Solar Orbiter Neutral Solar Wind Detector

Neutral hydrogen atoms, which give rise to the prominent so lar Ly-alpha corona, are closely coup led to the emerging solar-wind plasma. The density ratio of neutral hydrogen to protons is minute, ~10-6; therefore, the neutral atoms are tracers in the solar wind. In-situ observations of the neutral atoms, their flight paths (imag ing), density, and velocity distribu tions are a new tool to the understanding of the Ly-alpha corona, i.e. setting limits on the plasma velocity distribution along the solar magnetic field lines. The other goal of the neutral solar- wind instrumentation is the in-situ observation of the interactions between solar wind plasma and dust grains near the Sun. We will discuss the science objectives and the potential "zero charge" solar-wind instrument envelope onboard Solar Orbiter.