NASA Spacecraft Make New Discoveries About Northern Lights
A fleet of NASA spacecraft, launched less than eight months
ago, has made three important discoveries about spectacular eruptions of
Northern Lights called "substorms" and the source of their power.
NASA's Time History of Events and Macroscale Interactions during Substorms
(THEMIS) mission observed the dynamics of a rapidly developing substorm,
confirmed the existence of giant magnetic ropes and witnessed small explosions
in the outskirts of Earth's magnetic field. The findings will be presented at
the annual meeting of the American Geophysical Union in San Francisco in
December.
The discoveries began on March 23, when a substorm erupted over Alaska and
Canada, producing vivid auroras for more than two hours. A network of ground
cameras organized to support THEMIS photographed the display from below while
the satellites measured particles and fields from above.
“The substorm behaved quite unexpectedly," says Vassilis Angelopoulos, the
mission's principal investigator at the University of California, Los Angeles.
"The auroras surged westward twice as fast as anyone thought possible, crossing
15 degrees of longitude in less than one minute. The storm traversed an entire
polar time zone, or 400 miles, in 60 seconds flat.”
Photographs taken by ground cameras and NASA's Polar satellite (also supporting
the THEMIS mission) revealed a series of staccato outbursts each lasting about
10 minutes. Angelopoulos said that some of the bursts died out while others
reinforced each other and went on to become major onsets.
Angelopoulos was quite impressed with the substorm's power and he estimated the
total energy of the two-hour event at five hundred thousand billion Joules.
That's equivalent to the energy of one magnitude 5.5 earthquake . Where does
all that energy come from? THEMIS may have found the answer.
"The satellites have found evidence of magnetic ropes connecting Earth's upper
atmosphere directly to the sun," said David Sibeck, project scientist for the
mission at NASA's Goddard Space Flight Center, Greenbelt, Md. "We believe that
solar wind particles flow in along these ropes, providing energy for
geomagnetic storms and auroras."
A magnetic rope is a twisted bundle of magnetic fields organized much like the
twisted hemp of a mariner's rope. Spacecraft have detected hints of these ropes
before, but a single spacecraft was insufficient to map their 3D structure.
THEMIS' five identical micro-satellites were able to perform the feat.
"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 km) above Earth's surface in a region called the magnetopause." The
magnetopause is where the solar wind and Earth's magnetic field meet and push
against one another like sumo wrestlers locked in combat. There, the rope
formed and unraveled in just a few minutes, providing a brief but significant
conduit for solar wind energy.
THEMIS also has observed a number of small explosions in Earth's magnetic bow
shock. "The bow shock is like the bow wave in front of a boat," explained
Sibeck. "It is where the solar wind first feels the effects of Earth's magnetic
field. Sometimes a burst of electrical current within the solar wind will hit
the bow shock and—Bang! We get an explosion."
The THEMIS satellites are equipped with instruments that measure ions,
electrons and electromagnetic radiation in space. The satellites will line up
along the sun-Earth line next February to perform their key measurements.
Researchers expect to observe, for the first time, the origin of substorm
onsets in space and learn more about their evolution. Scientists from the US,
Canada, Western Europe, Russia and Japan are contributing to the scientific
investigation over the next two years.
THEMIS is the fifth medium-class mission under NASA's Explorer Program, which
provides frequent flight opportunities for world-class scientific
investigations within the heliophysics and astrophysics science areas.
The Explorer Program Office at Goddard manages the NASA-funded THEMIS mission.
The University of California, Berkeley's Space Sciences Laboratory is
responsible for project management, science and ground-based instruments,
mission integration and post launch operations. ATK (formerly Swales
Aerospace), Beltsville, Md., built the THEMIS probes.
Related Links:
> THEMIS site
Cynthia O'Carroll
Goddard Space Flight Center