Abstract
The Interstellar Boundary Explorer (IBEX) mission has shown that
variations in the ENA flux from the outer heliosphere are associated
with the solar cycle and longer-term variations in the solar wind. In
particular, there is a good correlation between the dynamic pressure of
the outbound solar wind and variations in the later-observed IBEX ENA
flux. The time difference between observations of the outbound solar
wind 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 apply 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 dHP is slightly south of the nose
direction (dHP ~ 110 – 120 au), with a
flaring toward the flanks and poles (dHP
~ 160 – 180 au). The heliosphere extends at least
~350 au tailward, which is the distance limit of the
technique.