NASA satellites discover what powers Northern Lights (8/10/2008)

When two or more magnetic field lines reconnect, energy is released back to Earth in the form of light â€" the Northern Lights.

The first time Ian Mann got a good look at the Northern Lights, he was driving north of Edmonton. A long way from his native England.

"We just pulled the truck over, cut the headlights and got out to look at the sky," said Mann, a physics professor at the University of Alberta and Canada Research Chair in Space Science. "In my opinion, it's one of the most beautiful things in nature."

Mann is one of a group of researchers who, using a fleet of five NASA satellites, have discovered that an explosion of magnetic energy a third of the way to the moon powers the Northern Lights.

The culprit is "magnetic reconnection," a common process that occurs when stressed magnetic field lines suddenly snap to a new shape, like a rubber band that's been stretched too far. Explosions on the sun's surface cause solar winds that hit the Earth, stretching the planet's magnetic field almost into the shape of a comet's tail. When two or more of those field lines touch, much of the energy is released into space, but some returns to Earth in the form of light, a process referred to as substorms.

"There have been two theories about the origins of the Northern Lights that have been hotly debated for about the last 30 years or so," said Mann. "One theory is that the phenomenon starts relatively close to Earth, and the other is that it happens further away. This is the first time ever that we've been able to see it happen, cradle to grave, so to speak."

While the results of this recent mission suggest that the magnetic reconnection happens further away from the Earth's surface, Mann said the debate will continue. "It's only one event that we've tracked so far, but NASA is extremely happy with how this mission has turned out and has extended the project, so we'll be able to take another look."

The mission, called Time History of Events and Macroscale Interactions during Substorms, used five satellites and a network of 20 ground observatories located throughout Canada and Alaska to observe the event. Launched on February 17, 2007, the identical satellites line up once every four days over the observatories and within Earth's magnetotail-the part of the magnetosphere facing away from the sun-at distances up to 15 times Earth's diameter. With each alignment, the satellites capture data that allow scientists to precisely pinpoint where, when, and how substorms develop.

Aside from being one of the world's most northern research universities, the U of A has a long history of tracking space weather phenomena, says Mann.

"Canada is the most accessible places anywhere on the planet for studying the Northern Lights," he said. "The physics department and the University of Albert have been working on understanding space weather, if you will, and the dynamics of the space environment where satellites fly, and the processes that create the Northern Lights for a number of decades."

The findings appeared online in Science Express and will be in print August 14 in the journal Science.

Note: This story has been adapted from a news release issued by the University of Alberta

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