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It is well known that the Solar System is presently moving through apartially ionized local interstellar medium. This gives rise to a counter-flowsituation requiring a consistent description of behaviour of the two fluids --ions and neutral atoms -- which are dynamically coupled by mutual chargeexchange processes. Solutions to this problem have been offered in theliterature, all relying on the assumption that the proton fluid, even underevidently nonequilibrium conditions, can be expected to stay in ahighly-relaxated distribution function given by mono-Maxwellians shifted by thelocal proton bulk velocity. Here we check the validity of this assumption,calculating on the basis of a Boltzmann-kinetic approach the actually occurringdeviations. As we show, especially for low degrees of ionization, $\xi \le0.3$, both the H-atoms and protons involved do generate in the heliosphericinterface clearly pronounced deviations from shifted Maxwellians withasymmetrically shaped distribution functions giving rise to non-convectivetransport processes and heat conduction flows. Also in the inner heliosheathregion and in the heliotail deviations of the proton distribution from thehydrodynamic one must be expected. This sheds new light on the correctness ofcurrent calculations of H-atom distribution functions prevailing in the innerheliosphere and also of the Lyman-$\alpha $ absorption features in stellarspectra due to the presence of the hydrogen wall atoms. Deviations fromLTE-functions would be even more pronounced in magnetic interfaces, which viaCGL-effects cause temperature anisotropies to arise.Comment: 18 pages, 8 figures, A&A in pres

A kinetic control of the heliospheric interface hydrodynamics of charge-exchanging fluids