The overarching goal of the proposed ISSI team is to update the boundary conditions for models of exospheres in direct contact with planetary surfaces using atomistic and granular simulations. We will investigate using a multi-scale approach to improve model predictions or key species in the exospheres of airless bodies such as the Moon and Mercury. The work will create higher-fidelity physical models of gas trapping, diffusion, and emission within the first top few centimeters of regolith. The outputs assist efforts to use existing and/or future measurements to characterize and better understand the composition and evolution of the exospheres on airless bodies such as the Moon and Mercury.
In specific, we will use modelling on different dimensional scales to study the underlying physics and energetics of key ejection processes on the surfaces of airless bodies and how they affect their predicted global exosphere. Here, we will use molecular dynamics (MD) simulations to study these processes on the atomistic scale as a function of surface composition, surface energetics (bond state and crystallinity) and emitted atom type. We will then incorporate these MD-derived parameters into granular-scale models to quantify the effect of the planetary regolith, retention, and emission processes. We will then incorporate these granular-scale results into global exosphere formation model to quantify the effects of gas-surface interactions on the predicted exospheres of the Moon and Mercury.