How big can solar flares get?

On Nov. 10, 1989 there was a large solar flare.

This produced a coronal mass ejection or solar storm that arrived at Earth on Nov. 13, causing power outages and other damage totalling some $2 billion. The damage was mainly done to infrastructure—power, communications and transportation. In 1859, there was a far bigger solar flare.

Today we are far are more dependent on infrastructure than we were in 1989, with long supply routes and a critical dependence on the Internet, which touches almost all aspects of our lives, so an event like the 1989 flare would probably hurt us a lot more. A repetition of the 1859 flare would be extremely serious. The damage would total something like $2 trillion and take months to fix.

Losing the Internet for even a day would be very serious. We therefore need to have some sort of plan for the future to minimize the impact of solar activity and accelerate the recovery. The first step is to estimate what is the biggest solar flare we are likely to have. Events like this are called "Black Swans”. They might be very rare, but the consequences are so serious we cannot discount the chance of one happening.

Solar flares and coronal mass ejections are produced by stresses and instabilities in the Sun's magnetic fields. Stars are balls of plasma: matter so hot the atoms lose some or even all of their electrons. When we add plasma to magnetic fields we get something rather like rubber or elastic.

This stuff, often referred to as a "magnetoplasma", can be compressed, stretched, sheared or twisted. Just as we store energy in a rubber band by twisting or stretching it, deforming magnetoplasma stores energy in it.

On the Sun, the constant churning of material stores enormous amounts of energy in loops, bubbles, ropes and sheets of magnetoplasma - millions of hydrogen bombs' worth of energy, or more. Most of the time some sort of non-catastrophic stress relief happens, but sometimes this is not possible. Then, just as a snapping elastic band releases all of its stored energy in an instant, all the stored energy in a distorted lump of magnetoplasma can be released in seconds.

Somewhere in the distorted structure the stress becomes too much, instabilities are triggered and the magnetic fields snap. The instability rapidly spreads until there is a huge explosion, producing high-energy radiation, beams of accelerated particles and often ejecting a great chunk of solar material into space at thousands of kilometres a second. This chunk of material, known as a coronal mass ejection, or solar storm, together with the radiation and particles are what cause potentially large infrastructure failures on Earth.

How big can these events get? Looking at past records of solar activity doesn't help, because until the mid-19th Century we were not vulnerable to bad solar behaviour. Fortunately there is another possibility. We can observe flares taking place on other stars, and collect a lot of data.

Examination of stars of all types suggests our star may occasionally produce a flare much larger than the 1859 event. However, we can take some solace in knowing that humans and our ancestors have been wandering around on the Earth for maybe a million years or two, and living creatures for far longer. During that period there must have been periods of very bad solar behaviour, and we are still here.

Solar activity poses little if any direct threat to us. The danger comes from our increasing dependence on vulnerable technology.

It is unlikely we could ever totally avoid the effects of high level solar activity, but we know enough to predict what most of them would be, to prepare for them, and try to minimize the recovery time.

Maybe a key need is to reduce our dependence on vulnerable technologies. Maybe we'd actually enjoy a few days without the Internet. .

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• After sunset, Venus is very low in the southwest and Jupiter and Saturn low in the south.

• The Moon will be new on Oct. 6.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.