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WASHINGTON (Reuters) - The multicolored aurora borealis and aurora australis -- the Northern Lights and Southern Lights -- represent some of Earth's most dazzling natural displays.
Now scientists using data from five NASA satellites have learned what causes frequent auroral flare-ups that make this green, red and purple lightshow that shimmers above Earth's northernmost and southernmost regions even more spectacular.
Writing in the journal Science, the scientists said on Thursday that explosions of magnetic energy occurring a third of the way between Earth and the moon drive the sudden brightening of the Northern Lights and Southern Lights.
There had been debate among scientists dating back decades about what triggers these auroral flare-ups.
The findings from the THEMIS satellites and a network of 20 ground observatories in Canada and Alaska confirmed that it is due to a process called "magnetic reconnection." THEMIS stands for Time History of Events and Macroscale Interactions during Substorms mission.
Auroral displays are associated with the solar wind -- electrically charged particles continuously spewing outward from the sun. Earth's magnetic field lines reach far out into space as they store energy from the solar wind.
The researchers said that as two magnetic field lines come close together due to the storage of energy from the sun, a critical limit is reached and the lines reconnect, causing magnetic energy to be turned into kinetic energy and heat. The release of this energy sparks the auroral flare-ups.
"We showed that the process begins far from Earth first and propagates Earthward later," said Vassilis Angelopoulos of the University of California at Los Angeles, who led the research.
The moon is located about 240,000 miles from Earth, and this process is occurring roughly 80,000 miles from Earth.
The same mechanism causing the auroral brightening also can cause problems for satellites, power grids and communications systems on Earth and could endanger astronauts in space, the researchers said.
Editing by Julie Steenhuysen and Philip Barbara