Skip to main content
Stars and solar physics

Stars and solar physics

What if a solar super-storm hit?

07 Aug 2014
Taken from the August 2014 issue of Physics World

Super-storms on the surface of the Sun are more than just an interesting oddity of astrophysics. As Ashley Dale explains, they can occur at any time and – if sufficiently strong – could cripple our modern way of life here on Earth

Powerful force


One September day in 1859, over the course of a few minutes, an event occurred that was to have spectacular consequences here on Earth. A sudden flash of brightness, known as a solar flare, had just erupted on the Sun, releasing about 1022 kJ of energy – equivalent to 10 billion Hiroshima bombs exploding at the same time. A massive coronal mass ejection (CME) hurled out about a trillion (1012) kilograms of charged particles at speeds of some 3000 km/s. As the material interacted with the Earth’s magnetosphere – the magnetic shield that usually protects us from high-energy charged particles from space – it triggered the largest ever “solar super-storm” on record.

Known as the Carrington Event – after the English astronomer Richard Carrington who spotted the flare – this super-storm saw the magnetic field around the Earth being stretched and torn apart. Accompanied by numerous sunspots, it led to the northern lights being seen as far south as the equator and created surges of energy that crippled the world’s electronics infrastructure.

Back in the mid-19th century, that infrastructure amounted to no more than about 200,000 km of telegraph lines and so the impact on the human population was relatively benign. But today’s world, which relies hugely on space technology and massively interconnected networks of power lines and fibre-optic cables, would be severely damaged if a Carrington-type event were to repeat itself. The consequences could be catastrophic and long-lasting.

In fact, it has now dawned on us – thanks to data from NASA’s Kepler mission, numerical modelling and the study of historical records – that the mood of our nearest star is far more hostile than we used to think. According to Jim Green, director of NASA’s planetary-science division, the Earth is, on average, in the path of Carrington-level events every 150 years – putting us five years overdue. Moreover, according to estimates made by Pete Riley, a heliophysicist at NASA and the US Department of Defense, the probability of another Carrington Event occurring within the next decade is as high as 12% (Space Weather 10 S02012).

In recent decades, we have already seen glimpses of the dangers that could lie in store. In March 1989, for example, a geomagnetic storm that was about a third of the strength of the Carrington Event caused an electricity grid operated by the Canadian firm Hydro-Québec to fail, triggering a nine-hour blackout for about six million people. Meanwhile, the “Halloween storm” of October 2003 – which was about half as intense as Carrington – disabled a number of satellites, destroyed a dozen transformers in South Africa and crippled a large section of its power systems. These events should have been a wake-up call, but little has been done about the potential threats. As the heliophysicist Pete Worden, director of NASA’s Ames Research Center, candidly puts it: “Space weather destroys stuff.” So what can be done?

SolarMAX is on the case

To help find answers, I was last year invited by the UK and European space agencies to take part in a 40-strong international, multidisciplinary task force of experts, led by Worden and Green. Over a period of six weeks, our group – dubbed SolarMAX – gathered at the International Space University in Strasbourg, France, to work out the risks from a solar super-storm to our modern way of life and to identify the best ways of limiting the potential damage. The result was a 100-page document to be disseminated to governments, space agencies and industry. You can read the full report online, although the human impact of a storm might be more apparent in my fictionalized account of the dramatic aftermath of such an event (see “Solar super-storms: a possible tale”, below).

It would be nice to pretend that everything will be fine in the event of a solar super-storm striking the Earth, but our findings were sobering. Severe disturbances to the Earth’s magnetic field would induce electric currents in the ground and overhead transmission lines – in fact, if the cables are long enough, the currents would be large enough to melt high-voltage AC transformers, which are critical components in all power grids. New transformers typically take up to a year to manufacture and install – and utility companies rarely keep backups as these devices cost at least $10m each. Any Carrington-level event would therefore generate widespread power outages that would last months, if not years, across most of the developed world, in particular North America and Europe. The lower latitudes of India and China, coupled to generally less conductive soil and more robust power infrastructures, means they would not be nearly as badly affected.

Without power, people would struggle to fuel their cars at petrol stations, get money from cash dispensers or pay online. Water and sewage systems would be affected too, meaning that health epidemics in urbanized areas would quickly take a grip, with diseases we thought we had left behind centuries ago soon returning. Worse still, most of the developed world works on a “just-in-time” philosophy, meaning that there is never more than two to three days’ worth of supplies available in urban areas at any given moment, be it food, fuel or medicine.

Nuclear power plants are another concern as they rarely have more than a week’s worth of backup power onsite to run their cooling systems. A switched-off reactor usually takes a month to cool down far enough to avoid a meltdown, which means that firms would find themselves fighting to get their hands on supplies of diesel fuel to operate those backup systems. With more than 300 nuclear power plants across North America and Europe, how many catastrophic meltdowns could be avoided? The relative vulnerability of the power grid across Europe to a solar super-storm coupled to the location of nuclear plants can be seen in figure 1, below.

