A proton is one of the tiny particles that make up the center, or nucleus, of an atom. Think of an atom like a miniature solar system: the nucleus sits at the center like the sun, and electrons orbit around it like planets. The nucleus contains protons and another type of particle called neutrons.

What makes protons special is their positive electrical charge. Electrons have a negative charge, and protons have a positive charge of exactly the same strength. In most atoms, the number of protons equals the number of electrons, so their charges balance out.

The number of protons in an atom determines what element it is. Hydrogen atoms have one proton, helium atoms have two, carbon atoms have six, and gold atoms have 79. Change the number of protons, and you've changed the element itself.

Protons are incredibly small and stable. The protons in your body have existed since the earliest moments of the universe, over 13 billion years ago. Scientists identified the proton in the early 1900s while experimenting with atoms, helping unlock the secrets of how matter works.