You probably learned in school about the three states of matter: solids, liquids and gases. For example, H2O can be frozen into solid ice, it can be liquid water or it can evaporate to form a gas. But there is a fourth state of matter -- plasma -- and it's the most common form of matter in the universe. Plasma is formed by superheating a gas. When this happens, the electrons break free of the atoms and become free-floating, and the gas becomes positively charged (ionized). This mix of ionized gas and free-floating electrons makes up plasma. The sun and other stars are made of plasma, while it's not too common on Earth, where solids, liquids and gas rule the day.
Have SETI scientists ever thought they made contact?
Answered by Jill Tarter
Why shadows on moon-landing photos are different lengths?
Answered by Discovery Channel
How do NASA and Hubble communicate with each other?
Answered by Science Channel