Energetic activity of the Heliosphere, showing 70-100 AU termination shock.

What is All this Space Within the Heliosphere Filled Up With?

Its composition was discovered to be filled with a combination of material, everything from gas, dust and plasma known as the solar wind. Plasma is defined as a heavily ionized form of matter somewhere between a gaseous and liquid state. Scientists have estimated that more than 99 percent of the matter in the universe exists in the plasma state. Plasma exists in and around the stars, including the sun, and throughout interstellar space. Most physicists classify it as the fourth state of matter.