For solar scientists, the new sun-studying SOHO satellite is an eye-opener. Its view, undistorted by Earth's atmosphere, has revealed a previously unknown kind of solar eruption that directly affects our planet.
The eruptions are produced when a magnetic trap circling the sun's equator collects electrically charged particles. This trap forms a magnetic "inner tube" of these particles around the sun that fills and eventually bursts. Then, unlike the well-known flares that eject narrow jets, this outburst becomes a global event because it shoots out highly energetic particles in all directions.
While this discovery is important for scientists, it is equally important for everyone on Earth who depends on electric power lines or electronic communications. Streams of energetic solar particles laced with magnetic field lines can damage satellites. They interact with Earth's magnetic field in ways that disrupt radio communications and power lines. That's why the United States and some other nations run solar-flare forecasting services.
In reporting the new discovery, Guenter Brueckner of the Naval Research Laboratory in Washington says that this may account for magnetic storms that have caught the flare forecasters by surprise. The sun now is in its so-called quiet phase near the minimum of the roughly 11-year sunspot cycle. Dr. Brueckner notes that there are no sunspots or flares right now. But there is plenty of what he calls "huff and puff" going on with this newly discovered eruptive mode. The good news, he adds, is that as scientists work through the SOHO data, "I think we may have something that will be predictive." It may be possible to give several days warning of a potentially disruptive event at Earth.
Explaining this during the spring meeting here of the American Geophysical Union, Brueckner says that during this sunspot minimum, magnetic fields from the sun's more northern and southern regions sometimes bend toward the equatorial zone. They form a magnetic structure that accumulates electrically charged particles like an tire tube filling with air. Instruments such as the one Brueckner's team uses on SOHO can monitor the buildup and outburst of these particles. This holds out the possibility of providing timely warnings.
Brueckner is the principal investigator for an international team using SOHO's Large Angle Spectro Coronograph. Blocking the sun's glare with a small shield, it can study the solar atmosphere, called the corona, out to distances of 30 solar radii. The solar radius is about 433,000 miles.
This is one of 12 instruments on the Solar and Heliospheric Observatory (SOHO) spacecraft, which is a joint project of the European Space Agency and NASA. ESA and NASA roughly split the projects $1 billion cost.
Launched last Dec. 2, SOHO has already shown that the term "quiet" sun for this phase of the solar cycle is an oxymoron. Earlier this month, investigators with various SOHO instruments reported finding unexpected activity. Now updated reports by Brueckner and others at this meeting reinforce that judgment.
For example, Jean-Pierre Delaboudinire of the Institute for Space Astrophysics at Orsay, France, says his group is finding activity all over the sun's surface. It bubbles up for tens of seconds up to nearly a month. Dr. Delaboudinire is chief investigator for the Extreme Ultraviolet Imaging Telescope that observes the sun by ultraviolet light. He says it is "obvious" that "activity is not limited to the magnetically intense active regions" as had been supposed.
SOHO is one of a fleet of spacecraft taking part in the International Solar Terrestrial Physics series of missions to study the sun and its influence on Earth. SOHO's job is to study the sun from a point where the gravitational forces of sun, Earth, and Moon effectively cancel. Hovering there, it has a clear 24-hour solar view.
The craft has enough maneuvering fuel to stay on station for 30 years. However, its mission currently is funded for only two years. Brueckner says that given the surprises SOHO has already delivered, he "wouldn't like to predict" what it might find when the sun returns to its active phase by 2000. But he says he would predict that "this spacecraft delivers such spectacular results [that] nobody is going to shut it down."