The Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission was originally a constellation of five NASA satellites (THEMIS A through THEMIS E) to study energy releases from Earth's magnetosphere known as substorms, magnetic phenomena that intensify auroras near Earth's poles. The name of the mission is an acronym  alluding to the Titan, Themis.

Themis (Greek: Θέμις) is an ancient Greek Titaness. She is described as "of good counsel", and is the personification of divine order, law, natural law and custom. Themis means "divine law" rather than human ordinance, literally "that which is put in place", from the Greek verb títhēmi (), meaning "to put".