Magazine article New Statesman (1996)

Fending off Killer Electrons

Magazine article New Statesman (1996)

Fending off Killer Electrons

Article excerpt

If you were to design a planet suited for life, it's hard to imagine improving on the earth. Our planet has hidden life-protection systems that continue to surprise us.

Last month, astronomers discovered a magnetic deflector shield sitting 11,000 kilometres above our heads. It protects the surface of our planet from high-energy-charged particles that would otherwise bombard us with radiation. These "killer electrons" are halted by nothing more than a thin sheet of plasma--a gas made up of charged particles--held in place by the earth's magnetic field. It's a puzzling phenomenon: no one knows why such a shield should form.

Life needs shelter from the storms of space. Far from being an empty, neutral environment, space is deadly, packed with cosmic rays, particles that whizz around at near-light speed. This is what will make interplanetary travel so dangerous for human beings.

When astronauts in orbit close their eyes, they are beset by flashes of light under their eyelids. The flashes are stimulated as cosmic rays shear through their eyeballs and brain tissue. We already knew that long stretches in space could lead to radiation-induced cancer. A 2013 study in which mice were irradiated at levels astronauts experience in space showed that they should fear the quick onset of radiation-induced Alzheimer's disease, too.

On earth, we are protected from this by the magnetic field generated in the sphere of churning, molten metal 3,000 kilometres beneath our feet. This is earth's outer core. It is powered by heat left over from the planet's formation, radioactivity within the core and the planet's spin on its axis.

It is the motion of flowing metal that creates the magnetic field and thanks to the extraordinary volume of churning metal beneath our feet, earth's field is strong enough to reach into space. There, its interaction with interplanetary space's clouds of charged particles has created two fixed cloaks of plasma. …

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