NASA THEMIS Spacecraft See Magnetic Reconnection

This animation shows the positions of the five THEMIS spacecraft, enabling them to observe the full process of magnetic reconnection and the resulting auroral substorm.

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Researchers from the THEMIS mission discovered that an explosion of magnetic energy a third of the way to the moon powers substorms, sudden brightenings and rapid movements of the aurora borealis, called the Northern Lights. Using five spacecraft in coordinated concentric orbits, researchers found evidence of magnetic reconnection, a common process that occurs throughout the universe when stressed magnetic field lines suddenly "snap" to a new shape, like a rubber band that's been stretched too far.

Substorms produce dynamic changes in the auroral displays seen near Earth's northern and southern magnetic poles, causing an especially energetic burst of light and movement in the Northern and Southern Lights. These changes transform auroral displays into auroral eruptions.

Substorms often accompany intense magnetic storms that can disrupt radio communications and global positioning system signals and cause power outages. Solving the mystery of where, when, and how substorms occur will allow scientists to construct more realistic substorm models and better predict a magnetic storm's intensity and effects.

These observations confirm for the first time that magnetic reconnection triggers the onset of substorms. The discovery supports the reconnection model of substorms, which asserts a substorm starting to occur follows a particular pattern. This pattern consists of a period of reconnection, followed by rapid auroral brightening and rapid expansion of the aurora toward the poles. This culminates in a redistribution of the electrical currents flowing in space around Earth.

CREDIT: NASA/GSFC SVS