The presence of water ice both on the surface and in the subsurface of planetary bodies, like Ceres, Moon and Mercury has been demonstrated in recent studies. In particular, water ice is present in some permanent or semi-permanent shadowed areas, for example on the rims of craters, where the local topography and illumination conditions favour the presence of perennial water ice. The presence of water ice not only has great significance from an astrobiological point of view, but it also provides important information about a body’s internal evolution. For these reasons, it is critical to evaluate the stability of water ice on the surface or in the shallow subsurface of planetary bodies. Wherever ice is unstable, for example due to the local illumination conditions or to impact events, it can lead to the formation of a transient exosphere.
The scientific literature offers a wide range of one dimensional thermophysical models. However, no complex numerical modeling has integrated an Eulerian approach, which provides a complete thermophysical representation of the simulated sites, with a Lagrangian approach, which simulates the likely water vapour emission, as well as the interaction of volatiles with the regolith (dust). A rigorous study of the evolution of a mixture of vapour-ice particles emitted by the surface is motivated by two aspects: I) water emissions can be observed as transient phenomena; II) the pressure and temperature conditions present allow for processes of both sublimation and recombination.
This research project aims to bridge this gap with the following three-pronged approach:
- Application to representative ice-rich sites on Moon, Ceres and Mercury by (a) preparing the digital terrain model (DTM) in a specific format compatible with the above numerical modeling, and (b) calculating the corresponding illumination conditions. Temperature maps of the surface/subsurface as a function of thermal inertia will be used to evaluate the lifetime of surface ices.
- Application of a 3-D finite element method (FEM) thermophysical model, based on digital terrain models (DTM) and illumination conditions at reference sites.
- Implementation of a code based on the Smoothed Particle Hydrodynamics (SPH) scheme to study the water vapour emission and the volatile-dust interaction, given the temperature maps produced by the FEM model. Water vapour emission may be triggered both by the local illumination and by impact events.
- This synthetic description of the physical characteristics of ice-rich areas on planetary surfaces will provide critically-needed theoretical support both to recent and current space missions (e.g. Dawn, Rosetta, BepiColombo, ExoMars) and to future missions. Ice-rich areas on the Moon, for example, are primary targets for future human exploration.