More than a year after the sun lashed out at Earth with the most powerful set of storms ever recorded, a fleet of space probes continues to track the reverberations. The data document in frightening detail how the sun’s outbursts buffet Earth and the other planets of the solar system.
The action began around Halloween 2003, when a series of solar flares caused huge eruptions, known as coronal mass ejections, on the surface of the sun. Within minutes after the first flare, Earth was rocked with radiation. A squall of subatomic particles, including electrons and protons, raced out at 5 million miles per hour and slammed into our magnetic field, which deflected most of the blow. Still, airplanes had to be rerouted away from polar flight paths, satellite communications were disrupted, and astronauts in the International Space Station scurried for cover in the heavily shielded Russian-built part of their orbiting home.
A few hours later, the Mars Odyssey spacecraft recorded the same solar storm ripping loose parts of the thin Martian atmosphere and flinging them into space. In succession, the Ulysses probe, near Jupiter, and Cassini, then approaching Saturn, picked up emissions as the still-potent stream of particles rammed into those planets’ magnetic fields. “Most surprising is that the blast wave was still strong enough to cause significant effects in the atmosphere of Saturn, which is nearly a billion miles from the sun and has a magnetic field much larger than Earth’s,” says Ed Stone of Caltech, chief scientist of NASA’s Voyager program.
In April Voyager 2 detected the passing wave 7 billion miles from the sun. By now the blast should be knocking at the heliopause, the boundary where the solar wind rubs up against a countervailing flow of interstellar winds. The Halloween storms may stir the heliopause sufficiently to create radio noise that Voyager can detect.
“Solar disturbances have always been there, but they were not important before we became a technological society,” says Stone. “We have to understand these effects because things like power grids and satellite systems are sensitive to them. This is important, too, if we ever expect humans to venture into deep space.”