Space / Space Flight

Some of Lin’s observations agreed with existing theories, and some made no sense at all. According to the leading theory, a flare is set off when nearby magnetic fields of opposite polarity break and reconnect, creating a closed loop with two footprints on the solar surface. High-energy protons and electrons come screaming out of the reconnection site, flow along the loop, and crash into the denser plasma at the sun’s surface. The electrons release a salvo of X-rays when they collide with the atoms. The protons are powerful enough to smash an atom’s nucleus and create all sorts of exotic by-products, including antimatter. The antimatter doesn’t last long. Positrons (antielectrons) meet up with electrons and annihilate each other, releasing ultrahigh-energy gamma rays. Lin estimates that the July 23 flare manufactured about a pound of antimatter, enough to power the entire United States for two days.

As expected, Lin’s images showed big X-ray sources at the two footprints and a 40-million-degree afterglow that he believes marks the reconnection site. But there was also a mystery: The protons didn’t stay on the same loop as the electrons, as theory would predict. They crashed to the surface about 10,000 miles away from the electron footprints. Craig de Forest, a solar physicist at Southwest Research Institute in Boulder, compares the phenomenon to dynamiting a hillside only to discover that all the dirt has gone in one direction and all the gold in another. “This upsets the canonical picture,” Lin says. “People are beginning to think about what it means, but there’s not a satisfactory idea yet.”

Three flares from last autumn’s storms produced measurable gamma rays, and one of the flares produced at least seven times as many as the July 2002 flare. Analyzing these recent events may allow physicists to determine the significance of the unexpected distribution observed in the 2002 flare. “With the new flares, we want to do an even better job than we did last time,” says Lin.

All the new data may provide a window into the life cycles of stars and open up the sun’s past. Many other stars are known to have flares, many more violent than the sun’s. But even ordinary G-class stars like our own have been known to double in brightness for a period of a few minutes to a few days. These rare events, called superflares by astronomer Bradley Schaefer of Louisiana State University in Baton Rouge, are 100 to 10 million times more powerful than anything our sun has dished out in human history.

If a large superflare happened on our sun, says Schaefer, it would cause an ecological holocaust on Earth. “Even a medium-size superflare would cause mass extinctions,” he says. “The reason is ozone depletion.” Radiation bombarding the upper atmosphere would obliterate the protective ozone layer, rendering us defenseless against ultraviolet light. Some astronomers speculate that Earth could have experienced a superflare in the distant past. Superflares would be more common in younger stars, they reason, because they spin faster and have stronger magnetic fields.

Even now, the ozone layer is not completely safe from solar attack. One of the unexpected consequences of the October 28 flare was a fivefold increase in ozone-destroying nitric oxide at 70 miles above Earth’s surface. The increase lasted less than two days, and it doesn’t seem to have bothered the ozone layer, which lies 40 miles below. Still, the solar weather watchers at NASA are puzzled. “We don’t really know what this means,” says Chris St. Cyr. “I wouldn’t say it’s disturbing, but it is curious.”

Across San Francisco Bay from Lin, a group of scientists at Stanford University is looking at the sun’s interior through a remarkable technique called helioseismology. The method uses optical sensing devices to detect movement of solar gases, much as seismologists can detect tremors in the earth. “There are sound waves going every which way in the sun,” says group member Philip Scherrer, one of the 12 principal investigators for the Solar and Heliospheric Observatory (SOHO), a joint project of NASA and the European Space Agency. The sound waves come from the churning of gases in the sun’s convective layer. In SOHO videos, the sun appears to have hundreds of thousands of flickering lights on its surface. Each flicker, called a granule, is a column of gas about 600 miles wide, which vibrates up and down about once every five minutes. Think of each one as a 600-mile-wide drumhead and you can understand why the sun is a noisy place.

 Monitoring a Tempestuous and Unpredictable Powerhouse

The sun converts 4 million tons of matter into energy every second. The reactions occur in its core, where hydrogen is compressed to such intense heat that helium forms and energy is released. Today the sun consists of mostly hydrogen (78 percent) and helium (20 percent); the rest are heavy elements. Solar physicists calculate that the sun is about halfway through its 12-billion-year life span. It is currently a yellow dwarf, a star that is average in size and temperature. In 7 billion years, it will balloon to 250 times its current size and become a red giant. About half a billion years later, it will contract to a tiny white dwarf one-hundredth the size it is now. Ultimately, it will become a black dwarf—a hunk of matter that no longer emits light. Although physicists can project the sun’s life span, they have many questions about its inner life. The foremost question is, what causes the magnetic fields that drive solar phenomena?

Corona

Ionized gases extend millions of miles away from the solar surface. During an eclipse the corona is visible as a bright halo around the sun. The corona is extremely hot—1,800,000°F. The cause of this intense heat is unknown.

Magnetic forces that form around Earth protect the planet and humankind from most of the intense solar activity. Interactions between the magnetic fields of Earth and the sun produce the beautiful polar phenomena known as auroras.