Northern Lights Race Across the Sky

SAN FRANCISCO -- Vivid eruptions of the Northern Lights raced through Earth's atmosphere earlier this year, breaking speed and energy expectations.

A new NASA spacecraft caught the show, called an aurora, and has shed light on the source of the magnetic storm's energy.

On March 23, an auroral substorm erupted over Alaska and Canada and produced spectacular auroras for more than two hours, caught on camera by NASA?s THEMIS satellite. These THEMIS? observations were presented here today at a meeting of the American Geophysical Union.

?The auroras surged westward twice as fast as anyone thought possible, crossing 15 degrees of longitude in less than one minute,? said mission scientist Vassilis Angelopoulos. ?The storm traversed an entire polar time zone, or 400 miles, in 60 seconds flat.?

The satellite observed the substorm's development and witnessed small staccato explosions within the storm that each lasted about 10 minutes. Some of the outbursts died out, while others went on to become major auroral events.

The power of the storm blew scientists away; they estimate the total energy of the two-hour event at five hundred thousand billion Joules, or the energy of one 5.5-magnitude earthquake.

The THEMIS observations also shed light on just where the substorms get their tremendous energy.

?The satellites have found evidence of magnetic ropes connecting Earth?s upper atmosphere directly to the sun,? said David Sibeck of NASA?s Goddard Space Flight Center in Maryland. ?We believe that solar wind particles flow in along these ropes, providing energy for geomagnetic storms and auroras.?

Spacecraft have detected hints of magnetic ropes (essentially twisted bundles of magnetic fields) before, but THEMIS provided the first 3-D look at a ropes' structure.

?THEMIS encountered its first magnetic rope on May 20,? said Sibeck. ?It was very large, about as wide as Earth, and located approximately 40,000 miles (70,000 kilometers) above Earth?s surface in a region called the magnetosphere.?

(The magnetosphere is where the solar wind slams into Earth?s magnetic field.)

The explosions detected in the substorm happened ?where the solar wind first feels the effects of Earth?s magnetic field,? Sibeck said. ?Sometimes a burst of electrical current within the solar wind will hit the bow shock and--Bang! We get an explosion.?

• VIDEO: The THEMIS Aurora Mission Revealed
• VIDEO: THEMIS Away! Spacecraft Quintet Begin Aurora Hunt
• All About Auroras