Interaction of a neutral particle environment is much more complex. First, it can give your e-ion of the solar wind (the effect of exchange), and secondly there may be up to the Sun, where it will affect the force of gravity and light pressure.
The first effect leads to a drastic reduction in the size of the heliosphere and in stark contrast to how researchers can expect observed Voyager 1 and Voyager-2 ". Also, it changes the picture of the heliosphere in the tail (which moves Pioneer-10 "), a Mach disc, and tangential gap reflected shock waves. Unfortunately, to check the effects of earth observation is impossible and can only hope for measuring the spacecraft.
Those particles of interstellar medium, which had managed to penetrate into the interplanetary medium far more interesting from the standpoint of the observer. They not only can be seen, but also to obtain information about:
Conditions on the boundary of the heliosphere.
Many important details of chemistry interstellar medium.
Turbulence of the interstellar medium.
Physical conditions in the interstellar medium.