Major disturbances to the ionosphere, caused by increased X-ray emissions from the Sun, would cause aircraft on the Earth’s dayside to lose their on-board navigation management systems and communications with the ground. Without air-traffic control, pilots would struggle to land their planes safely, while passengers, pilots and crew would receive much higher doses of cosmic radiation, which the Earth’s magnetic field and atmosphere together normally shields us from. Pilots, who are classified as radiation workers, typically fly above about 97% of our atmosphere – exposing them to an order of magnitude more radiation than people on the ground – but the increase in radiation dosage at such altitudes during a Carrington-like event would significantly threaten pilots’ and passengers’ health.

Satellites would be affected too, with the electrostatic discharges generated by geomagnetic storms frying electronics, damaging solar panels and confusing star-tracking orientation systems. The Earth’s atmosphere would also heat up and expand during such an event, increasing the drag on satellites in low Earth orbit and causing them to burn up on re-entry. Many TV broadcasts would cease, radios and mobile phones would not function, weather forecasts would end and defence systems would be made redundant.

Spacecraft that run satellite-navigation systems would either be lost entirely or produce data of limited use – hitting agriculture, surveying, oil drilling and timing. Our transportation-management infrastructure would grind to a halt, from air to sea. With more than 1000 operational satellites in orbit (costing an average of nearly $100m each), our space infrastructure could take a decade or more to recover. In fact, a study carried out in 2008 by the US National Research Council estimated that the satellite blackouts caused by space weather could cost upwards of $2 trillion in the first year alone. Meanwhile a separate 2013 study by insurance broker Lloyd’s of London and Atmospheric and Environmental Research, a climate and weather risk-management agency, estimated that the total collateral damage of a Carrington-level event on the world economy would amount to some $2.6 trillion.

Super-sized solutions

You might think I am scare-mongering, but the plain fact is that our reliance on electricity has made us extremely vulnerable to anything that could cut supplies. So to get a clearer idea of how often Carrington-level events are likely to occur, researchers at NASA are currently mining data from the Kepler space observatory. The mission was designed primarily to discover Earth-like planets orbiting other stars and has so far gathered data on more than 170,000 “main-sequence” stars in our galaxy. But by observing the variation in the luminosity of these stars over time, astronomers can spot and quantify the scale and likelihood of stellar super-storms.

Although only about 4% of the Kepler data has been scoured for super-storms, the work has shown that the Carrington event of 1859 really was nothing special. Preliminary estimates reveal that super-flares with an energy of 1024 kJ occur on the surface of stars just like our own once every 350 years, while those with energies of 1025 kJ take place every 800 years, and 1026 kJ flares every 3500 years. In contrast, an asteroid colliding with the Earth and creating as much collateral damage probably takes place only once every few thousand years. Policy-makers and politicians need to realize that super-flares are not just a threat, but inevitable.

Studying the Kepler data also gives us insights into how the properties of a star affect its volatility. For example, its rotation rate does not seem to alter the scale of super-flares produced, but the higher the rate, the more likely a super-flare event is to occur. The good news – if you can call it that – is that our star has a relatively low rotation rate. But we also need to get a better understanding of the Sun’s magnetic field and its weather because its field lines are intricately connected to those of each major body in the solar system. These lines in particular act as “channels” for solar wind to propagate along, triggering the formation of Van Allen belts – layers of plasma extending out to about 60,000 km beyond the Earth – and also “ring currents” carried by ions trapped in the magnetosphere. Both phenomena influence how solar weather generates solar super-storms so knowing more about them is vital (see “The nature of the Sun”, below).

The bottom line is that a deeper understanding of the Sun’s magnetic field and how it interacts with the Earth’s would help us obtain more accurate and longer-term forecasts of solar weather, as would a deeper knowledge of other solar mysteries, such as the origin of the Sun’s 11-year solar cycle, how sunspots form and why the surface of the Sun is so much cooler than the corona above. In fact, a sub-group of scientists in the SolarMAX project concluded that the best solution would be to send an array of 16 lunchbox-sized cube satellites into orbit around the Sun, located at about 45 million km from the Sun at their closest point and about 150 million km at their furthest. Such a mission would give us enough empirical data on the nature of the magnetic field between the Sun and the Earth with a high enough spatial resolution to help develop our understanding and therefore more accurate models for forecasting. The mission would also let us observe the Sun’s entire surface in almost real time, giving scientists the full picture of the surface when forecasting weather. And by splitting the satellite constellation into two elliptical orbits, tilted relatively, it would be possible to get a full 360° view in 3D of the surface features and solar phenomena. Right now we only ever look at the Sun from one side.

