interplanetary medium

The medium between the planets in the solar system composed of interplanetary dust, electrically charged particles from the Sun and neutral gas from the interstellar medium. The charged particles consist of electrons, protons and helium nuclei (alpha particles) streaming outwards from the Sun and forming the solar wind. Atoms of neutral hydrogen and helium gas are also present, replenished from the interstellar medium in the Sun's vicinity. Under the influence of solar ionizing radiation, these atoms have a lifetime against ionization of only twenty days at the Earth's distance from the Sun.