he fateful day began like any other, but as the morning dragged on I began to notice a peculiar silence. I'd been expecting a call or two on my cell phone that hadn't materialized, and when I tried to call out to discover why, I found my phone ... malfunctioning. Not dead, but definitely not working properly. The horror! I turned it on and off a few times, but succeeded only in changing the symptoms. And suddenly it dawned on me: Those astronomy headlines were not a scientific curiosity, but an actual event of cosmic proportions, unfolding all around me. I was a personal victim, like millions of other people around the world, of that ancient scourge of the spaceways: sunspots.
OK, they're more of an inconvenience than an actual scourge—nobody got hurt or anything—but according to evidence from polar ice cores, last month's solar storms may have been the worst to hit Earth in a thousand years. When the northern lights reach all the way down to Texas, you know something's up! Cell phones weren't the only radio traffic to suffer; commercial fishing boats and other long-range communicators were cut off completely. Our power grids (like they didn't have enough trouble already) suffered a plague of equipment-munching spikes and ripples. The worst damage struck 23,000 miles above Japan, where two unmanned communications satellites—valued at hundreds of millions of dollars apiece—were struck by crippling blasts of radiation and fell forever silent.
Imagine it if you will: the Earth beneath your feet, a rock some 7,500 miles thick, wrapped in a 20-mile blanket of atmosphere and a 40,000-mile magnetic umbrella that is struck by 10 charged particles from the solar wind per square centimeter, every second of every day. That's in the quiet times; in a G5 proton storm this figure soars to a dizzying 100,000 particles. Thanks to Earth's magnetic field, though, few of these particles strike the planet broadside; most are deflected away, and the rest are trapped in magnetic field lines and spiral in toward the north and south poles, screaming out radio static as they fall. And when these hot particles finally slap into the cold polar air, molecules in the upper atmosphere are excited until, like a world-sized neon light, they begin to glow.
The restless, shifting patterns of the aurora borealis are an echo of the distant spasms of the sun itself. Our parent star—known to astronomers as Sol—looks quiet enough in the sky, as peaceful and constant as anything the human world has to offer. But let's face it: The thing is a thermonuclear bomb that's been exploding for 4 billion years and will keep on exploding for another 5 or 6 billion. Its surface goes through quiet and noisy phases in a steady 11-year cycle, but the underlying process—nuclear fusion in the dense, superhot stellar core—never sleeps.
Here comes the sunspot
Why sunspots? On hazy days these dark patches have been observed on the sun since ancient times, and were first explored telescopically in 1600, just in time for the 1645-1715 "Mandauer minimum," a 50-year period during which no sunspots were observed at all, and which may have played a role in Earth's "little ice age" from 1550 to 1850. The spots' 11-year waxing and waning was mapped in the first half of the 19th century, and though a complete understanding of their workings eludes us even today, we do know that they're magnetic anomalies on the sun's vaporous "surface"—cold-weather fronts where the usual 5,800-degree temperatures plummet to a frigid 3,000. If this sounds minor, consider that an equivalent change on Earth would freeze our oceans straight through, with a heavy snow of carbon dioxide settling down from a sky as dry as the moon.
Plasma is a sort of gas that is hot enough to evaporate or "ionize" electrons right off their parent atoms, and the sun is a huge, hot ball of this stuff, with no solid core. (Far larger than Jupiter, the core is six times denser than Earth's own center of molten iron, but so hot that it can't form a solid, or even a liquid.) This allows the sun's equator to rotate faster than its poles (a 25-day rate vs. 29 days for the higher latitudes). This differential rotation—like the swirling molten iron in Earth's interior and the spiraling electrons in the coil of an electromagnet—generates an enormous magnetic field. Meanwhile, the roiling "convection cells" of the solar interior generate smaller fields that bend and twist around each other in a chaotic mess.
Sometimes, these disturbances form loops that rise right up through the sun's surface, like bubbles in a pot of boiling soup. Where the ring shape of a magnetic loop just touches the white-hot photosphere—the "surface" of the sun—you get a region where the movement of plasma is suppressed, and the transport of heat from the stellar interior slows down. Thus, the area cools off and becomes dimmer; a sunspot is born. Then, as the loop continues to rise, the spot breaks into two pieces, like the north and south poles of a horseshoe magnet, and the arch that connects them carries up a swirling cloud of plasma called a solar prominence.
