On 2 September 1859, a giant ejection of matter and magnetism erupted from the sun and struck Earth. Auroral storms burst over two-thirds of the planet鈥檚 skies, compasses went haywire, and the telegraph system across the world malfunctioned as phantom currents surged through the wires.
Named after the British amateur astronomer Richard Carrington 鈥� who took observations of it 鈥� to most on the ground the Carrington event was little more than a spectacular light show. Today it would be a disaster, thanks to our reliance on electromagnetic technologies. Satellites could burn out, and our communications and positioning systems with them. Transformers could be destroyed, bringing down power grids across nations. Public transit would grind to a halt. In 2008, the American National Academy of Sciences estimated that a Carrington event could cost the US economy alone $2 trillion.
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Since then, in the UK . The key to protecting ourselves is to understand the sun鈥檚 capricious magnetism. Seen in visible light, the sun appears constant. Change your view to ultraviolet or X-rays, however, and a different picture emerges; dark regions known as coronal holes come and go on timescales of days, weeks, months or years. These holes can span 50 times the diameter of Earth.
Hidden dynamo
It is here that the sun鈥檚 magnetic field stretches out into the solar system, releasing gas from the sun鈥檚 atmosphere, the corona, that becomes the solar wind. The trouble is that we can鈥檛 predict when and where these holes and ejections will happen. 鈥淲e don鈥檛 know how the sun鈥檚 magnetic cycle works,鈥� says Tim Horbury of Imperial College London.
We do know that they come and go on a roughly 11-year cycle, and we are currently in a declining phase. But that鈥檚 about it. Apart from some vague conjectures about the churning of the hot plasma, exactly how the sun generates its magnetism remains an impenetrable mystery.
The European Space Agency鈥檚 could change all that. Launching in 2018, it will fly close to the sun, inside the orbit of Mercury. Horbury is the principal investigator of its magnetometer, one of 10 instruments that will study the sun in unprecedented detail. The mission will measure the magnetic fields associated with these coronal holes. It could provide the key to unlocking the mystery of the sun鈥檚 magnetic dynamo 鈥� and just might help civilisation avoid an inadvertent return to 1859.
Read more: The 6 greatest mysteries in the solar system
(Image: SOHO (ESA & NASA))
This article appeared in print under the headline 鈥淲hy is the sun magnetic?鈥�
