Science Opportunities from Simultaneous Observations of the Heliospheric Hydrogen and Helium Backscatter Glows

The heliospheric resonant backscatter glows of interstellar hydrogen and helium provides important information on the physical state of interstellar gas on one hand, and on ionization processes inside the heliosphere on the other hand. The hydrogen glow traces the distribution of interstellar neutral H (ISN H), which is sensitive to the latitudinal structure of the solar wind density and velocity. The distribution of ISN He near the Sun is determined on one hand by solar EUV photo ionization, and on the other hand by solar electron impact ionization. Here, we demonstrate that with simultaneous measurements of both H and He glows from carefully selected regions in the sky it is possible to investigate the radial and latitudinal structure of the solar wind and the structure of the electron temperature near the Sun. We show the expected effect of the solar wind structure on the helioglows of H and He and the expected helioglows variations during the cycle of solar activity. For the first time, it will be shown that with the latitudinal structure of the solar wind obtained from the hydrogen glow it is possible to investigate the solar wind electron temperature at all heliolatitudes within 1 AU from the Sun by analysis of the helium glow around the Sun. Comparing glows observations with model predictions enables to fix global solar wind electron properties. Such a study would be a first in the history and provide an important complementary information for the planned in situ measurements by Solar Probe, Solar Orbiter and IMAP.