An Ocean of Air (35 page)

For decades after Birkeland's death, his theory remained in limbo. Even when the ionosphere was discovered and it should have been obvious that this was the conduit for Birkeland's currents to sweep over the sky, few scientists accepted his argument. Only in the 1960s was he finally vindicated. For this was now the space age, the time when satellites could penetrate the world that Birkeland had simulated and monitored, but could never touch. Satellites had discovered that space was radioactive. And they were also about to discover just how right Birkeland had always been.

***

MAY
1, 1958

James Van Allen was presenting his findings to the world. The patch of space hugging the top of our atmosphere was mysteriously radioactive. That's what
Explorers I
and
III
had clearly shown. He still wasn't exactly sure what this meant, or why it would prove to be important, but that hadn't prevented him from laying out the results to assembled scientists at the National Academy of Sciences. More difficult was explaining them to the journalists at the press conference that followed. Van Allen struggled to find the words. The radiation they had discovered seemed to congregate in a giant cloud, shaped like a doughnut with Earth occupying the hole in the middle. It was corpuscular radiation—that is, charged particles—girdling the planet in a giant, well ... something like..."Do you mean
like a belt?" one reporter demanded. "Yes, like a belt," Van Allen replied. And thus the "Van Allen belt" was born.

But there was still so much more to know. Where exactly did the radiation come from? How did it get trapped? What stopped it from continuing straight on down to Earth's surface? Van Allen already knew what he would do next to try to understand this. For as he hurried back to Iowa, he took with him a secret. Back in the spring he had received an extraordinary—and highly confidential—request. The army had decided to detonate nuclear bombs high in the air. Obviously it was vital that nobody knew. Their ostensible purpose was to see what might happen if, for example, the Russians did it first. They had frighteningly little idea of where the radiation from the bombs might go. But Van Allen's stock had skyrocketed along with his Explorer satellites. Would he help? Could he perhaps design a satellite that would monitor the radiation, and in the process learn a little about how his newfound belt worked?

Yes, of course he could. Van Allen and his team immediately began work on
Explorer IV.
They had only a few months before the tests were due, and the pressure was high. But the army superiors believed Van Allen's opinions on space instrumentation to be infallible. A string of engineers and officials were obliged to trek out to his small lab in the middle of Iowa throughout the summer to hear his opinions on their plans. He was amazingly pleasant, one remembered: "My most vivid memory of that visit was of a phone call he received from some important General while I was in his office. As I recall, his exact words were: 'Yes, General, I would be happy to come to Washington to testify for your project next week. However, one of my students is taking his oral exams then and I have to be here to help him.' From then on I looked on Van Allen as a voice of reason in a world gone mad."

Van Allen himself was calm about the whole affair: "Visitors to the University of Iowa ... were astonished to find that a crucial part of this massive undertaking had been entrusted to two graduate students and two part-time professors, working in a small, crowded basement laboratory of the 1909 Physics Building. But we knew our business, and were in no way intimidated."

On August 1, 1958, a ten-megaton bomb code-named Teak was exploded 47 miles above Johnston Atoll in the Central Pacific. Twelve days later came another, code-named Orange, and then three more at still higher altitudes.
Explorer IV
was there in the sky to see them all. She was the best satellite yet. A picture exists of Van Allen with her before launch, only the thinning crown of his head visible as he kisses her good-bye.

Explorer IV
saw exactly what Van Allen had hoped for. Though the lower-altitude explosions disappeared without trace, the high ones formed a new radiation belt, above the first. This had to be how the belts formed—by incoming radiation being trapped by the field lines, just as he had thought. This new belt was faint and feeble, though, and lasted only a few weeks before it drained away. It must have been humbling to see how little mankind's mightiest weapon could do, compared with the natural forces that were already somehow subjecting our planet to their relentless attack.

The Americans detonated a few more high-altitude nuclear bombs; so did the Russians. Mercifully all such explosions were banned by the treaty of 1967. But Van Allen now had something else to occupy him. On December 6, 1958, a new spacecraft,
Pioneer III,
left Cape Canaveral bound for the moon. On board was another of Van Allen's Geiger counters. For the newly born NASA, the mission was a bust. At about 63,000 miles above the surface,
Pioneer III
turned through a graceful arc and then tumbled back to Earth. But Van Allen was happy. The satellite had still gone farther than any man-made spacecraft before it, and in the process it had made another important discovery. There was not one Van Allen belt, but two.

The second, outer belt now had all Van Allen's attention. It was much higher—some ten thousand miles above Earth's surface, while the inner one was a mere four thousand miles up. It was also bigger, and the particles it contained were much more energetic. What had supplied the space above Earth with these two thick clouds of radioactivity? Had they come to us, as Birkeland had suspected, from the sun?

***

Today, fifty years after
Sputnik,
beeping satellites are almost ubiquitous in our skies. Some are for communications, some for military purposes, but
many were put there, like
Explorer I,
to tell us more about the most tenuous edges of Earth's atmosphere. The space above our planet has turned out to be far more complicated and strange than even Birkeland, with all his vision, had guessed. But it is astonishing how much he divined, from a vantage point fixed so far below.