These prominences—which can be many times larger than the planet you're sitting on—sometimes linger for a few days and often subside, but occasionally their rise is fast enough to burst the top of the magnetic bubble. When this happens, the plasma breaks free, and huge numbers of protons and electrons are ejected violently into space at up to 1,500 kilometers per second (0.5 percent of the speed of light) in an event known as a solar flare.
A flare for the future
Flares don't travel in straight lines, but spiral outward along the magnetic field of the rotating sun. Usually they pass harmlessly through the solar system and out into interstellar space, but occasionally the Earth gets in the way, and a geomagnetic storm results. These "space weather" events are tracked and predicted by NOAA, the National Oceanic and Atmospheric Administration, which rates them on a scale from G1 to G5, and the resulting radio blackouts from R1 to R5. Flares themselves are measured by their X-ray output on a scale of X1 to X20, but last month's storms buried the needle on all three scales, swamping the measuring instruments. NOAA officials confess they can only guess at the largest storm's true power, which may have gone as high as X40. Wow.
At this point, an alarmist might reasonably wonder whether this unprecedented activity bodes ill for civilization, the human race or even the planet Earth itself. Are we in danger? Thankfully, the answer is no. An astronaut caught in interplanetary space could easily suffer a lethal radiation dose from even one of these flares, but a properly designed spaceship would use the onboard fuel and water tanks as an effective shield, and could also dangle strong magnets from its sunward face to help push the radiation aside. Here on Earth we're even better protected by our thick atmosphere and strong magnetic field, and while high-flying aircraft at high latitudes can absorb the equivalent of several hundred chest X-rays, this is still negligible in terms of its health effects.
And no, the sun itself isn't going to blow up. In fact, it's going to start quieting down soon for another 11-year slumber. There are stars that shed large amounts of mass in a type of cataclysmic explosion called a nova, and still others that disintegrate completely in an even bigger explosion: a supernova. But those are different types of stars, much heavier than ours. Sol belongs to the G2 spectral class, and while it won't last forever its eventual fate is much gentler than a simple kaboom.
The sun's actual energy production takes place in its core, where temperatures of 15 million degrees are hot enough to ram atomic nuclei together against the electrical repulsion that ordinarily holds them apart. Here, hydrogen nuclei are fused together in groups of four to become helium nuclei, and since helium is heavier than hydrogen, it tends to remain in the core, which consequently grows larger and denser and hotter over time. Indeed, the heat output of the sun increases by about 10 percent every billion years as the fusion layer inches closer to the surface, and eventually this heating will overcome the force of gravity, and the sun will swell into a "red giant" whose edges will subsume the Earth and eventually extend well past the orbit of Mars. With any luck, the human race will have moved to someplace cooler by this time, or evolved into pure-energy superbeings for whom a stellar interior is just a gigantic ball of food.
In any case, Sol will gradually exhaust its fuel supply and then, with a sigh of escaping gas, shrink into a hot, solid, Earth-sized sphere called a white dwarf. The great bomb in the sky falls silent at last. Over tens of billions of years, the white dwarf will eventually cool off and become a black dwarf—a ball of superdense iron surrounded by a crust of lighter elements. The surface gravity on this world will be a whopping 100 million times greater than Earth's, and its remaining energy will gradually escape into space. Red heat will fade to room temperature, and finally to the 3-Kelvin background temperature of the cosmos itself, where any remaining hydrogen will turn to metal, and the last wispy traces of helium will form a liquid ocean that should linger until the end of time.
Once again, the energy creatures will have to adapt or relocate. Or die, yes, but I prefer to think they'll choose life, and perhaps even look back fondly on the days when they yakked on cell phones under the rays of a burning sun, dreamily counting the spots.
Wil McCarthy is a rocket guidance engineer, robot designer, science-fiction author and occasional aquanaut. He has contributed to three interplanetary spacecraft, five communication and weather satellites, a line of landmine-clearing robots and some other "really cool stuff" he can't tell us about. His short writings have graced the pages of Analog, Asimov's, Wired, Nature and other major publications, and his book-length works include the New York Times notable Bloom, The Collapsium and most recently The Wellstone and a related nonfiction book, Hacking Matter.
