Regional study of Ganymede’s photometry

Abstract

In this study, we present a regional photometric study of Ganymede’s surface to improve our understanding of its physical state. We created a comprehensive photometric dataset based on images taken with Voyager’s Imaging Science Subsystem and the New Horizons’ LOng Range Reconnaissance Image. We corrected for inconsistencies in the geometric metadata (camera position and orientation) and in the absolute calibration. We selected 20 regions of interest across the surface in different types of terrains. For each of them, we derived the Hapke model parameters using an inversion process based on a Monte Carlo Markov Chain in the Bayesian framework. Results are used to characterize surface properties in these different areas (single scattering albedo, roughness, shape of the grains from the phase function). We found that most general trends are consistent with past integrated studies. Ganymede has: (i) a slightly darker equatorial trailing hemisphere, (ii) a fairly elevated macroscopic roughness, (iii) a mostly backscattering behavior. However, we see an important diversity in the different regions we surveyed. We found a number of forward scattering regions both in the polar and equatorial regions that could be related to interaction with magnetospheric plasma but also be the sign of endogenic local activity. This gives us valuable insight in the preparation of ESA’s JUCIE mission whose main target will be Ganymede.