Aurora-Investigating Probes Set to Launch

Stefan Lovgren
for National Geographic News

January 18, 2007

A quintet of space probes will be launched next month to solve a decades-long mystery about auroras in Earth's atmosphere, NASA officials announced yesterday.

The probes will search for the origin of magnetic storms that cause auroras in the planet's Northern Hemisphere to change from slowly shimmering curtains of light into dancing streaks of briliant color.

(Photos: auroras, Earth's grand light show.)

Pinpointing when and where the storms originate will also enable researchers to better predict space weather.

In addition to lighting up the polar night, severe magnetic storms can disrupt spacecraft, radio communication, global positioning systems, and power transmission (related news: "Global Warming Could Disrupt GPS Satellites, Study Says" [November 29, 2006]).

The new mission "is a stepping stone toward understanding space weather phenomena that affect our lives," Vassilis Angelopoulos, principal investigator of the project at the University of California, Berkeley's Space Sciences Laboratory, told reporters yesterday.

Historic First

Charged particles emanating from the sun are the ultimate source of auroras.

When these particles pass near Earth, they flow around the planet's magnetic field lines.

But some of the particles leak into Earth's magnetosphere and collide with air molecules. The impact releases visible light, creating an aurora.

Sometimes a severe magnetic storm can cause energy to build up until Earth's magnetic field breaks. This releases a sudden burst of high-speed electrons—a geomagnetic substorm.

The substorm makes a normally green aurora ripple and turn red, purple, and white.

The five dishwasher-size probes, to be launched on February 15, will be looking for the places where substorms start.

The mission, dubbed Time History of Events and Macroscale Interactions during Substorms (THEMIS), marks the largest number of scientific satellites NASA has ever launched into orbit aboard a single rocket.

"Substorms start from a single point in space and within minutes progress past the moon's orbit, which is why we need multiple satellites," Angelopoulos said. "A single satellite cannot pinpoint the location."

The probes will orbit for about ten months before they assume their desired position in an arc over North America (see image at left).

From there the probes will map the continent's magnetic fields every four days. Angelopoulos expects that the orbiters will observe more than 30 substorms during the two-year mission.

"By taking the knowledge we gain from this discipline, we can develop the ability to both monitor and eventually forecast the effects of space weather throughout the solar system," said Jim Slavin, director of the Goddard Space Flight Center's heliophysics division in Greenbelt, Maryland.

Predicting space weather is important for keeping spacecraft and astronauts safe during a strong magnetic storm.

(Related news: "Space Weather Could Scrub Manned Mars Mission" [August 9, 2005].)

Accurate predictions could also help prevent disruption of communications and avoid power-line transmission failures on Earth's surface.

Studying space weather "has become more and more important," Angelopoulos said, "due to our increasing reliance on sophisticated space systems."

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