Current satellites give us no more than 15–30 minutes’ advance notice of imminent solar events and all have gone beyond their expected mission lives. Our proposed mission would let us make accurate forecasts – for up to a week into the future – of when, where and with what magnitude solar events will take place. Such forecasts would let us save the power grid by pre-emptively switching off vulnerable lines before a solar storm occurs. Planes could be grounded in time, satellites could be reoriented to limit damage, and national recovery programmes could be swung into action. Such warnings could also reduce the chance and expense of false alarms. What is more, we estimate that such a fleet of satellites would cost no more than $500m at today’s price – just 3% of NASA’s annual budget.

Smart ways forward

Another possible way of minimizing the potential disruption from space weather is to exploit the fact that many nations – at least in the developed world – are slowly updating their power transmission lines so that energy use can be measured at different points in the grid in real time via “smart meters”. This technology lets energy companies monitor and adjust performance to deliver power more efficiently in response to local changes in demand, but such information would be invaluable during major solar events. A real-time solar-weather response system would help to reduce the damage to the power grid by isolating vulnerable segments of the network from the rest of it to allow for smaller local failures rather than large inter-connected failures. The US is leading the way on this front – albeit in a small way – with a bill unanimously approved in 2010 to allocate $100m to developing protection for the bulk-power system and electric infrastructure from cybersecurity and solar-weather threats.

An accurate space-weather forecasting system would also help maximize the life expectancy of satellites by giving us time to manoeuvre them to minimize damage to solar panels. But future satellites need to be designed so that instruments vulnerable to sudden increases in radiation are better protected. The SolarMAX consortium examined some quite far-out ways of doing this, although it bugged me that there had to be simpler solutions to the problem. In fact, I quickly realized that engineers designing satellites and spacecraft had not thought much about simply optimizing the internal layouts of a craft so that sensitive, on-board instruments are shielded as well as possible from radiation.

It occurred to me that such equipment (and astronauts too for that matter) could be better protected simply by redistributing the existing internal architecture of a craft so that sensitive payloads are surrounded by non-sensitive bulk material such as polyethylene, aluminium and water. It would be a kind of “free lunch” because we would not need to make the craft heavier and so avoid making the mission more expensive; we would just need to rearrange what needs to be on board anyway. Not only would the craft be more likely to survive a major solar event, but it would also function for longer because prolonged exposure to radiation is essentially what kills off spacecraft in the long term.

After outlining my thinking to the group, I was allowed to pick a team of seven people – including Chunhui Wang, an “astronaut ergonomist” at the Astronaut Center of China – who together spent a few weeks exploring the potential advantages of my approach. We developed a case study based around a potential Mars mission that is currently being developed by the US-based Inspiration Mars Foundation, which wants to send a two-person manned probe on a Mars fly-by mission, reaching within 150 km of the red planet some time in the next decade. We worked with the foundation on its latest plans for the craft’s internal architecture and – by characterizing the radiation profile associated with its particular trajectory – were able to estimate the dose that astronauts flying to Mars might expect to receive. By redistributing the existing internal architecture of the spacecraft, we were able to cut the expected radiation dosage of the two-person crew by 15–20%. Though the radiation problem associated with space activities currently has no single solution, I saw this as a big win.

My proposal is just one of many practical – and feasible – solutions to the potential dangers of space weather. The risks are real. Solar super-storms are inevitable. Whether one affects civilization here on Earth is not a question of “if”, but “when”. However, damage can be averted with the technology we have today. The primary obstacle and danger lies not within the Sun, but with the ignorance of decision-makers concerning space weather: governments, industry and the public. As a species, we have never been more vulnerable to the volatile mood of our nearest star, but it is well within our ability, skill and expertise as humans to protect ourselves.


The nature of the Sun

What is the Sun made of?

All matter in the Sun is plasma: hot, ionized gas. Consisting mostly of protons, electrons and helium ions along with some oxygen and iron, this plasma moves across the surface like a deep and frothy ocean, circling the equator once every 25 days (at about 2 km/s) and once every 35 days near the poles. This rotation acts like a dynamo, producing the magnetic fields of the Sun. Over time, these field lines form vast channels, or “flux tubes”, on which the ionized gas is lifted up out of that fiery ocean in massive waves, leaving the Sun in a stream known as the solar wind.

What are sunspots?

The turbulence in the Sun’s superheated ocean, which is instigated by the differences in lateral rotation speed, makes the flux tubes gradually twist, break and reconnect with other lines beside them. These twisted and entangled magnetic field lines eventually inhibit the convection and effectively cut off the plasma flow in those channels, leading to a small but powerful local magnetic pole. Isolated from the circulatory system of the Sun, this pole gradually cools and forms a sunspot that can last for several days or weeks.

