Exploring the Unseen: Extra-Heliospheric ENAs Observations on an Interstellar Probe

An observer inside the solar-wind bubble of the heliosphere is immersed in a cloud of the relatively dense plasma of the solar wind. Weak ENAs fluxes (extra-heliospheric ENA) generated on large distances outside the heliopause from whatever sources get stripped and/or photoionized while traveling in the Local Interstellar Medium (LISM) and then inside the inner heliosphere. Moreover, for an observer inside the heliosphere extra-heliopsheric ENA emissions, if any, may not be distinguishable from the heliospheric ENAs produced at the heliospheric interface. Being inside the heliopshere we are effective blind for extra-heliospheric ENA but what is out there? Outside the heliosphere hydrogen ENAs propagate distances of 500 - 1000 au before charge-exchanging to protons. An interstellar probe equipped with a proper ENA instrumentation and traveling distances up to 1000 au would be the only mean to investigate these extra-heliospheric ENA emissions. Deep sky ENA survey outside the heliopshere could be a highly exploratory science objective for such a mission. We also speculate on possible ENA sources apart from the heliosphere itself, for example, inhomogeneities of proton plasmas (not detectable in Lyman-alfa) present in LISM.