Solar flare reveals physics of an angry sun

Fourth-largest flare turned out to be more irritation than calamity.

In the end, there were no massive power outages, no widespread collapses of cellphone service, no communications meltdowns. The toxic solar stew that swamped Earth Wednesday and Thursday - threatening satellites above the Earth and power stations on it - was just a warning.

This, after all, was intense but not unique. For countless millenniums, the furnace of the sun has belched particles of pure energy toward Earth in flares - solar explosions millions of times more powerful than that of a hydrogen bomb. And during that time, they have been fended off with apocalyptic fury in the upper reaches of the atmosphere - yet seen on the surface only as curtains of ethereal color in the night sky.

Now, however, there are satellites in that ether, and this week's solar assault suggests that the more we learn about our still-mysterious star - and the more we build on technology sensitive to it - the more we are realizing that Earth, at times, is the servant of an angry sun.

"These things do impact people living down on Earth," says Ron Zwickl, deputy director of the National Oceanic and Atmospheric Administration's (NOAA) Space Environment Center in Boulder, Colo.

The seeming paucity of problems emerging after this week's event - limited early Thursday to the loss of contact with one Japanese satellite and a forced shutting down of another - belies its potential impact. Scientists note that the magnetic orientation of the storm limited the damage. Still, smaller storms that have spouted from the same region of the sun could have greater affect on Earth today.

In other instances flares have had dramatic effects. A 1989 flare knocked out a Quebec power grid when the surge in solar energy overloaded the system, and a 1859 event caused fires when telegraph wires shorted out.

The Federal Aviation Administration is testing a warning to airlines during solar flares, allowing them to avoid polar routes at high altitudes, which are more vulnerable to radiation as well as energy surges that could knock out radio equipment. Airlines, in fact, reported the loss of some radio contact in high latitudes Wednesday, and Dr. Zwickl says he knows of airlines that have altered routes due to such warnings.

Still, flares that can cause serious damage are rare. In general, they need to be larger than normal to trouble Earth's defenses - a thick atmosphere and the magnetic shield that holds it in place. Moreover, they need to occur directly in the middle of the side of the sun facing the Earth - aimed directly at the planet.

The solar flare that billowed from the sun on Tuesday and buffeted Earth 18 hours later seemed to fit both criteria: By some measures, it was the fourth-largest solar storm ever recorded, and it was pointed straight at Earth. "It packed a pretty good punch," says Zwickl.

In a cosmic coincidence, gathering more knowledge about solar flares swings in a precarious balance: The House Committee on Science scheduled a hearing for Thursday to decide on cutting funding for NOAA's space weather-forecasting operation by at least 40 percent. The success of marking the event, followed by the difficulty of predicting damage, shows both how much scientists have learned about the sun - and how much they still don't know.

Only 45 years ago, astronomers scoffed when a colleague suggested that the sun's atmosphere extended as far as Earth. Now, scientists know it extends well past Pluto. The Voyager spacecraft, now more than 13 billion miles from the sun, is still recording particles borne on the solar wind created by the sun.

Flares are simply solar eruptions that strengthen the solar wind, born of a stellar process that literally twists and tortures the star until a section of its surface explodes to release the tension. The tension, scientists believe, builds up because the middle sections of the sun rotate faster than the poles. This distorts the sun's magnetic field, pulling it faster in the mid-latitudes, until it becomes a potent tangle of magnetic current, coursing beneath the sun's skin.

At the places where the current breaks through and reenters, a pair of sunspots form - dark regions where the current has retained huge quantities of energy. Eventually, the region bursts in a reek of solar detritus tens of millions of miles long: a solar flare.

It is but one glimpse of the power of nature's perfect furnace, stoked by matter packed so densely that it takes a gamma ray 10 million years to escape - a distance that would normally take less than three seconds outside the sun.

How this cosmic bellows generates solar flares, or how its magnetic field appears to untangle and reorient itself every 11 years, however, remains unanswered. But sorting out such questions is crucial to a fuller understanding of the sun, and perhaps to a way to forecast solar flares, rather than responding to them.

"We'd like to be able to predict these," says Jack Harvey of the National Solar Observatory in Tucson, Ariz. "We want to understand how the energy starts to create one of these events."