Matter density in interplanetary space?

I was wondering, I have heard that space is a vaccuum, but is it totally
empty in the voids between the planets? The sun jettison matter during
solar flares, and there is such a thing as a solar wind. Does that
mean that matter like hydrogen or helium gas might be distributed in
interplanetary space? Or does the gavitational forces of the planets soak
all the gas up? It might be interesting to know if gas gas/dust clouds
form withing the solar system or if the stuff is even in distribution.

[[Mod. note -- The interstellar medium is quite nonuniform, but
a rough order-of-magnitude estimate for its density is a few atoms
per cubic centimeter (most hydrogen and helium). There is also a
significant amount of matter in dust grains, but I don't have
specific numbers handy. -- jt]]

Just curious,
RustyS