Variation in Phobos geophysical properties using different shape models and dynamic Voxel mascons

ABSTRACT Phobos, the larger Martian moon, shows a low bulk density indicating substantial internal porosity and possible water-ice content. Its pronounced proximity to its parent planet, an unusual low albedo, and its orbital configuration raise unresolved questions regarding its formation mechanism, while its internal structure remains poorly constrained. Recent space missions have provided critical data, but precise constraints on the mass distribution and internal composition are lacking. A detailed gravitational field mapping of Phobos could serve as a potential pathway to constrain them. This study compares two shape models of Phobos, for different discretization methods. For both models a Voxel-based mascons representation for different edge lengths are generated. We investigate the influence of the shape model, the choice of the discretization algorithm, and the resolution for the surface gravitation, the gravity coefficients, the moments of inertia, and libration amplitude assuming a homogeneous density. Subsequently, we model heterogeneous mass distributions based on segmented and unsegmented Perlin noise and evaluate the associated properties. All models accurately reflect the properties within the numerical uncertainty, while one shape model shows a significantly better agreement for the numerical deviation of Phobos surface gravitation assuming homogeneous density. Perlin noise-based density distributions show striking similarity to rubble-pile configurations and cannot be ruled out using the current measurement data. Our findings emphasize the dependency between shape model quality and interior characterization, providing a framework for optimizing observational strategies to constrain Phobos’ origin.