Cassini as a heliospheric probe—the potential of pick-up ion measurements during its cruise phase

Measurements of the spatial distributions of pick-up ions can be utilized to infer important information about the structure of the heliosphere. First, a determination of the symmetry axis of flux distributions of pick-up ions not experiencing any significant filtration of their neutral parent atoms in the heliospheric interface represents a new method to derive the orientation of the upwind-downwind axis of the heliosphere from observation. Second, a comparison of pick-up ion flux distributions resulting from neutrals both filtered and not filtered during their passage through the heliospheric interface might provide insight into the geometry of the interface and, subsequently, give information about the strength and orientation of the local interstellar magnetic field. A feasibility study for carrying out such measurements with the Cassini spacecraft is presented, and the most promising pick-up ion candidates are identified.