allow adsorption from the gas-phase to build up an ice layer. From this, we investigate the physical and chemical effects that a porous and a non-porous grain have on the composition and structure. Chemical models of cometary ices are also exceptionally rare. We build on previous work, using the rate equation chemical kinetics model MAGICKAL, and improve on previous functions in an attempt to model more complex environments that a comet may experience. We start by modeling Comet Hale--Bopp, a long period comet. Here we include functions to model the active phase of a comet. Then we move onto a short period comet, 67P/Churyumov–Gerasimenko, allowing for more complex initial ices and including factors for solar UV and protons on the ice. Finally, we add in additional functions allowing for dust grain buildup on the surface and add in a dust loss factor. Using this final model, we attempt to model the chemical effects highly energetic events external to the solar system, such as passing hot stars and nearby supernovae, have on the chemistry of cold storage comets.

PHD (Doctor of Philosophy)

astrochemistry; interstellar dust; comets; ices; Comet Hale-Bopp; Comet 67P/Churyumov–Gerasimenko; chemical kinetics model; supernovae

English

2024-07-31