IBEX’s sole, focused science objective is to discover the global interaction between plasma from the solar wind and the interstellar medium at the boundary region of our Solar System. IBEX achieves this objective by detecting energetic neutral atoms (ENAs) coming from the boundary region and interstellar neutral atoms coming inward from outside the boundary. From these detections, IBEX scientists hope to answer four fundamental science questions:
- What is the global strength and structure of the termination shock?
- How are energetic protons accelerated at the termination shock?
- What are the global properties of the solar wind flow beyond the termination shock and in the heliotail?
- How does the interstellar flow interact with the heliosphere beyond the heliopause?
The heliosphere helps define one type of boundary of our Solar System. The solar wind from our Sun blows outward against the material between the stars, called the "interstellar medium", and clears out a bubble–like region. This bubble that surrounds the Sun and the Solar System is called the "heliosphere." It is a definable, measureable region in space. The use of the word "global" above means "as seen around the entire sky." The "termination shock" is the region where the solar wind slows down and begins to interact with the interstellar medium. The "heliotail" is the region of our heliosphere opposite to the direction of travel of our Solar System through the Milky Way Galaxy. The part of our heliosphere in the direction of travel is often called the "nose." The "heliopause" is the outermost boundary, where the solar wind does not travel outward any farther.