User:PaulFleeman/Callisto (moon)

In recent years, attempts have been made to model Callisto’s atmosphere to gain better understanding of impact of collisional molecular interactions. The modelling of Callisto’s atmosphere consisted of a kinectic method to simulate the collisions that take place between the constituent elements of the moon’s atmosphere. Supported by NASA Goddard Space Flight Center’s Solar System Exploration Division, a team of researchers at the Center for Space Science at NYU Abu Dhabi simulated Callisto’s environments on a single component and multi-component basis of radiolytic volatile compounds. The constituent elements considered during the simulation are those previously mentioned and observed in Callisto’s atmosphere by the Hubble Space Telescope, comprised of carbon dioxide, molecular oxygen, and molecular hydrogen. Within the molecular kinetics model used for simulation, the seemingly high atmospheric density of Callisto can be described by the thermal accommodation and desorption of the compounds listed above. This thermal desorption is proposed to be a product of solar exposure, with high variation in temperature observed during the day and night cycle of the prospective moon. By using the direct simulation Monte Carlo (DSMC) method, energy exchange between dynamic molecular gas is evaluated with computational particle physics. Due to the transition from collisional to collision-less interactions, the DSMC method can describe Callisto’s atmosphere with relative accuracy. Each particle of the radiolytic volatiles were evaluated with factors such as initial position, velocity, and internal energy in mind. Given that the method is transient by nature, atmospheric collisions and thermal desorption take effect until each radiolytic volatile compound exhibits steady state properties at the macroscopic level. Radiative heating and cooling of the atmosphere is evaluated at noon and midnight, times that describe when the respective heat transfer are at the maximum for each end of the scale. It is important to note that these simulations are performed under the assumption that the carbon dioxide, oxygen, and hydrogen found in Callisto’s atmosphere thermally desorb into the moon’s regolith, and all thermal dynamics shown are only represented by molecular kinetic interaction. In an evaluation of the data presented throughout the simulation, the density of Callisto’s atmosphere can be described by the trapping of hydrogen gas by way of molecular interaction with the heavier gases, namely carbon dioxide and oxygen. The three radiolytic volatiles are presumed to be present throughout the moon’s surface and are expelled by means of thermal excitation. Once the compounds are heated, they begin to radiate outward from the surface of the moon. Due to hydrogen’s lighter nature, it is observed that it is the primary constituent involved in molecular collision, attempting to escape through the macroscopic cracks between the heavier constituents. This simulation provides closer insight into how these kinetic interactions between molecules influence the excitation of each constituent and how it affects Callisto’s atmosphere. Although the simulations are limiting in terms of variables considered, it is concluded that the molecular kinetics model used provides simulated densities that correlate to thresholds expected by means of experimental detection.