Sun Cast in New Light by Satellites

March 1, 2007 — Twin satellites taking three-dimensional images of the sun have returned their first images, fulfilling scientists' hopes for a tool that could significantly improve forecasts of potentially dangerous space weather.

"Nobody ever died looking at an aurora, but some of the other disturbances are getting to be a problem," said project scientist Michael Kaiser with NASA's Goddard Space Flight Center in Greenbelt, Md.

Aurora, the shimmering lights that appear over Earth's polar regions, are benign manifestations of high-energy particles streaming off the sun's corona and hitting Earth's magnetic field.

When the eruptions are intense, the charged particles can wipe out computer memory, short circuit power grids and interfere with air-to-ground radio transmissions.

Before the two-part Solar Terrestrial Relations Observatory, or STEREO, was in orbit, scientists could make predictions about a solar storm's intensity and direction only about 12 hours before it hit Earth.

Now scientists expect to be able to trace a storm's progress from the moment it leaves the sun, said Naval Research Laboratory solar physicist Russell Howard, a STEREO principal investigator.

"Previous imagery did not show the front of a solar disturbance as it traveled toward Earth, so we had to make estimates of when the storm would arrive," he said. "With STEREO, we can track the front from the sun all the way to Earth."

The images released Thursday were taken in December as the twin STEREO probes settled into their working orbits, which include swings around the moon.

By combining the views from the two satellites, scientists will be able to piece together a three-dimensional picture of the sun, much as human eyes, set slightly apart in the head, can render a stereographic view of the world.

The satellites were launched Oct. 26 aboard a single unmanned booster.

Of particular interest to the STEREO team are violent solar storms known as coronal mass ejections, which can blow up to 10 billion tons of the sun's atmosphere into space. The particles blast away from the sun at speeds of about 1 million mph.

Upon reaching Earth, the particles interact with Earth's magnetic field, triggering storms that can damage or destroy satellites and shower unprotected astronauts with radioactive particles.

The storms can also cut off radio communications aboard airplanes flying polar routes.