Hi Nathan,
A solar storm can affect ALL the planets in our solar system...all the way out to Pluto and Neptune!
We know this because the two Voyager spacecraft are now out way beyond Pluto and Neptune...and they have instruments that can measure the effects of solar storms. The radio receivers on the Voyager spacecraft may have even picked up an echo from a solar storm hitting the big jump in density beyond 150 AU (150 times the distance from the Sun to Earth) where the solar wind meets the interstellar medium.
Paulett