Spacecraft Missions (cont.) IBEX (Interstellar Boundary EXplorer) is a small explorer NASA mission to map the boundary of the Solar System. The spacecraft is a small satellite the size of a bus tire. IBEX will observe the Solar System Boundary while in orbit around Earth. It launched in October 2008 from the Marshall Islands on a Pegasus rocket. It has "telescopes" that are looking out towards the edge of the Solar System. However, these telescopes are different than most telescopes. They collect particles instead of light. These particles are called energetic neutral atoms (ENAs). The ENAs will provide information about the Solar System’s boundary by traveling toward Earth from beyond the orbit of Pluto. The particles travel for as little as a month to up to 11 years to complete the journey. By collecting these particles, scientists can make the first map of the boundary of the Heliosphere created by the interaction between the solar wind and the interstellar medium.