Next month NASA will launch a pair of spacecraft that will help astronomers study and predict gigantic eruptions from the sun. Currently, the nature and causes of these explosions of high-energy particles and magnetic storms are poorly understood. And being able to predict them farther in advance will help prevent damage to satellites orbiting the Earth.
Coronal mass ejections–giant clouds of high-energy particles and magnetic disturbances that erupt from the sun–can damage satellites when the Earth is in their path. (A pair of them are shown here.) (Credit: SOHO/LASCO C2 consortium)
In the past, astronomers have been able to look at these solar storms, called coronal mass ejections (CMEs), only from the Earth. This limited perspective has made predicting the exact timing and extent of the solar storms difficult, says Janet Luhmann, a researcher at the University of California at Berkeley’s Space Science Laboratory, who helped design instruments for the new spacecraft. She compares it to “being run over by a truck: we don’t see the full velocity and size of what’s coming at us.” The two new NASA spacecraft, called STEREO, will orbit the sun in front of and behind the Earth, giving a far better view of the solar storms.
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Michael L. Kaiser, a STEREO project scientist at NASA, says a CME currently occurs every few days. The frequency of CMEs is expected to increase substantially, though–to several every day–in about five years when the sun reaches a peak period of activity. (Astronomers don’t know why, but the sun’s activity varies throughout an 11-year cycle.) Most CMEs don’t affect the Earth, but when they do, satellites can be damaged or even wrecked.
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The impact of CMEs on Earth can currently be predicted as many as four days in advance, but only within a 12-hour window. “We’ve got to do a better job,” says Kaiser.
Coronal mass ejections, which originate in the sun’s outer atmosphere, have two components. One is an enormous cloud of plasma, X rays, radio waves, and visible light. These energetic particles are accompanied by a large, fast-expanding magnetic loop. CMEs cause space weather–conditions that affect altitudes 50 kilometers above the Earth’s surface and higher (the upper atmosphere and beyond into the ionosphere and magnetosphere). In these regions, the influx of high-energy charged particles and magnetic storms caused by CMEs can interfere with satellites.
STEREO will carry multiple instruments, including 3-D imagers and particle and magnetic field detectors. Luhmann says that the mission in part is a test of the concept of “parking” a space weather satellite to predict the impact of solar storms on the earth.
Kaiser says that because satellites depend on microelectronics, they are very sensitive to small changes in current and voltage. Magnetic disturbances from CMEs can wipe out satellite computers’ memory. Luhmann says severe CMEs can actually shift the Earth’s magnetic field, leaving satellites orbiting above the equator outside the field.
Satellites orbiting in interplanetary space, outside the Earth’s protection, get a high dose of radiation during a CME; their solar panels are usually degraded. Kaiser cites a two-week period in 2003, called the Halloween storms, during which 20 CMEs, including some of the biggest ever recorded, damaged “almost every spacecraft.”
Solar storms can also affect the transmission of radio waves through the ionosphere, which can corrupt GPS signals. Kaiser says the oil industry is very interested in space weather prediction because it relies on GPS to guide offshore drilling. “If there’s a solar storm in process…their GPS could be off,” he says. CMEs can also cut off airplanes’ radio contact when flying over the poles, as many long international flights do. When CMEs are predicted, airlines must reroute on short notice.
With warnings further in advance, says Kaiser, satellite operators “could power down or standby [their satellites]. It’s like turning off the TV during a lightening storm.”
