A perfect vacuum doesn't exist anywhere in the universe. Instead, space is blasted by a 1.5-million-mph storm of plasma because the Sun literally cannot hold onto its own atmosphere.
To understand how space can be both a vacuum and filled with a solar storm, you first have to look at gravity. It acts as a cosmic broom. Over billions of years, it pulled scattered gas and dust together, clumping it into dense bodies like stars and planets. Because the universe is so vast, pulling matter into these compact spheres leaves the expanses between them nearly empty. At sea level on Earth, a single cubic centimeter of air contains roughly 25 quintillion molecules. In interstellar space, that same volume might contain just one or two hydrogen atoms.
Within our solar system, that space is filled with a continuous stream of charged particles moving at supersonic speeds: the solar wind.
To understand the solar wind, you have to look at the Sun’s outer atmosphere, the corona. During a total solar eclipse, when the moon blocks the Sun's blinding surface, you can see this atmosphere.
The surface of the Sun is about 5,500 °C (10,000 °F). Counterintuitively, as you move away from the surface into the corona, the temperature skyrockets to over 1,000,000 °C. The exact mechanics of this extreme heating are still studied, but it is driven by the Sun's churning magnetic fields releasing immense energy into the atmosphere.
At these million-degree temperatures, gases cannot remain stable. They are ripped apart into plasma, a highly energetic soup of freely moving electrons and protons. Because this plasma is so hot, its particles move fast enough to overcome the Sun's immense gravitational pull.
This material constantly boils off into space, expanding outward in all directions. It is accelerated by shifting magnetic fields, hurtling outward at hundreds of miles per second. This stream of particles blows past Earth and fills our entire solar system, forming a protective bubble of charged particles called the heliosphere.
