Kepler in the 1600's theorized it - of course it was not possible to actually measure particles until we had satellites able to do so.
Voyager 2 showed that the voyager wind extends past Pluto and probably a lot further. But all we *know* for sure is the Voyager data.
I'd prefer not to try to attach a solar sail to an asteroid. I don't know exactly, but the acceleration is very low - but it can continue for a long time, allowing you to build up pretty good velocity before it is effectively unusable.