Potential Observations of the Solar Atmosphere via In-Situ Measurements of the Neutral Solar Wind

Neutral hydrogen atoms are closely coupled to the emerging solar wind plasma. They give rise to the prominent solar Ly-alpha corona. The ratio of the densities of neutral hydrogen and protons is very small, some parts per million, and the neutral atoms are therefore a trace particle population in the solar wind plasma. In-situ observations of the neutral atoms, their flight paths (imaging), densities and velocity distributions might help to redefime the understanding of the Ly-a corona, i.e. setting limits on the plasma velocity distribution along the solar magnetic field lines. We will discuss the gain and limitations of such observations and potential neutral solar wind instrumentation on Solar Orbiter.