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Feature

Coronal mass ejection (CME) on sun

A coronal mass ejection in October 2003 shows up as a bright expanding ring around the sun. The inner white ring indicates the position of the sun's disc.

Great balls of fire

When the sun hurls flaming magnetic missiles at Earth, twin spacecraft carrying University-built instruments will sound the warning

By Deane Morrison

Oct. 24, 2006

In outer space as on Earth, real estate is all location, location, location.

That's particularly true for the twin spacecraft of NASA's STEREO mission, which will be positioned far apart in space to give the first binocular, or 3-D, view of the sun. On board are University-designed and built instruments to search for clues to how these explosions--the most powerful in the solar system--happen.

Launched the evening of Oct. 25, 2006, STEREO aims to learn more about the causes of spectacular eruptions of hot, magnetic bubbles of gas thrown off by the sun and how to identify those that are headed toward Earth, where they can disrupt power grids and communications. Seismology of the sun Known as CMEs (coronal mass ejections), the solar castoffs are an object of intense scientific interest. Through their experiment, called S/WAVES (STEREO Waves), University physicist Keith Goetz and colleagues at the University, the Paris Observatory and the University of California, Berkeley, will study radio waves and other signals tied to CMEs. Just as seismologists monitor ground tremors in hopes of identifying patterns that predict an imminent earthquake, the researchers want to find a pattern of solar activity that signals a CME is brewing. "It's all to understand and predict how the sun works," says Goetz, the project manager for S/WAVES. "We want to be able to look at the surface of the sun and say, for example, 'There's going to be an eruption--right there, in that spot.'" CMEs owe their capacity for mischief to electrically charged particles and magnetic fields embedded within them. Any doubt about their destructive potential was erased in March 1989, when the sun unleashed a CME that hit Earth's magnetic field and knocked out power to six million Quebec residents. The same electrical storm startled Minnesotans who turned on their radios only to find themselves eavesdropping on transmissions from the California Highway Patrol.

"STEREO is world class," Goetz says. "It's cool to create a sophisticated scientific instrument to fly in space."

CMEs can also shut down satellites and send astronauts in orbit running for the shelter of their radiation shields.

Here comes the sun

>CMEs explode from the sun's corona, the wispy thin but sizzling--two million degrees F--outermost layer of the solar atmosphere.

>The sun has no solid surface, just layers of atmosphere that extend beyond Earth. Our planet is in the outer, cooler part of the corona.

>Packing the punch of a billion megaton bombs, a typical CME hurls a billion tons of the corona through space at up to 2.5 million miles per hour.

>CMEs follow the 11-year solar cycle, surging and ebbing in roughly the same rhythm as sunspots. About five CMEs per day are normal at the peak of solar activity, about one every other day when solar activity is minimal.

>The sun's energy varies no more than one-tenth of one percent over a decade.

>CMEs can cause outstanding displays of northern lights.

>According to the leading theory of CME formation, the eruptions are like the release of a balloon that strains at its guy wires--magnetic lines of force--until they snap.

>The sunbeams you saw today began in the sun's center hundreds of thousands of years ago.

Source: NASA

"As our society becomes more electronic and sophisticated, these outbursts become more disruptive," says Paul Kellogg, a retired University physics professor. "STEREO will allow us to see when one is coming to Earth." Following the launch, the two STEREO (Solar TErrestrial RElations Observatory) spacecraft will use the moon's gravity as a slingshot to send them into orbit around the sun, one ahead of Earth and the other behind. Over the next four years, they will drift steadily away from the Earth and from each other. Taking advantage of their widely separated positions, onboard cameras will beam back clear 3-D views of any CMEs that erupt and the direction they're traveling. As CMEs plow through interplanetary space, they encounter the solar wind--the constant stream of charged particles flowing from the sun--and pound it like a piston. This generates a shock wave akin to a sonic boom. The shock also generates radio emissions that can be picked up by S/WAVES antennas. "We can see the invisible shock front as it propagates," Goetz explains. "We can tell how fast it's going and where it's going." Payoff of persistence The STEREO launch culminates five years of effort to integrate antennas, signal and data processing units, and all manner of other software and hardware into a compact experiment. As project manager, Goetz has worked closely with the teams in Paris and Berkeley and with fellow University physics graduate Steve Monson, who has built much of the hardware. "Keith and Steve are what makes it possible for us to have an experimental space program here," says Kellogg. "Without them, we wouldn't be able to design and build space experiments." Also on the project at the University were Al Knutson and Ron Bystrom, technicians known for their ability to build any apparatus to order. Together, the S/WAVES team has built a dual set of instruments that rank with the best in the world. Perhaps no one is looking forward to S/WAVES data more eagerly than University physics professor Cynthia Cattell. "I'm the lucky person who gets to come in and harvest all the hard work by Keith and his team," says Cattell. "Graduate students and undergraduates I supervise will get to analyze data and do exciting fundamental science on shock waves and how radio waves are generated. For students, it's a unique opportunity to come in on the beginning of a project that will yield a lot of exciting new results." To Goetz, STEREO is a chance to work on a top-notch mission and have fun with it. "If University space physicists want to do world-class science, they need world-class instruments on world-class spacecraft missions. And STEREO is world class," he says. "It's cool to create a sophisticated scientific instrument to fly in space."

See the STEREO Web site for animations and more about the project. STEREO is the latest in a long line of NASA missions for University space physicists.