IBEX and Voyager observations require a heliosheath between ~122 and 143 AU that requires that Voyager 1 is not yet in interstellar space

Abstract:

We have disputed the general assumption that Voyager 1 (V1) is exploring the local interstellar medium, arguing that the high density measured at ~122 AU is not that of interstellar thermal protons, but rather of compressed solar wind. This conclusion is supported by V1 measurements of the magnetic field direction (which remained essentially unchanged) and decreasing solar wind flow speed. Here we show that only the Fisk & Gloeckler (F&G) model for the nose region of the heliosheath can explain the lowest energy portion of the Energetic Neutral Hydrogen (ENH) differential intensity spectra observed by IBEX in the look directions aimed at V1 and V2, respectively. The F&G model provides the simplest explanation for the intensity and spectral shape of 0.006 to 4 keV ENH whose source is not only heliosheath pickup protons but, most importantly, the compressed solar wind which creates nearly all of the < ~0.5 keV ENH. IBEX ENH spectra provide crucial information on the evolution with radial distance of distribution functions of solar wind, pickup and suprathermal tail protons, allowing us to compute radial profiles of the density and pressure of each of these particle populations. Furthermore, low-energy ENH measurements require the uncoupling of the two heliospheric gases (solar wind and the mobile pickup, tails and ACRs protons) of the F&G model, and allow us to compute the radial and speed dependence of the uncoupling and escape probability functions for mobile particles.