SAN FRANCISCO -- Vivideruptions of the Northern Lights raced through Earth's atmosphere earlier thisyear, breaking speed and energy expectations.
A newNASA spacecraft caught the show, called an aurora, and has shed light onthe source of the magnetic storm's energy.
On March23, an auroral substorm erupted over Alaska and Canada and produced spectacularauroras for more than two hours, caught on camera by NASA?s THEMISsatellite. These THEMIS? observations were presented here today at a meeting ofthe American Geophysical Union.
?Theauroras surged westward twice as fast as anyone thought possible, crossing 15degrees of longitude in less than one minute,? said mission scientist VassilisAngelopoulos. ?The storm traversed an entire polar time zone, or 400 miles, in60 seconds flat.?
Thesatellite observed the substorm's development and witnessed small staccatoexplosions within the storm that each lasted about 10 minutes. Some of theoutbursts died out, while others went on to become major auroral events.
The powerof the storm blew scientists away; they estimate the total energy of thetwo-hour event at five hundred thousand billion Joules, or the energy of one5.5-magnitude earthquake.
The THEMISobservations also shed light on just where the substorms get their tremendousenergy.
?Thesatellites have found evidence of magnetic ropes connecting Earth?s upperatmosphere directly to the sun,? said David Sibeck of NASA?s Goddard Space Flight Center in Maryland. ?We believe that solar windparticles flow in along these ropes, providing energy for geomagnetic stormsand auroras.?
Spacecrafthave detected hints of magnetic ropes (essentially twisted bundles of magneticfields) before, but THEMIS provided the first 3-D look at a ropes' structure.
?THEMISencountered its first magnetic rope on May 20,? said Sibeck. ?It was verylarge, about as wide as Earth, and located approximately 40,000 miles (70,000kilometers) above Earth?s surface in a region called the magnetosphere.?
(Themagnetosphere is where the solar wind slams into Earth?s magnetic field.)
Theexplosions detected in the substorm happened ?where the solar wind first feelsthe effects of Earth?s magnetic field,? Sibeck said. ?Sometimes a burst ofelectrical current within the solar wind will hit the bow shock and--Bang! Weget an explosion.?
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