Parallax Measurements of the Ribbon of ENA Emission, Current Results and Future Prospects

Most theories for the bright ribbon of ENAs seen by IBEX (McComas et al., 2009, doi:10.1126/science.1180906) place the ribbon near the heliopause boundary between the solar wind and the interstellar medium, a distance of roughly 150 AU. Because IBEX collects ENAs from the same "slice" of sky every six months, astronomical parallax can be used to try to determine the distance to the ribbon in a completely model-independent way. This is complicated because the ribbon is a diffuse structure and there are statistical and temporal variations in the ENA intensities. A lower limit for the distance to the IBEX ENA Ribbon with the first ten maps will be presented. More years of IBEX maps will continue to refine the distance. But to really distinguish between competing theories, the increased sensitivity and resolution of the Interstellar Mapping and Acceleration Probe (IMAP) will be needed. Estimates of the parallax measuring capability of IMAP will also be presented.