Degree: Master of Science Abstract: In the development of a numerical model for the water cycle on Mars, adsorption of water vapour in the Martian regolith acts as a significant sink and retards the transport of mass. Adsorption on Mars cannot be studied directly, so a numerical model was created, and a diffusion sorption experiment was devised using silica gel beads and water vapour to validate the model. In literature, the Local Instantaneous Equilibrium Adsorption (LIEA) assumption is often invoked, and here it is compared to a non-instantaneous form of the mass conservation equation, that uses a concentration dependent flux term to model the rate of adsorption. An analysis of the Damkohler number proves to be a reliable predictor of whether the LIEA assumption is appropriate. Adsorption is also shown to be strongly dependent on the porosity, and bulk density of the medium, as well as the temperature of the system.