Stormy Weather

A m

illion miles from the earth, NASA's Advanced Composition Explorer (ACE) spacecraft suddenly found itself under assault. Late in January, the tiny, instrument-packed spacecraft was buffeted by an exceptionally powerful burst of particles spewed out by the sun. In the space-environment control room at the National Oceanic and Atmospheric Administration (NOAA) headquarters in Boulder, Colo., alarms sounded. "All of a sudden, a blast wave of solar wind showed up at the ACE spacecraft," says NOAA's Joe Hirman, "as dense as any we've seen, and, bam, 30 minutes later the earth's magnetic field got hit hard."

A few days earlier, the Solar and Heliospheric Observatory (SOHO), high above the earth, had captured images of another solar phenomenon--an unusually large prominence, a loop of fiery gases 800,000 miles wide, erupting from the sun's surface. It was also recording increasing numbers of flares --exceptionally hot blotches on the solar surface--and a proliferation of sunspots migrating inexorably toward the sun's equator.

To astronomers, such events signal an approaching solar maximum, a period of great turbulence that roils the sun every 11 years or so. The last solar max occurred in 1989. Now the sun, right on schedule, seems headed toward a peak of activity later this year.

During solar maximums, space weather becomes stormy. The normally benign sun pounds the earth mercilessly with ultraviolet radiation, X rays and floods of charged particles, distorting the planet's protective magnetic field and inducing powerful electric currents that can wreak havoc not only with spacecraft but also with many aspects of terrestrial life.

One 1989 solar storm knocked out Hydro-Quebec transformers, leaving 6 million people in eastern Canada and the U.S. Northeast without electricity for nine hours. The same storm disrupted shortwave radio transmissions, crippled Coast Guard loran navigation systems and had automatic garage doors opening on their own.

In the years since, we have become increasingly dependent on satellite-based communications, and even off-peak solar outbursts have caused trouble. They are suspected in damage to at least a dozen satellites, and the failure of the Galaxy IV satellite during a 1998 solar storm that silenced 80% of North America's pagers. In the past four years alone, says Chris Kunstadter, of U.S. Aviation Underwriters, space losses may have exceeded $550 million.

Since the last maximum, the number of satellites in orbit has increased sixfold, to more than 600. They are essential for everything from telephone service and air-traffic control to connections, pay-at-the-pump credit-card service and hundreds of other information-age conveniences. Yet for reasons of economy, or just plain indifference, few of these spacecraft are properly shielded.

The key to the sun's energetic fury is, in a word, magnetism. "Control magnetic energy, and you control the universe," says University of Colorado astrophysicist Daniel Baker, paraphrasing a character in the old Dick Tracy comic strip. If the sun were a rigid body, its magnetic field might resemble the earth's, with symmetrical field lines like a bar magnet's. But as the sun turns, its equatorial gases rotate faster than those at higher latitudes, twisting the magnetic lines "like a rubber band," explains David Hathaway, a solar physicist at NASA's Marshall Space Flight Center.

Under increasing tension, the magnetic field eventually breaks through the surface. This produces sunspots, darker magnetized regions of relatively cooler gases. When regions of opposite polarity meet, prodigious amounts of pent-up magnetic energy are released as heat. The upshot: coronal mass ejections--the spewing out of billions of tons of solar material--and giant flares.

What ACE detected last month was a violent gust of "solar wind," the constant flow of charged particles from the sun. Usually it streams past the earth at less than 1 million m.p.h., but when that wind gushed from a rare gap in the sun's tangled magnetic web, its velocity exceeded 2 million m.p.h. and particle density was 30 times normal.

"If you can imagine yourself sitting in a chair and suddenly being sprayed by a fire hose," says NOAA's Hirman, "that's what the solar wind did to earth that morning." Usually the earth's magnetic field acts as a shield. But the ill wind so squeezed it on the earth's sun side that the field slipped below the orbits of many satellites and briefly exposed them. Fortunately, no astronauts were aloft to experience the deadly particles.

Solar flares can also doom satellites. Reaching the earth in just eight minutes, their powerful UV and X rays help heat up and expand the atmosphere, thereby increasing molecular drag on low-orbiting satellites and shortening their orbital life-- as happened in 1989 to the Solar Max satellite, which was designed to study the very thing that did it in.

Perhaps the most spectacular effect of solar bombardments is on the earth's magnetic field. By causing it "to wobble and shake," explains NASA's Hathaway, it induces strong electric currents in the atmosphere and on the ground. In an instant, the surges destroy transformers, like Hydro-Quebec's, and overwhelm circuit breakers. The surges also corrode pipelines by weakening away the metal.