Imaging the three‐dimensional solar wind

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Abstract
Charge exchange collisions between the solar wind alpha particles and heliospheric atomic hydrogen produce a unique emission in the 30.4‐nm line. We demonstrate that an all‐sky image in this emission would reveal the three‐dimensional flow properties of the solar wind, including the flow properties in the regions over the Sun's poles and on the far side of the Sun. The boundary separating the fast (high‐latitude) and slow (low‐latitude) solar wind can be established remotely, from 1 AU. Most of the observed 30.4‐nm emission would originate in the region extending up to 10 AU from the Sun. Solar wind flow velocities can be obtained both from radiance directional dependence (images) and directly from the Doppler shifts. The fast and slow solar wind flows would produce emissions spectrally separated by ∼0.03 nm (∼0.3 Å). The feasibility of solar wind imaging depends on the spectral properties and relative strength of the background radiation. The main background sources include galactic diffuse and stellar radiation, glow of the interstellar plasma beyond the heliopause, and glow of the solar wind pickup ions. We show that the solar wind emissions are clearly spectrally separated from the background radiation. Metastable single‐charged helium ions would also be produced in the solar wind charge exchange collisions. Two‐photon decay of these ions would dominate in many directions the continuum extreme ultraviolet background at 1 AU in the 30–90 nm spectral range.