Authors: Daniel B. Reisenfeld (Los Alamos National Laboratory), Maciej Bzowski (Space Research Center, Warsaw, Poland), Herbert O. Funsten (Los Alamos National Laboratory), Jacob Heerikhuisen (University of Waikato, New Zealand), Paul H. Janzen (University of Montana), Marzena A. Kubiak (Space Research Center, Warsaw, Poland), David J. McComas (Princeton University), Nathan A. Schwadron (University of New Hampshire), Justyna M. Sokol (Southwest Research Institute), Alex Zimorino (University of Montana), and Eric J. Zirnstein (Princeton University)

For the first time, we have mapped the 3D structure of the heliosphere using ENA flux observations from the Interstellar Boundary Explorer (IBEX) mission.  IBEX has shown that variations in the ENA flux from the outer heliosphere are associated with the solar cycle and longer-term variations in the SW. In particular, there is a good correlation between the dynamic pressure of the outbound SW and variations in the later-observed IBEX ENA flux. The time difference between observations of the outbound SW and the heliospheric ENAs with which they correlate ranges from approximately two to six years or more, depending on ENA energy and look direction. This time difference can be used as a means of “sounding” the heliosheath, that is, finding the average distance to the ENA source region in a particular direction.  We have applied this method to build a three-dimensional map of the heliosphere. We use IBEX ENA data collected over a complete solar cycle, from 2009 through 2019, corrected for survival probability to the inner heliosphere. We divide the data into 56 “macro-pixels” covering the entire sky, and as each point in the sky is sampled once every six months, this gives us a time series of 22 points per macro-pixel on which to time-correlate. Consistent with prior studies and heliospheric models, we find that the shortest distance to the heliopause d_HP is slightly south of the nose direction (d_HP ~ 110 – 120 au), with a flaring toward the flanks and poles (d_HP ~ 160 – 180 au).  The heliosphere extends at least ~350 au tailward, which is the distance limit of the technique.