Structure of the Heliotail from Interstellar Boundary Explorer (IBEX) Observations: Implications for the 11 Year Solar Cycle and Pickup Ions in the Heliosheath

The interaction of the solar wind (SW) and local interstellar medium (LISM) forms a dynamic region in space known as the heliosphere. At 100 AU from the Sun, the supersonic SW plasma is slowed, compressed and heated at the termination shock, creating a suprathermal ion population in the inner heliosheath (IHS) whose properties can be revealed by the Interstellar Boundary Explorer (IBEX). IBEX measurements of energetic neutral atoms (ENAs) from the heliotail show a multi-lobe structure of ENA fluxes as a function of ENA energy from 0.71 to 4.29 keV. Below 2 keV, there is a single lobe of enhanced ENA fluxes centered near the downwind direction. Above 2 keV, this structure separates into two lobes north and south of the solar equatorial plane. This is interpreted as originating from the fast and slow SW propagating through the IHS. One model suggests that the heliotail splits into a crescent-like shape, and is responsible for the two lobe ENA structure. Here we present results from a time-dependent simulation of the heliosphere that produces a comet-like heliotail, and show that the 11 year solar cycle is responsible for the formation of the ENA lobes observed by IBEX. Moreover, we demonstrate that the energy-dependent extinction of pickup ions due to charge-exchange in the IHS is an essential process required to create the global ENA structure. However, our results reveal a global underestimation of the observed ENA fluxes, strongly suggesting that a key process is currently missing in our understanding of the IHS plasma.