NASA | IBEX: Observing the Sun's Horizon

The Interstellar Boundary Explorer, or IBEX, is the first mission designed to map the entire region of the boundary of our Solar System. As charged particles from the Sun, called the "solar wind," flow outward well beyond the orbits of the planets, they collide with the material between the stars, called the "interstellar medium" (ISM). These interactions create energetic neutral atoms (ENAs), particles with no charge that move very quickly. This region emits no light that can be collected by conventional telescopes so, instead, IBEX, measures the particles that happen to be traveling inward from the boundary. IBEX contains two detectors designed to collect and measure ENAs, providing data about the mass, location, direction of origin, and energy of these particles. From these data, maps of the boundary are created. IBEX's sole, focused science objective is to discover the nature of the interactions between the solar wind and the interstellar medium at the edge of our Solar System.