THE weather on Earth is hard enough to predict, let alone control. But we might have more luck with space weather. An electrical engineer has proposed that satellites beaming out radio waves would help drain high-energy particles from Earth鈥檚 radiation belts, averting the worst ravages of solar storms.
The sun regularly hurls huge bursts of charged particles at the Earth, which boost radiation levels and cause magnetic storms and auroras when they hit the planet鈥檚 magnetic field, or magnetosphere (see Graphic). Many of the charged particles get trapped in regions of the magnetosphere called the Van Allen belts, which extend from 60,000 kilometres above the Earth down to about 1000 kilometres above the equator.
Global positioning satellites orbit in the Van Allen zone, as do many other communications and imaging satellites, and the radiation onslaught can damage their hardware. A few satellites have failed outright during the most severe solar storms. Even when satellites survive, the radiation makes critical electronic components degrade faster, shortening their lifetimes.
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Now Umran Inan, who is head of Stanford University鈥檚 Space, Telecommunications and Radioscience Laboratory in California, suggests that radio waves could help protect the satellites. Researchers have known since the 1970s that very-low-frequency (VLF) radio signals can push the electrons out of the belts鈥� magnetic trap. They leak out at the poles, where they are absorbed into the upper atmosphere. This drainage does occur naturally, but in 1998 researchers realised that VLF radio transmissions from Earth are now responsible for most of the drainage.
Inan proposes using a similar effect to speed up the process after solar storms (Journal of Geophysical Research, DOI: 10.1029/2002JA009580). The best frequencies for this are below 17 kilohertz, but terrestrial transmitters would require impractically large antennas to achieve sufficient intensity. However, Inan has worked out that satellites could do the job much more efficiently.
He calculates that a satellite emitting just 13 watts at 2.5 kilohertz should halve the amount of time that the electrons spend in the belts before draining away. Satellites stationed around the belts could be turned on after an outburst, then switched back off when particle densities had dropped to a safe level.
Although it is currently unclear who would pay for such a system, the damage caused by solar storms is a growing problem for satellite operators. Numbers of satellites are increasing, and as integrated circuit elements shrink, they become more susceptible to radiation damage. Metal shielding and radiation-hardened components are available, but it鈥檚 cheaper just to build spare satellites.
The system could also help clean up space in the event of a nuclear explosion, which would throw enough high-energy particles into the atmosphere to knock out satellites. 鈥淧eople in defence circles are very interested in this sort of thing,鈥� says Inan, whose study was partly supported by the US Air Force.
Space scientists who have struggled to control radiation damage to satellites are intrigued by Inan鈥檚 idea. Yet they remain wary because our understanding of the Van Allen belts is so limited. We don鈥檛 know what the natural state of the belts is, partly because just months after James Van Allen discovered them in 1958, the US detonated two nuclear bombs above the south Atlantic, swamping the belts with particles.
And since then, radio transmissions have been affecting the speed at which the particles in the belt drain away. 鈥淚 hope we know for sure that the occasional high densities of radiation in the magnetosphere aren鈥檛 subtly good for something,鈥� says Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics.