Extreme-ultraviolet diagnostics of pick-up ions in regions close to the solar corona I. Feasibility of new observations

Recent investigations of pick-up ion data obtained with the AMPTE and the Ulysses spacecraft resulted in the discovery that, in contrast to previous expectation, pick-up ion velocity distribution can be anisotropic. Such anisotropy results from a smaller efficiency of pitch-angle scattering than usually assumed and translates into a larger scattering mean free paths than previously attributed to these particles. We demonstrate that existing and upcoming in-situ observations can be substantially supplemented by Earth-bound observations of the extreme-ultraviolet resonance glow of pick-up ions in the vicinity of the sun. The proposed observations, in combination with a theory of ions being picked-up by the heliospheric magnetic field close to the sun will not only allow us to obtain information about the anisotropy of the pick-up ion velocity distributions, but also to deepen our understanding of the physics of the accelerated solar wind and of the pick-up process of ions in this innermost region of the heliosphere not yet well explored.