On February 17, 2007, NASA launched a quintet of satellites to figure out the science behind Earth's most colorful auroras. [‘On This Day in Space’ Video Series on Space.com](https://www.space.com/39251-on-this-day-in-space.html)

The mission was titled THEMIS, which stands for Time History of Events and Macroscale Interactions during Substorms. Substorms happen when Earth's magnetosphere is disrupted by solar wind, or energetic particles flowing from the sun. This causes auroras to brighten and undulate in the sky. THEMIS helped scientists understand what triggers these substorms. All five THEMIS satellites launched on the same Delta II rocket before splitting up to orbit Earth in formation.