Scientists think they have discovered the energy source of the spectacular color displays seen in the northern lights.
New data from NASA's Themis mission, a quintet of satellites launched this winter, found the energy comes from a stream of charged particles from the sun flowing like a current through twisted bundles of magnetic fields connecting Earth's upper atmosphere to the sun.
The energy is then abruptly released in the form of a shimmering display of lights visible in the upper latitudes of the Northern Hemisphere, said principal investigator Vassilis Angelopoulos of the University of California, Los Angeles.
Results were presented Tuesday at the American Geophysical Union meeting.
In March, the satellites detected a burst of northern lights, or auroras borealis, over Alaska and Canada. During the two-hour light show, the satellites measured particle flow and magnetic fields from space.
To scientists' surprise, the geomagnetic storm powering the auroras raced 400 miles in a minute across the sky. Angelopoulos estimated the storm's power was equal to the energy released by a magnitude 5.5 earthquake.
"Nature was very kind to us," Angelopoulos said.
Although researchers have suspected the existence of wound-up bundles of magnetic fields that provide energy for the auroras, the phenomenon was not confirmed until May, when the satellites became the first to map their structure some 40,000 miles above the Earth's surface.
Scientists hope the satellites will record a geomagnetic storm next year that's now in the making, and end the debate about when the storms are triggered.