A MAJOR solar storm would not only damage Earth's infrastructure, it could also leave a legacy of radiation that keeps killing satellites for years.
When the sun belches a massive cloud of charged particles at Earth, it can damage our power grids and fry satellites' electronics. But that's not all. New calculations suggest that a solar megastorm could create a persistent radiation problem in low-Earth orbit, disabling satellites for up to a decade after the storm first hit.
It would do this by destroying a natural buffer against radiation - a cloud of charged particles, or plasma, that normally surrounds Earth out to a distance of four times the planet's radius.
The relatively high density of plasma in the cloud prevents the formation of electromagnetic waves that would otherwise accelerate electrons to high speeds, turning them into a form of radiation. This limits the amount of radiation in the innermost of two radiation belts that surround Earth.
But solar outbursts can erode the cloud. In October 2003, a major outburst whittled the cloud down so that it only extended to two Earth radii. A repeat of a huge outburst that occurred in 1859 - which is expected - would erode the cloud to almost nothing.
Yuri Shprits of the University of California in Los Angeles led a team that simulated how such a large storm would affect the radiation around Earth.
They found that in the absence of the cloud, electromagnetic waves accelerated large numbers of electrons to high speed in Earth's inner radiation belt, causing a huge increase in radiation there. The inner radiation belt is densest at about 3000 kilometres above Earth's equator, which is higher than low-Earth orbit.
But the belt hugs Earth more tightly above high latitude regions, overlapping with satellites in low-Earth orbit.
Speeding electrons cause electric charge to accumulate on satellite electronics, prompting sparks and damage. Increasing the number of speeding electrons would drastically shorten the lifetime of a typical satellite, the team calculates (Space Weather, DOI: 10.1029/2011sw000662).
The researchers say that the destructive radiation could hang about for a long time, spiralling around Earth's magnetic field lines. In 1962, a US nuclear test carried out in space flooded low-Earth orbit with radiation that lasted a decade and probably ruined several satellites.
"When you get this radiation that far in, it tends to be quite long-lived and very persistent," says Ian Mann of the University of Alberta in Edmonton, Canada, who was not involved in the study.
Thicker metal shielding around satellite electronics would help, says Shprits. The persistent radiation would also be hazardous for astronauts and electronics on the International Space Station.
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