  Pickup ions are created when interstellar neutral atoms resonantly exchange
charge with the solar wind (SW) ions, especially in the supersonic part of the
wind, where they carry most of the plasma pressure. Here we present numerical
simulation results of the 3D heliospheric interface treating pickup ions as a
separate proton fluid. To satisfy the fundamental conservation laws, we solve
the system of equations describing the flow of the mixture of electrons,
thermal protons, and pickup ions. To find the density and pressure of pickup
ions behind the termination shock, we employ simple boundary conditions that
take into account the \emph{Voyager} observations that showed that the decrease
in the kinetic energy of the mixture at the termination shock predominantly
contributed to the increase in the pressure of pickup ions. We show that this
model adequately describes the flow of the plasma mixture and results in a
noticeable decrease in the heliosheath width.

Solar and Stellar Astrophysics;Space Physics