Correlating energetic neutral atom rates with solar wind pressure data to determine the scale of the heliosphere

The heliosphere is a vast region of space which surrounds the solar system and is created by the magnetic field of the Sun. The region inside the termination shock is a cavity in the magnetic field of the interstellar medium present outside the solar system, and has a “nose” and “tail” caused by the flow direction of the interstellar medium with respect to the Sun. Solar wind is the continuous flow of charged particles, produced by the Sun, which emanate outwards along the Sun’s magnetic field lines. When the solar wind reaches the termination shock, solar wind ions that neutralize in interactions with other particles are no longer bound to the magnetic field and follow ballistic trajectories as Energetic Neutral Atoms (ENAs). The Interstellar Boundary Explorer (IBEX) is a satellite which measures ENAs produced in the heliosheath which are directed back towards Earth. Changes in the solar wind pressure over time are reflected in ENA production in the heliosheath. Hence, by correlating ENA fluxes in a specific region of the sky with past solar wind pressure data, the time gap between changes in the solar wind pressure and returning ENA fluxes can be determined. By then analyzing the speed of the incoming ENAs, we can determine the approximate scale of the heliosphere and distance to the termination shock