Plasma is found almost everywhere you look, from the stars overhead to the blood in your veins. The word “plasma” refers to two very different things: the fourth state of matter (an electrically charged gas) and the liquid component of blood. As a state of matter, plasma makes up an estimated 99.9% of the visible universe. On Earth, it shows up in lightning bolts, neon signs, and the upper atmosphere. Blood plasma, meanwhile, circulates through every human body. Here’s where each type exists and what it does.
Stars and the Sun
Nearly all the matter you can see in space is plasma. Stars, including our sun, are giant balls of it. Inside a star’s core, temperatures and pressures are so extreme that atoms are stripped of their electrons, creating a superheated soup of charged particles. The sun’s outer atmosphere, called the corona, reaches temperatures around 750,000 to over 1.1 million degrees Kelvin. Even at those extreme temperatures, the corona is surprisingly thin, with particle densities of roughly 13 million to 70 million electrons per cubic centimeter depending on the region. That’s far less dense than the air you breathe, but it’s still enough plasma to drive the solar wind that streams outward across the entire solar system.
Interstellar Space
Plasma doesn’t stop at the edge of the solar system. The space between stars, known as the interstellar medium, contains a thin but measurable plasma. NASA’s Voyager 1 and Voyager 2 spacecraft have been directly measuring this plasma since crossing the boundary where the sun’s influence ends. Their instruments show that the electron density in the nearby interstellar medium gradually increases with distance, reaching about 0.12 electrons per cubic centimeter at 160 astronomical units from the sun. That’s incredibly sparse, but spread across the vast distances between stars, it adds up to an enormous amount of matter.
Earth’s Upper Atmosphere
You don’t need to leave the planet to find plasma. The ionosphere, a layer of Earth’s atmosphere stretching roughly 50 to 400 miles above the surface, is filled with it. Solar radiation strips electrons from gas molecules at those altitudes, creating layers of plasma that shift in density between day and night. This plasma is the reason shortwave radio signals can bounce around the globe, and it’s also why solar storms can disrupt GPS signals, satellite communications, and power grids on the ground. Changes in the ionosphere’s density and composition directly affect how reliably those signals travel.
Higher still, the Van Allen radiation belts trap energetic charged particles in doughnut-shaped zones around the planet. These belts contain electrons with energies reaching 10 megaelectron volts or more, accelerated by interactions with electromagnetic waves. The outer belt is dynamic, swelling and shrinking in response to solar activity, while the inner belt remains relatively stable.
Lightning
Lightning is one of the most dramatic examples of plasma on Earth’s surface. During a strike, the electrical discharge heats the surrounding air so rapidly that it ionizes, creating a channel of plasma with electron temperatures around 23,000 Kelvin. That’s roughly four times hotter than the surface of the sun. The plasma channel exists only for a fraction of a second, but it carries enormous energy, which is why lightning can melt sand, split trees, and generate the shockwave we hear as thunder.
Everyday Technology
Plasma is working in more places around your home and workplace than you might expect. Neon signs glow because an electrical current passes through a sealed tube of low-pressure gas, stripping electrons from the neon atoms and creating plasma. The specific gas inside determines the color: neon produces red-orange, argon gives off blue-violet, and other noble gases or gas mixtures create different hues. Fluorescent light bulbs work on the same principle, using mercury vapor plasma to generate ultraviolet light that then excites a phosphor coating on the inside of the tube.
Plasma televisions (now largely replaced by LED and OLED screens) contained millions of tiny cells filled with noble gases. Each cell was essentially a miniature neon sign, with the gas ionized by electrical signals to produce light. Plasma also plays a role in industrial settings. Plasma cutters use an electric arc to ionize gases like nitrogen or argon mixtures, creating a jet of plasma hot enough to slice through steel and other metals with precision.
Blood Plasma in the Human Body
The other kind of plasma is biological. Blood plasma is the pale yellow liquid that carries red blood cells, white blood cells, and platelets through your circulatory system. It accounts for about 60% of your total blood volume, with the remaining 40% made up of cells. Plasma is roughly 90% water, with the rest consisting of proteins, electrolytes, hormones, and waste products. It plays a central role in maintaining blood pressure, regulating body temperature, and transporting nutrients and immune molecules throughout the body.
Plasma can be donated separately from whole blood through a process called plasmapheresis, where blood is drawn, the plasma is separated out, and the remaining blood cells are returned to the donor. The American Red Cross accepts plasma donations from healthy individuals who are at least 17 years old and weigh at least 110 pounds. Donors with type AB blood are especially sought after because AB plasma can be given to patients of any blood type. Eligible donors can give plasma every 28 days, up to 13 times per year. Donated plasma is used to treat burn victims, people with clotting disorders, and patients undergoing major surgeries.
Why Plasma Is So Common
Plasma forms whenever enough energy is applied to a gas to knock electrons free from their atoms. On Earth, where temperatures and pressures keep most matter in solid, liquid, or gas form, plasma requires special conditions like electrical discharges or extreme heat. But Earth is the exception. Most of the universe is hot enough, or exposed to enough radiation, that plasma is the default state of matter. Every star, every nebula, and most of the thin gas filling the spaces between them exists as plasma. The fact that we live on a cool, dense planet surrounded by neutral gases is what makes plasma seem rare, when it’s actually the most common form of ordinary matter in existence.