He was right that cathode rays, or rather, electrons, do indeed come from the sun. In fact they appear in a continuous stream, which we now call the solar wind. The electrons aren't alone; they couldn't be. Negative charges repel one another, as do positive ones—only opposites attract. So a cloud of negatively charged electrons coming from the sun would spread out and disperse long before it could reach Earth. Instead the solar wind contains a mix of positive and negative particles—a plasma—which is flung off the wispy outer reaches of the sun's atmosphere at a temperature of 1,000,000 degrees. This solar wind blows constantly from the sun, in every direction. It breathes on comets to draw their long tails out behind them. It crashes continually against Earth's magnetic field, like a stream flowing past a rock, squeezing the field lines in the front and drawing the ones behind into a long tail that continues for hundreds of thousands of miles beyond Earth's backside.

But the serious emissions, the ones that cause Van Allen's belts and Birkeland's auroras, come from something more tempestuous still. Once in a while the sun hurls out a monstrous glob of plasma called a coronal mass ejection. Birkeland imagined the event, but he probably had no notion of its scale. A single outburst can easily contain a billion tons of glowing hot plasma moving at five times the speed of the solar wind. Nobody knows why the sun does this, though—also as Birkeland suspected—it is somehow associated with sunspots. What's certain is that with frightening regularity these deadly clouds come powering toward us, surfing on the shock waves of the solar wind.

The first place to feel one of these solar torpedoes is the outermost force field of our planet's arching magnetism. Out front, the lines of force press inward under the strain, but they do not buckle. Frustrated plasma streams around the planet's sides and then back, pressing up against the long magnetic tail that stretches far beyond the dark side of Earth. On it urges and squeezes until some plasma manages to barge past the magnetic sentinel and arrive inside the tail. By now, the plasma has long overshot Earth itself. But the field lines in the tail are now stretched almost beyond endurance; they snap like an elastic band, catapulting the plasma back toward us.

What happens next is a marvel. As fast as the plasma barrels back in toward Earth, more field lines gather it up and send its charged particles spiraling toward the poles like beads on a wire. And—just as Birkeland imagined—the electrons are then swallowed by the air of the ionosphere, which lights up with the effort to create the flickering lights of the auroras.

Small wonder people have feared the auroras for millennia; they are the outward sign of horrifying attacks from space. But those people who revered them are right, too, for they also show that our protective air is doing its job well.

Solar radiation plasma finds its way around the Earth's magnetic field
and into the long magnetotail, but is then directed to the planet's polar regions
where it is soaked up by the air or splashes out to create the Van Allen belts.

The Van Allen belts are an intricate part of this system. At first, Van Allen himself thought they were a "leaky bucket" that caught the plasma and held it until the bucket overflowed. We now know they are more of a splash screen. Plasma that is too energetic to be channeled to the poles and dealt with by the air instead bounces up into the outermost Van Allen belt. The field lines that arch some ten thousand miles above Earth hold these particles in suspended animation; they are unable to escape back into space or menace the ground, but leak harmlessly away and are replaced by new ones.

Birkeland would have been proud to know how right he was. He also would have enjoyed the pride of place he now holds on the Norwegian 200-kroner note. The front shows him with a typical half smile, wearing his smart suit and his round wire-rim glasses, though sadly not the red fez. On the left is a miniature sketch of a terrella, and behind him a stylized aurora. The back shows a geographic map of the Arctic, marking overhead the locations where satellites discovered flowing electrons in the sky. These are exactly what Birkeland predicted with his magnetic measurements, and they are now called Birkeland currents in his honor.

James Van Allen, meanwhile, became one of America's most famous scientists, appearing—among other illustrious places—on the cover of
Time
magazine. He also, of course, left his own name written in the sky in the radiation clouds that float over our heads. But he did even more than that. In 1973, while working in the clean-room of a satellite called
Pioneer
10,
Van Allen surreptitiously whipped off his white glove and planted a fingerprint on the spacecraft.
Pioneer
10
was the first man-made satellite to encounter Jupiter, and then Saturn. It continued on, to the outer reaches of the solar system, and beyond. By Van Allen's ninetieth birthday in 2004,
Pioneer
10
had traveled nearly 80 billion miles. He died, age ninety-one, in August 2006, but the satellite continues to coast silently into the deepest of deep space, heading for the red star Aldebaran, which forms the eye of Taurus, the Bull. The journey will take more than two million years, and Van Allen's fingerprint will go, too.

JUNE
16, 2006, 9:00
A.M.
TASIILAQ, EAST GREENLAND

"
THERE IT GOES.
" Local weatherman Søren Basbøll opens his fist to release the cable, and his weather balloon leaps eagerly upward. Within a few seconds we have to crane to see its tight white sphere outlined against the blue.

After almost a week of low clouds and flat white Arctic light, today has dawned unexpectedly clear and bright. At last we can see the tops of the mountains on the other side of the fjord. They are lined up with serrated sides and pointed summits, the way a child might draw a mountain range, and their flanks are still draped with snow. I know that beyond this first rank there are countless more, nothing but mountains, glaciers, and snow for 600 miles or more, and most of the peaks are unconquered and unknown.

In spite of the bright sunshine, the temperature is still below freezing and there is a stiff breeze. Søren retreats indoors to his coffee and computer, but I stay outside, watching the sky. The balloon is still visible, and if I squint, I can make out a gossamer cable below it that is trailing a small white box. Inside this box, instruments are gathering samples of Greenland's air. They are tasting and testing it. The numbers are already surfing back to ground on Marconi's radio waves: temperature, pressure, wind speed, and moisture, the meat and drink of the weather world.

I check my watch. By now Søren's balloon will have passed through the lowest part of our atmosphere, the part that means the most to the local Inuit hunters, and to the rest of the human race.