Plasma, not solid, liquid, or gas, is the most common state of matter in the universe.

On Earth, most of what we touch day to day is solid, liquid, or gas. But stars — including the Sun — are made of plasma, an ionized gas in which electrons have been stripped from atoms, leaving a mix of free-floating charged particles. Because stars make up the overwhelming majority of visible ordinary matter in the universe, plasma is by far its most common state.

Plasma also fills the vast, thin expanses of interstellar and interplanetary space, and shows up on Earth in lightning, neon signs, and the aurora. Its defining trait is that it responds strongly to electric and magnetic fields, behaving in ways solids, liquids, and gases don’t — which is part of why physicists treat it as a distinct fourth state of matter rather than just an unusual gas.