interplanetary medium - interplanetary space including forms of energy and gas and dust

solar wind - a stream of protons moving radially from the sun

plasma - (physical chemistry) a fourth state of matter distinct from solid or liquid or gas and present in stars and fusion reactors; a gas becomes a plasma when it is heated until the atoms lose all their electrons, leaving a highly electrified collection of nuclei and free electrons; "particles in space exist in the form of a plasma"