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Earth an Active Participant in Solar Storms - 2002-05-15

New U.S. satellite imagery shows that Earth's upper atmosphere puts up a mighty defense against the onslaught of solar storms, which bombard our planet with electrically-charged particles. Part of the upper atmosphere is lost in the battle, but what returns from the fray is so super-charged that it disrupts Earth's electrical systems and satellites. Scientists have discovered that Earth is not a passive victim in this process, but an active contributor.

Scientists once thought the space between the Earth and the sun was almost a vacuum. Now we know the sun fills it with gusts of hot, electrically-charged atomic particles called the solar wind. Sometimes the wind blows very hard. When the sun's outer layer is really active, it propels nearly one-third of its matter outward at supersonic speeds. A heavy blast can produce a shock wave that compresses the planet's magnetic field.

The resulting geomagnetic storm can wreak electrical havoc, shutting down spacecrafts, power networks, communications and other technical systems.

Does this sound like we are a mere victim of violent solar activity? That was the scientific view until a U.S. satellite called IMAGE sent back recent pictures that made the physical processes of space storms visible for the first time. "With this new vision, it was found that Earth is an active participant in space weather, not just a passive buoy flopping in the solar wind," he said.

Richard Fisher heads the division of sun-Earth science at the U.S. space agency NASA. "This is, in fact, a huge change in our thinking," he said. "IMAGE will rewrite textbooks on space weather and upper atmosphere physics."

Scientists poring over IMAGE satellite data have found one of nature's ironies: Earth's atmosphere shields us from most of the superheated solar wind, but as University of Michigan researcher Janet Kozyra explains, it also supplies much of the material that produces the damaging effects to Earth's technical systems. "The earth actively responds when it is engulfed by a solar wind disturbance," she said. "Our own atmosphere intensifies the storm by sending these particles out there."

Here's how it works. According to Johns Hopkins University space physicist Donald Mitchell, bursts of oxygen leave the atmosphere during a blast of solar wind. Most of the oxygen dissipates into space, but a fraction is trapped by Earth's magnetic field and ultimately encircles the planet, forming a powerful multi-million amp current along the invisible magnetic field lines. "It is a lot of energy there, It's gained about 100,000 times the energy that it had before it left the atmosphere," he said. "When they plunge into the atmosphere, these strong currents are generated, and this process transforms the mid-latitudes where we live from its usual calm state into a maelstrom that has direct effects on our daily lives."

In the process, about 100 tons of Earth's oxygen is lost in space. That sounds like a lot, but space physicist Stephen Fuselier of the Lockheed-Martin Advanced Technology Center says it is really only enough to fill a large enclosed sports stadium. "Over the course of billions of years, the loss is relatively slight," he said. "However, if there are time periods when the sun is more active, of course the loss increases. That is the price the Earth pays for interacting with the sun and protecting the atmosphere - it loses part of it."

The IMAGE satellite is the latest in a series of U.S., European and Japanese spacecraft studying the sun and its interaction with Earth. The previous orbiters give scientists about one hour's lead time to predict a space storm and warn operators of power grids, satellites and other electrical equipment that a blast is on the way.

But Janet Kozyra says the IMAGE data will help researchers develop better models to forecast the severity and impact of space storms. "We will be attempting to incorporate this information into these kinds of global models and produce a much-improved description of the space environment, much the same way that we used images from meteorological satellites to vastly improve our ability to predict weather," she said.

Ms. Kozyra calls IMAGE the first weather satellite for space.