A flotilla
of NASA probes has solved the 30-year mystery behind the most colorful aurora
displays on Earth and the explosive magnetic "substorms" that spawn
them.
NASA's five
THEMIS spacecraft in different orbits around Earth spotted the trigger for the substorms,
powerful energy bursts in the planet's magnetic field that can interfere with
satellites, power grids and supercharge
the aurora borealis, also known as the northern lights.
"We discovered what
sparks the magnificent light show of the aurora," said THEMIS principal
investigator Vassilis Angelopoulos, a space scientist at the University of
California, Los Angeles.
Angelopoulos and his team
used the THEMIS
probes to monitor the energy levels in Earth's magnetic field. In February
of this year, the spacecraft spotted substorms originating in the tail of the
magnetosphere that streams out away from the sun. As energy levels in the
magnetic field lines built up, they drew ever closer to one another until they
reconnected, setting off a storm, researchers said.
For the last three decades,
researchers were undecided on whether the substorms stemmed from magnetic field
lines reconnecting, or originated much closer to Earth where they were triggered
by explosive instability.
"Our data show clearly
and for the first time that magnetic reconnection is the trigger," said
Angelopoulos.
The research is detailed in
the July 24 online edition of the journal Science.
First
discovered in the 19th century, magnetic substorms are recurring energy bursts
stemming from the release of charged particles — collected from the sun's solar
wind — in the Earth's magnetic field. The high-energy particles zoom down the
Earth's magnetic field lines until they collide with the planet's upper
atmosphere to create dazzling,
shifting colors in the aurora borealis.
Researchers hope that by better
understanding the storms, they will be able to prepare for or predict major
space weather events before the cosmic tempests interfere with communications
or endanger astronauts
in Earth orbit.
"We need to understand
this environment and eventually be able to predict when these large energy
releases will happen so astronauts can go inside their spacecraft and we can
turn off critical systems on satellites so they will not be damaged,"
Angelopoulos said, adding that previous missions could only track bursts at a
single point and time. "To resolve this question properly requires correlations
and signal-timing at multiple locations. This is precisely what was missing
until now."
NASA's
$200 million THEMIS spacecraft, short for Time History of Events and
Macroscale Interactions During Substorms, launched in February 2007 on a
two-year mission to hunt for the substorm source. The five dishwasher-sized
spacecraft are arranged in different orbits between the Earth and moon, and are
working in conjunction with 20 ground-based observatories across the northern United
States and Canada to monitor substorm activity.
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