Building A 3-D Map of the Heliosphere with IBEX

The IBEX mission has shown that variations in the ENA flux from the outer heliosphere are associated with the solar cycle. In particular, there is a good correlation between the dynamic pressure of the outbound solar wind and variations in the observed IBEX ENA flux. (McComas et al. 2017, 2019; Reisenfeld et al. 2016) There is, however, a time difference between observations of the outbound SW and the heliospheric ENAs with which they correlate, ranging from approximately two to six years, 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 use IBEX ENA data collected over a complete solar cycle, from 2009 through 2019, corrected for survival probability to the inner heliosphere (Bzowski, 2008), and divided into 55 "macro-pixels" covering the entire sky. Because 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. Using this technique, we have created a global 3-D "map" of the heliopause. Consistent with heliospheric models, we find that the shortest distance to the heliopause is slightly south of the nose direction (d_HP ~ 115 - 125 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 effective distance limit of this technique.