IBEX's sole, focused science objective is to discover the global interaction between the solar wind and the interstellar medium. IBEX achieves this objective by taking a set of global energetic neutral atom (ENA) images that 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?
IBEX measures Hydrogen ENAs generated predominantly in the inner heliosheath by solar wind protons, pickup protons, and energetic protons. The image to the left shows the various regions and boundaries of our heliosphere:
- Termination Shock: Where the solar wind transitions from a fast supersonic wind to a slower subsonic flow.
- Hydrogen Wall: Near the nose of the outer heliosheath where the interstellar ion flow slows, heats, and piles up as it deflects about the heliopause. A large portion of interstellar H atoms charge-exchange with piled-up protons, causing a similar pile-up of H atoms.
- Heliopause: Separates the subsonic flow of solar wind (inner heliosheath) from the slowed, heated, and diverted interstellar flow (outer heliosheath).
- Bow shock or wave: Separates undisturbed interstellar flow from the slowed heated and diverted interstellar flow.