Re: Some surprising results (for the layman)
We have plasma streaming out from the Sun at some velocity. the density of the plasma is constantly reducing as it spreads out over a larger area. The momentum of the plasma and the pressure exerted by it is also reducing. If the heliopause represents the boundary where the pressure of interstellar plasma is equal to the solar wind, then unless the interstellar plasma is travelling toward the sun with the same or greater velocity (and lets face it it wont be unless we we closer to some other star), the only way you can have a point where the two pressures are equal and the combined momentum is zero, is if the interstellar medium is more dense. It has to be more dense because the solar wind is travelling at a greater velocity than the interstellar plasma. The solar wind is travelling at a greater velocity away from the Sun than the interstellar plasma is travelling towards the Sun because the solar wind it comes from a star close by, and by comparison the interstellar plasma is likely to be in thermal equilibrium, which will be cooler and thus also more dense than the solar wind, because it has been sitting in interstellar space for billions of years.