Super-resolution maps of icy moons: Application to the Cassini-VIMS observations of Enceladus

The icy moons of the outer solar system (Ganymede, Enceladus, Titan, etc.) have been found in the forefront of planetary exploration, due to their diverse geomorphology coupled with numerous discoveries hinting to possible habitable conditions: geothermal activity, oceans of liquid water under the ice crusts, abundance of volatiles, and in some cases complex organics, to name a few. Of paramount importance for constraining the internal structure and properties of these bodies are high-precision cartographic products, allowing for linking surface morphologies and composition to internal activity. These cartographic products are constructed by reconciling numerous different observations, which, due to the complexities of an orbital tour, are recorded under a great range of different illumination and observation conditions, with varying spatial sampling. The aim of this study is to provide to the community a complete pipeline for producing super-resolution (SR) maps for icy moons, by combining all the overlapping observations for a specific target. The development and testing of our pipeline are carried out using the hyperspectral cubes recorded by the Visual and Infrared Mapping Spectrometer (VIMS) instrument, on board the Cassini Saturn orbiter, during its 13-year long investigation of the Saturn system that ended in 2017. We focus our efforts on Enceladus, a prime astrobiological target, which contrary to Titan does not possess a thick atmosphere, the influence of which needs to be removed from the data before implementing the super-resolution methodology for surface cartography. We first navigate the data, calculating accurate projections that can be combined into global mosaics of Enceladus. We then implement a global photometric correction model that compensates for the different acquisition conditions, allowing for the construction of global mosaics with diminished visible seams, improved homogeneity at the global scale and sharper definition of surface features at the local scale. In the third step of our methodology, we combine all the overlapping observations of the same area to calculate the new SR maps of Enceladus in the infrared. Utilizing the new, SR global map of Enceladus, we provide new insight into the moon’s geomorphology as revealed from its surface spectral heterogeneity, demonstrating the capability of the SR approach to augment our understanding of existing data sets of icy moons and help prepare for future observations.