On Thursday, September 1, 1859, a 33-year-old brewer and amateur astronomer named Richard Carrington climbed the stairs to his private observatory near London, opened the dome slit, and as was his habit on a sunny morning, adjusted his telescope to project an 11-inch image of the sun onto a screen. He was tracing sunspots on a piece of paper when, before his eyes, “two patches of intensely bright and white light” suddenly appeared amid one large sunspot group. At the same time the magnetometer needle dangling from a silk thread at London’s Kew Observatory began dancing wildly. Before dawn the next day enormous auroral displays of red, green, and purple illuminated the skies as far south as Hawaii and Panama. Campers in the Rocky Mountains, mistaking the aurora for sunrise, got up and started cooking breakfast.
The flare Carrington had observed heralded a solar superstorm—an enormous electromagnetic outburst that sent billions of tons of charged particles hurtling toward Earth. (Another amateur English astronomer named Richard Hodgson also witnessed the flare.) When the invisible wave collided with the planet’s magnetic field, it caused electrical currents to surge through telegraph lines. The blast knocked out service at several stations, but telegraphers elsewhere found that they could disconnect their batteries and resume operations using the geomagnetic electricity alone. “We are working with the current from the Aurora Borealis alone,” a Boston telegrapher messaged an operator in Portland, Maine. “How do you receive my writing?”
“Much better than with the batteries on,” Portland replied.
Operators of today’s communication systems and power grids would be less sanguine. No solar superstorm as powerful as the 1859 event has occurred since, so it is difficult to calculate what impact a comparable storm might have on today’s more wired world. A hint came with the Quebec blackout of March 13, 1989, when a solar storm roughly a third less powerful than the Carrington event knocked out the power grid serving more than six million customers in less than two minutes’ time. A Carrington-class storm could fry more transformers than the power companies keep stockpiled, leaving millions without light, potable water, sewage treatment, heating, air-conditioning, fuel, telephone service, or perishable food and medications during the months it would take to manufacture and install new transformers. A recent National Academy of Sciences report estimates that such a storm could wreak the economic disruption of 20 Katrina-class hurricanes, costing one to two trillion dollars in the first year alone and taking a decade to recover from.
“We cannot predict what the sun will do more than a few days ahead of time,” laments Karel Schrijver of Lockheed Martin’s Solar and Astrophysics Laboratory in Palo Alto, California. With a period of maximum solar activity expected to begin this year, space-weather centers are adding staff and hoping for the best. “We’re trying to understand how space weather percolates into society and just how bad it can get,” says Schrijver. “The morally right thing to do once you’ve identified a threat of this magnitude is to be prepared. It’s like earthquakes in San Francisco. Not preparing for it has intolerable consequences.”
Few objects seem as familiar as the sun—there it is, up in the sky every sunny day—yet few are so strange. Look through a solar telescope, and the quotidian yellow disk is transformed into a dynamic wonderland, where planet-size prominences rise into black space like glowing jellyfish, only to loop and slither back hours or days later, as if enthralled by some unseen force.
As indeed they are. Neither solid, liquid, nor gas, the sun is made up of plasma, the “fourth state of matter,” which forms when atoms are stripped down to naked protons and electrons. All those charged particles make the solar plasma a splendid conductor of electricity—much more conductive than copper wire. The sun is also packed with magnetic fields. Most remain buried inside the sun’s massive girth, but some magnetic pipes, as thick as the Earth is wide, emerge on the surface as sunspots. This magnetism choreographs the slithery dance in the sun’s atmosphere and powers the solar wind, flinging outward a million tons of plasma every second at a million miles an hour.
Driving all this activity is the intriguingly intricate machinery of an unexceptional star. The sun’s core—a seething, 27-million-degree-Fahrenheit plasma spheroid six times as dense as gold—fuses 700 million tons of protons into helium nuclei every second, releasing the energy of ten billion hydrogen bombs in the process. The core throbs gently, expanding when fusion rates climb and contracting when they damp down. Superimposed on this slow, deep heartbeat are myriad other rhythms, ranging from an 11-year sunspot cycle to rhythms spanning centuries.
The energy produced by the fusion in the sun’s core is carried outward by high-energy photons as they ricochet through a dense maze of ions and electrons. Matter is so tightly packed in this radiation zone that it takes more than 100,000 years for the photons to emerge into the surrounding convection zone, 70 percent of the way out from the solar center. After a month or so more, the photons emerge into the photosphere, the part of the sun that we see. From there, it takes a mere eight minutes for them to reach Earth as sunlight.
As one might expect, this titanic thermonuclear furnace makes a lot of noise. “The sun rings like a bell in millions of distinct tones,” notes Mark Miesch of the National Center for Atmospheric Research in Boulder, Colorado. The tones generate ripples on the solar surface, which scientists study to map currents deep in the convection zone, a discipline called helioseismology. Information conveyed by helioseismic sensors aboard NASA’s Solar Dynamics Observatory satellite recently enabled Stanford University researchers to detect magnetic bundles 40,000 miles below the solar surface and to predict their emergence, days later, as sunspots.
