Project 5

Nitrogen is abundant as a solid ice on the surfaces of Triton and Pluto. It supports their thin atmospheres via vapor pressure equilibrium. Surfaceatmosphere interactions are key to the weather and climate cycles on Pluto and Triton, as well as the formation and evolution of landforms related to sublimation, condensation, and glacial flow of volatile ices. But N2 is also accompanied by CO and CH4, both with lower vapor pressures than N2. How they influence the mobility of N2 constitutes a critical knowledge gap. To reach thermodynamic equilibrium requires mobility of molecules within the solid state. If solid state molecular diffusion is slow, the interiors of surface particles may remain perpetually out of equilibrium, unable to keep up with diurnally changing insolation. Everything depends on how rapidly molecules can diffuse through the various volatile ice phases that exist at Pluto and Triton. This project will employ all-atom molecular dynamics simulations of ice mixtures. These simulations generate trajectories at specified temperatures, pressures, and compositions representative of Pluto and Triton surface conditions, in both bulk crystalline phases and at crystal–vapor interfaces. Analysis of molecular displacements and hopping events within the solid allows transport to be quantified and linked to underlying lattice fluctuations and defects. These simulations provide microscopic insight into the mechanisms of solid-state molecular diffusion and directly inform interpretation of laboratory measurements performed by collaborators Drs. Grundy and Hanley.

The student will perform molecular dynamics simulations and learn to interpret the results. A typical commitment would be 10 hours/week. They will
become proficient with Monsoon (NAU’s high performance computing cluster), computational chemistry software, and python script to analyze the
results. The student will be encouraged to attend and participate my weekly group meetings and the weekly Ice Lab meetings, a collaboration around this
and related topics.

At a minimum, the student will participate in the NAU Undergraduate Research Symposium. This project represents one piece of a burgeoning
collaboration between Drs. Grundy and Hanley (Lowell Obs) and me, so I expect these results will be important foundation for that project and contribute to presentations and publications, complimenting laboratory data.