Would not the gravity of the solar system of pulled in much of the mass and what would be interesting is a probe sent directly up and down. Is this change in density a flat bubble of spherical, as in is the effect greater along the plane of the solar system.<p>That would provide the data to help nail this. Equally, what effect will this have upon the amount of matter in the universe and the hunt for dark matter/energy.<p>But logically, the gravity effect given the time of the universe, it is plausible that would be clustering (solar systems) and in-between those the viability of more matter in space and as such, density becomes plausible - so may explain what we are seeing here. Now what I'll be interested in is will the Voyager probes speed up, slow down or no change. The extra density will in theory slow them down, equally the weaker effects of gravity from the solar system would become less of a factor - might be they balance out for a period and may of already seen this. Still, value for money - Voyager is the gift that keeps on giving.<p>Now here is a thought, will the mass of the voyager probe in an environment in which it is the the most influential gravity start to build up these space particles. If that is so, who know's, the probes may well go on to attract enough mass that over billions and billions of years go onto form their own solar systems. Now that would be mind blown.