Such data provide crucial information on how solar storms form. The sun functions as a gigantic dynamo, with global magnetic field lines encircling it from pole to pole like a birdcage. Local field lines, entangled with plasma in the convection zone, twist and kink and poke through the surface, forming loops made visible by the hot, glowing plasma. When loops cross, they can essentially short-circuit, causing the tremendous plasma explosions called solar flares. Such flares release the energy equivalent of hundreds of millions of megatons of TNT, spewing x-rays and gamma rays into space and accelerating charged particles to nearly the velocity of light.
The Carrington event consisted of a powerful solar flare that produced the second of a rare pair of coronal mass ejections (CMEs)—gigantic magnetic eruptions of heated plasma belched into space. The first CME probably reached Earth in a normal span of 40 to 60 hours, clearing a path through the solar wind for the second one to make the trip in a mere 17 hours. Their combined impact squashed the Earth’s magnetosphere—where the planet’s magnetic field interacts with the solar wind—down from its normal altitude of 40,000 miles to 4,000 miles, temporarily eliminating the Van Allen radiation belts girdling the planet. Charged particles entering the upper atmosphere set off intense auroras over much of the Earth. Some people thought their cities had caught fire.
A Carrington-class superstorm probably occurs only once in several centuries. But even storms of much smaller magnitude can cause considerable damage, especially as humans become increasingly dependent on technology deployed in space. Solar storms disrupt the ionosphere—the layer of Earth’s atmosphere where auroras occur, more than 60 miles above the Earth’s surface. The pilots of the nearly 11,000 commercial flights routed over the north polar region each year rely on shortwave radio signals bouncing off the ionosphere to communicate above 80 degrees of latitude, beyond the range of communications satellites orbiting over the Equator. When space weather disrupts the ionosphere and interrupts shortwave communications, pilots are obliged to change course, which can cost $100,000 a flight. A flustered ionosphere deranges GPS signals as well, resulting in positioning errors that can be more than 150 feet. This means that surveyors must pack up and go home, floating oil-drilling rigs have trouble remaining on station, and pilots cannot rely on the increasingly popular GPS-based systems employed for landing at many airfields.
UV light emitted during solar flares can also disturb satellite orbits by heating up the atmosphere, which increases drag. NASA estimates that the International Space Station descends more than a thousand feet a day when the sun is acting up. Solar storms could also affect the electronics on communications satellites, turning them into “zombiesats,” adrift in orbit and dead to the world.
Unlike satellites in space, most power grids have no built-in protection against the onslaught of a powerful geomagnetic storm. Since large transformers are grounded to the Earth, geomagnetic storms can induce currents that could cause them to overheat, catch fire, or explode. The damage could be catastrophic. According to John Kappenman of Storm Analysis Consultants, who studies the impact of space weather on the electrical grid, a solar storm like one that took place in May 1921 would today turn out the lights over half of North America. One on the order of the 1859 event could take out the entire grid, sending hundreds of millions of people back to a preelectric way of life for weeks or perhaps months on end. In Kappenman’s words, we’re “playing Russian roulette with the sun.”
At least we’re not playing blindfolded. In 1859 the world had few tools for studying the sun, beyond telescopes and a handful of magnetic monitoring stations. Today scientists constantly monitor our home star with an imposing armada of satellites that can take images in x-ray and ultraviolet wavelengths blocked by Earth’s atmosphere. The venerable ACE (Advanced Composition Explorer) spacecraft, launched in August 1997 and still going strong, monitors the solar wind from an orbit around the L1 libration point, a stable gravitational spot located a million miles sunward of the Earth. SOHO, the Solar and Heliospheric Observatory, carries a dozen detectors that record everything from high-speed solar-wind protons to low-speed solar oscillations. STEREO consists of a pair of satellites, one preceding and the other trailing Earth in its orbit, that together take 3-D solar images revealing how coronal mass ejections loft off the sun’s surface and speed out through space. Meanwhile the Solar Dynamics Observatory, launched into a geosynchronous orbit in February 2010, downloads 1.5 terabytes of data every day on the sun’s atmosphere, oscillations, and magnetic field.
Yet much remains to be done. “Space weather is where terrestrial weather was 50 years ago,” says physicist Douglas Biesecker of NOAA’s Space Weather Prediction Center in Boulder, Colorado. Because the impact of a storm depends in part on how its magnetic field aligns with that of the Earth, scientists cannot be sure of the storm’s intensity until it reaches the ACE satellite—sometimes a mere 20 minutes before it slams into Earth.
So researchers concentrate on forecasting a storm’s potential strength and its likely arrival time, giving vulnerable systems time to prepare. Last October the NOAA group inaugurated a new computer model, called Enlil after the Sumerian god of winds, that can predict when a CME will hit Earth, plus or minus six hours—twice as accurate as previous forecasts. The modeling is complex, in part because CMEs can interact strongly with the normal solar wind, making their progress as unpredictable as that of a running back through a defensive line. The uncertainties notwithstanding, Enlil’s forecast for the arrival of a potentially major storm on March 8 of this year was off by a mere 45 minutes. That storm turned out to be a bit of a dud. We may not be so lucky next time.
“We haven’t seen anything big in this solar cycle yet,” says Biesecker. “But now we know that when the big one comes, we’ll be able to nail it.”