Scientists solve 30-year-old aurora borealis mystery

UCLA space scientists and colleagues have identified the mechanism that triggers substorms in space; wreaks havoc on satellites, power grids and communications systems; and leads to the explosive release of energy that causes the spectacular brightening of the aurora borealis, also known as the northern lights.

For 30 years, there have been two competing theories to explain the onset of these substorms, which are energy releases in the Earth's magnetosphere, said Vassilis Angelopoulos, a UCLA professor of Earth and space sciences and principal investigator of the NASA-funded mission known as THEMIS (Time History of Events and Macroscale Interactions during Substorms).

One theory is that the trigger happens relatively close to Earth, about one-sixth of the distance to the moon. According to this theory, large currents building up in the space environment, which is composed of charged ions and electrons, or "plasma," are suddenly released by an explosive instability. The plasma implodes toward Earth as the space currents are disrupted, which is the start of the substorm.

A second theory says the trigger is farther out, about one-third of the distance to the moon, and involves a different process: When two magnetic field lines come close together due to the storage of energy from the sun, a critical limit is reached and the magnetic field lines reconnect, causing magnetic energy to be transformed into kinetic energy and heat. Energy is released, and the plasma is accelerated, producing accelerated electrons.

Which theory is right?

"Our data show clearly and for the first time that magnetic reconnection is the trigger," said Angelopoulos, who reports the research in the July 24 online issue of the journal Science. "Reconnection results in a slingshot acceleration of waves and plasma along magnetic field lines, lighting up the aurora underneath even before the near-Earth space has had a chance to respond. We are providing the evidence that this is happening."

Previous studies of the Earth's magnetosphere and space weather have been unable to pinpoint the origin of substorms, which are large magnetic disturbances. Ionized gas emitted from the sun's surface speeds up as it moves away from the sun, attaining speeds of 1 million mph and interacting with the Earth's upper atmosphere, which is also ionized, Angelopoulos said. Substorms are building blocks of larger storms.

"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. "This has been exceedingly difficult in the past, because previous missions, which measured the plasma at one location, were unable to determine the origin of the large space storms. To resolve this question properly requires correlations and signal-timing at multiple locations. This is precisely what was missing until now."

At high northern latitudes in the northern U.S. and Canada, shimmering bands of light called the aurora borealis, or northern lights, stretch across the sky from the east to the west. During the geomagnetically disturbed periods known as substorms, these bands of light brighten. These multicolored light shows are generated when showers of high-speed electrons descend along magnetic field lines to strike the Earth's upper atmosphere. Scientists want to learn when, where and why solar wind energy stored within the Earth's magnetosphere is explosively released to accelerate these electrons.

THEMIS is establishing for the first time when and where substorms begin, determining how the individual components of substorms interact, and discovering how substorms power the aurora borealis.

"We discovered what sparks the magnificent light show of the aurora," Angelopoulos said.

THEMIS has five satellites — with electric, magnetic, ion and electron detectors — in carefully chosen orbits around the Earth and an array of 20 ground observatories with automated, all-sky cameras located in the northern U.S. and Canada that catch substorms as they happen. The ground observatories take images of the aurora in white light. One satellite is a third of the distance to the moon, one is about a fourth of the distance and three are about a sixth of the distance. The outermost satellite takes four days to orbit the Earth, the next one two days, and the closest ones orbit the Earth in just one day. Every four days, the satellites line up.

As the satellites are measuring the magnetic and electric fields of the plasma above the Earth's atmosphere once every four days, the ground-based observatories are imaging the auroral lights and the electrical currents from space that generate them.

THEMIS was launched on Feb. 17, 2007, from Cape Canaveral, Fla., and is expected to observe approximately 30 substorms in its nominal lifetime.

"Armed with this knowledge, we are not only putting to rest age-old questions about the origin of the spectacular auroral eruptions but will also be able to provide statistics on substorm evolution and model its effects on space weather," Angelopoulos said.

Source: University of California - Los Angeles

Related stories:

NASA Satellites Discover What Powers Northern Lights
(PhysOrg.com) -- Researchers using a fleet of five NASA satellites have discovered that explosions of magnetic energy a third of the way to the moon power substorms that cause sudden brightenings and rapid movements of the aurora borealis, called the Northern Lights.
Space science simulation at UNH now better, faster, cheaper
Cashing in on the underlying technology that seamlessly renders graphics for state-of-the-art video games, space scientists at the University of New Hampshire have bundled together 40 PlayStation3 consoles to affordably simulate one of the "grand challenges" of modern computational science - the interaction between Earth's magnetic field or "magnetosphere" and the solar wind. Climate change is another supercomputing grand challenge.
Spring is Aurora Season
What are the signs of spring? They are as familiar as a blooming daffodil, a songbird at dawn, a surprising shaft of warmth from the afternoon sun. And, oh yes, don’t forget the aurora borealis. Spring is aurora season. For reasons not fully understood by scientists, the weeks around the vernal equinox are prone to Northern Lights. Canadians walking their dogs after dinner, Scandinavians popping out to the sauna, Alaskan Huskies on the Iditarod trail -- all they have to do is look up and behold, green curtains of light dancing across the night sky. Spring has arrived!
THEMIS probes view auroral substorms, bowshock explosions
Five satellites launched last February to probe magnetic storms around the Earth will move into prime observing position next month, but they already have produced important new information on the interactions between the solar wind and the Earth's magnetic field.
Scientists report first findings on key astrophysics problem
In a paper published recently in the journal Nature Physics, an international team of space scientists led by researchers from the University of New Hampshire present findings on the first experimental evidence that points in a new direction toward the solution of a longstanding, central problem of plasma astrophysics and space physics.
Cluster and double star uncover more on bright aurorae
Cluster data has helped provide scientists with a new view of magnetospheric processes, challenging existing theories about magnetic substorms that cause aurorae and perturbations in GPS signals.
Cluster sees tsunamis in space
Cluster is providing new insights into the working of a ‘space tsunami’ that plays a role in disrupting the calm and beautiful aurora, or northern lights, creating patterns of auroral dances in the sky.
THEMIS weighs in on the Northern Lights
Instruments known as solid-state telescopes (SSTs), built with detectors fabricated at Lawrence Berkeley National Laboratory and carried aboard the recently launched THEMIS mission, have delivered their first data on how charged particles in the solar wind interact with Earth's magnetic field to shape the planet's magnetosphere.

News discussion:

Space & Earth science news