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Probe to Offer 3-D View of Stormy Sun
2006 09 18

By Irene Klotz |

Solar Terrestrial Relations Observatory
This artist's illustration shows NASA's Solar Terrestrial Relations Observatory, or STEREO. The pair of orbiting probes will offer a first 3-D look at the sun, allowing scientists to predict the timing and strength of solar storms.

As the sun begins its next 11-year cycle, scientists expect to have a much better view of the massive explosions of solar particles that can shut down power grids, short-circuit satellites and threaten the health of astronauts orbiting Earth.

Their hopes rest aboard a rocket at Cape Canaveral Air Force Station in Florida that is being prepared for liftoff Sept. 18.

The ship will carry a pair of nearly identical spacecraft called the Solar Terrestrial Relations Observatory, or STEREO, which will add another perspective to our view of the sun.

Just as we can sense depth because of the slight offset of our eyes, the STEREO satellites will look at the sun from different positions in space to produce three-dimensional images.

One spacecraft will settle slightly closer to the sun, orbiting every 346 days. The other will be located just behind Earth and take 388 days to orbit. From the sun's perspective, the probes will be at a 45-degree angle from each other.

By combining data from the two, scientists will get an unprecedented view of the sun and for the first time be able to pinpoint where the solar storms are headed. They expect to be able to more precisely predict when potentially disruptive solar eruptions, called coronal mass ejections, threaten Earth.

"Right now we can only see the sun, essentially, in just two dimensions," said STEREO deputy project scientist Terry Kucera. "We can't tell in some cases whether coronal mass ejections are moving toward us or away from us. That's pretty fundamental."

"With 3-D, we'll be able to tell basic things like how fast is it going is it speeding up or slowing down," he added. "These are important things that we need to know if we're going to be able to predict what the impact of a particular event is going to be."

Coronal mass ejections are huge bubbles of charged particles that erupt from the sun's outer atmosphere shortly after a solar flare. Just one eruption can send more than a billion tons of solar particles into space.

The charged particles trigger the beautiful aurora seen in the northern and southern skies, but they have a dark side as well.

A massive solar storm in 1989, for example, took out a power grid in Canada, shutting off electricity for 6 million residents. And three years ago, Japan lost contact with its ADEOS-2 environmental satellite after a series of solar eruptions.

"In terms of space-weather forecasting, we're where weather forecasters were in the 1950s," said Michael Kaiser, STEREO project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.

"They didn't see hurricanes until the rain clouds were right above them."

"In our case, we can see storms leaving the sun, but we have to make guesses and use models to figure out if and when they will impact Earth," he said.

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