What about solar flares?

Magnetic field lines in the Sun’s corona – the aura of plasma encircling the Sun – contain lots of energy, which means that when the lines reconnect, lots of energy is released to create a huge explosion that we call a solar flare. Consisting of gamma rays, X-rays, protons and electrons, these flares are typically equivalent to 100 million Hiroshima bombs in terms of released energy.

How are coronal mass ejections created?

Occasionally, huge bubbles of plasma and magnetic field lines are ejected from the Sun over several hours in an event that is more energetic than any other in our solar system. Known as a coronal mass ejection (CME), such an event typically occurs after a solar flare, which means they are most common during a solar maximum (when the Sun is most active during its 11-year cycle). However the Carrington Event (see main text) occurred during a solar minimum, while not all solar flares cause CMEs and not all CMEs accompany solar flares.

How do CMEs affect us?

The Earth lies in the path of about 10% of all CMEs, with us typically getting hit eight minutes after a solar flare and anywhere between eight hours and three days after a CME, depending on their magnitude and trajectory. Like the Sun, the Earth also has a magnetic field originating from its molten core and how the two fields interact with the trajectory of a CME through the vacuum of space makes its path not at all simple.

What about Van Allen belts?

These are vast shells of plasma surrounding the Earth held in place by our own magnetic field. Disruptions to the Earth’s magnetic field through solar events affect the location of these shells, which can go some way to damaging the spacecraft they envelop. This plasma is delivered from the Sun via solar wind and any plasma lost from the Van Allen belts through disruption is quickly replenished.

And the ring current?

This is a doughnut-shaped region of mainly hydrogen, helium and oxygen ions surrounding the Earth’s equatorial plane. It shields the planet’s lower latitudes from electric fields induced in the magnetosphere. The waxing and waning of the ring current is a crucial element of our space weather as the process occasionally transfers charge from the surface of the Earth to satellites, potentially damaging them. Astronomers are not sure if these charged particles come from solar wind or our ionosphere – but better models of how particles are transported and accelerated between the Sun and the Earth would improve our understanding of the ring current.


Solar super-storms: a possible tale

Day 1 Andrew has just returned from work and is settling down for the evening in his London flat. Susan should be home late, flying back from a business trip to Quebec. Suddenly the TV and lights go off. Eggs sizzling in the frying pan gently fall silent. A power cut. Andrew fumbles for his phone and uses the torch app. He opens the curtains to find the street lights are out too; it’s dark as far as he can see. His neighbours are out on the street chuckling to each other, lit only by their phones. He goes to make a Facebook status update – no 4G. No signal? An early night then, after some eggs that are luckily just about cooked.

Day 2 Andrew wakes up at 5 a.m. to a siren wailing outside. He stumbles around for a glass of water. The taps aren’t working. There is only some barely cool white wine in the fridge. Susan still isn’t home. Opening his curtains again, he sees what looks like rush hour traffic despite the early hour. He spots at least a dozen helicopters over the city. This must be serious. Looks like a day off work! Andrew dresses and steps outside to buy food and drink from the local shop. The ATM machines are not working. He hardly has any cash. The shops are empty. The shopkeeper says something about space weather causing this. Space weather?

Day 3 Susan still isn’t home. Andrew hasn’t been able to find out if her flight landed. They have no way of contacting each other. The battery on his mobile phone has died, anyway. There are looters in the streets. He has limited food and his only water is in the toilet cistern. He leaves a note for Susan and drives out to his parents in the countryside. But the GPS is not working and he’s not sure of the way. It’s a two-hour drive in normal traffic and he only has half a tank of fuel. He knows the fuel pumps are not working. There may be road-blocks.

A week later Andrew reaches his parents on foot after his car was hijacked. They have a large water tank and a good supply of food, but looters abound. A solar super-storm has crippled the power and space infrastructure. Most of Europe and North America is floundering. Several nuclear power plants have suffered catastrophic meltdowns around the country. Diseases are spreading in the cities. China and India have not been too badly affected and are sending in troops and aid to help recovery.

A month later Things seem to be on the road to recovery. The water is running again but power is temperamental. Susan’s flight was diverted to Lyon, France, where she has been stranded since. The Chinese have been distributing food, water, medical and sanitation supplies. The government has begun to regain some level of order.

A year later Susan and Andrew have been back at work for a few months, though things have been slow to restart and the future of their jobs is now uncertain. Their insurance firm refuses to pay up for the damage looters did to their flat. Oil and gas prices have spiralled out of control, and there are going to be severe food shortages for some time. It will take years before certain conveniences return to normal. The geopolitical map has drastically changed. Many of their friends are looking to leave the UK and start new lives in the East.

Copyright © 2023 by IOP Publishing Ltd and individual contributors
bright-rec iop pub iop-science physcis connect