A Solar Cycle of Observations with the Interstellar Boundary Explorer (IBEX)

The Interstellar Boundary Explorer (IBEX) was launched in 2008 and has now returned observations over a full 11-year solar cycle (Solar Cycle 24). IBEX remotely images global ion distributions via charge exchange Energetic Neutral Atoms (ENAs) propagating inward from the heliosheath – the region between the termination shock and heliopause – and beyond. These observations have led to numerous discoveries about the outer heliosphere and its interaction with the surrounding interstellar medium. Heliospheric ENAs arise largely from two sources: the IBEX Ribbon, which is likely generated beyond the heliopause, in the very local interstellar medium, and the globally distributed flux (GDF), which is primarily produced in the heliosheath. In this talk we summarize some of the critical advances driven by IBEX observations. We also examine how the heliosphere and its interstellar interaction have evolved over the past solar cycle. For most of IBEX’s 11 years of observations, there was an overall reduction and then flattening of the ENA fluxes at all energies, consistent with a generally deflating, or shrinking, heliosphere. Over the past few years, IBEX has been observing the progressive response of the heliosphere to a large persistent increase in the solar wind output that passed 1 AU in the second half of 2014. This enhancement arrived at the outer heliosphere as indicated by an increase in the ENAs returning from the closest region of the inner heliosheath, south of the upwind direction, starting in the second half of 2016. Since then, the region of enhanced ENA emissions has expanded progressively outward from there, exposing increasingly further away regions of the heliosheath. IBEX observations over the past 11-years have led to a true scientific revolution in our understanding of the outer heliosphere and its interstellar interaction.