U.S. scientists identify what powers Northern Lights

Using a fleet of five NASA satellites, U.S. scientists have identified the mechanism that triggers substorms in space and leads to the explosive release of energy that causes the spectacular brightening of the aurora borealis, or the Northern Lights, NASA reported Thursday.

File photo of the Northern Lights.Using a fleet of five NASA satellites, U.S. scientists have identified the mechanism that triggers substorms in space and leads to the explosive release of energy that causes the spectacular brightening of the aurora borealis, or the Northern Lights, NASA reported Thursday.

For 30 years, there have been two competing theories to explain the spectacular Northern Lights dancing.

One is that the trigger happens about one-sixth of the distance to the moon, when charged ions and electrons implode toward Earth as the space currents are disrupted.

A second theory says the trigger is farther out, about one-third of the distance to the moon. When two magnetic field lines come close together due to the storage of energy from the sun, a critical limit is reached and the magnetic field lines reconnect, causing magnetic energy to be transformed into kinetic energy and heat.

"Our data show clearly and for the first time that magnetic reconnection is the trigger," said Vassilis Angelopoulos, the principal investigator of the five-satellite THEMIS project." Reconnection results in a slingshot acceleration of waves and plasma along magnetic field lines, lighting up the aurora underneath even before the near-Earth space has had a chance to respond."

Previous studies of the Earth's magnetosphere and space weather have been unable to pinpoint the origin of substorms, which are large magnetic disturbances.

"We need to understand this environment and eventually be able to predict when these large energy releases will happen so astronauts can go inside their spacecraft and we can turn off critical systems on satellites so they will not be damaged," Angelopoulos said. "This has been exceedingly difficult in the past, because previous missions, which measured the plasma at one location, were unable to determine the origin of the large space storms."

THEMIS stands for Time History of Events and Macroscale Interactions during Substorms mission. Launched on Feb. 17, 2007, THEMIS is expected to observe approximately 30 substorms in its nominal lifetime.