Energy Source of Northern Lights Found

Anne Minard in San Francisco, California

NASA spacecraft have revealed new insights into the forces that cause the northern lights, including giant magnetic “ropes” between Earth and the sun.

Until now, scientists haven’t had adequate tools to study how energy from the sun is captured by Earth’s magnetic field to trigger the awe-inspiring phenomenon.

“What it shows is promise,” said Vassilis Angelopoulos, researcher at the University of California at Los Angeles and principal investigator for a new NASA mission to study auroras.

“We’re coming up on a new era in space physics.”

The findings were presented at a teleconference today at the fall meeting of the American Geophysical Union in San Francisco.

Perfect Storm

The latest discoveries began on March 23, when a “substorm” erupted over Alaska and Canada, producing vivid auroras for more than two hours. During such an event, the northern lights’ green and white streaks periodically build in intensity until they blast apart into multicolored, fragmented lights.

(Download a desktop photo of the northern lights.)

A network of ground cameras photographed the display from below while a series of five satellites, collectively called THEMIS, looked on from above.

(Read about the THEMIS mission and the probes’ launch earlier this year.)

“The auroras surged westward twice as fast as anyone thought possible, crossing 15 degrees of longitude in less than one minute,” Angelopoulos said.

“The storm traversed an entire polar time zone, or 400 miles [640 kilometers], in 60 seconds flat.”

The images revealed a series of staccato outbursts each lasting about ten minutes. Some of the bursts died out, while others reinforced each other.

The researchers likened the substorm’s power to a magnitude 5.5 earthquake.

Magnetic “Ropes”

NASA’s THEMIS probes are designed to unravel the mysterious dynamics that create such colorful displays.

Angelopoulos said the prime observation season for the northern lights hasn’t begun yet, but already the results are exciting.

“The satellites have found evidence of magnetic ‘ropes’ connecting Earth’s upper atmosphere directly to the sun,” said David Sibeck, project scientist for the mission at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

These ropes could serve as conduits for waves of charged particles from the sun called solar wind.

“We believe that solar wind particles flow in along these ropes, providing energy for geomagnetic storms and auroras.”

Spacecraft have detected hints of these ropes before, but a single spacecraft was insufficient to map their 3-D structure.

THEMIS’ identical micro-satellites were able to perform the feat.

The satellites have also glimpsed the evolution of heat waves and pressure blasts emitted from the northern lights’ substorm.

Angelopoulos likened THEMIS’ role to that of weather stations in our ability to predict atmospheric weather a century ago.

“These substorm processes are really helping us to understand and predict space weather,” Angelopoulos said.