DANA BERRY, SKYWORKS DIGITAL INC.
But asteroids aren’t the only threat. Comets are lovely, wondrous specters in the sky. Unlike asteroids, comets are like dirty snowballs: rock, gravel, and dust mixed in with ice holding it all together. When they get near the Sun, the ice melts.5 Many comets have pockets of ice under the surface, and when those sublimate the gas vents out in a jet. This acts like a rocket, pushing the comet around. If the comet is spinning—and most are—this means the comet will get pushed around randomly. That makes it extremely hard to accurately predict their orbits, and that much harder to land a rocket in them, or to use a gravity tug.
And it gets worse. The solar system looks something like a DVD seen edge-on: the planets orbit the Sun in the same plane. Asteroids too tend to stick to that plane. That means looking for them is a lot easier; we only need to keep checking the same parts of the sky.
But comets are wild cards. They aren’t confined to the solar system plane, and can come literally from any part of the sky. This can significantly cut into the lead time we have to do something about a killer comet approaching Earth. While we might have decades of notice for an asteroid impact, we might only have a few years for a comet. Even comet Hale-Bopp, which was one of the brightest ever seen, and which delighted hundreds of millions of people, was only discovered about two years in advance of its passage of Earth. Had it been aimed at us, there wouldn’t have been a damn thing we could have done about it. Hale-Bopp’s nucleus—the solid part of the comet—was twenty-five miles across. Had it hit, it would have made the asteroid impact that wiped out the dinosaurs look like a wet firecracker.
But even a small comet could have a disastrous, well, impact. Assuming it wasn’t confused for a sneak attack of some kind, the direct consequence of a small impact or Tunguska-like airburst over a city could lead to thousands of deaths and billions of dollars of damage. If it happened over a major city or economic landmark—New York City, California’s Central Valley (where much of the nation’s fruits and vegetables are grown), Tokyo—the results could be far worse. The good news is that long-period comets like Hale-Bopp represent less than a few percent of the overall impact hazard, and most short-period comets are easy to spot.
ODDS AND ENDS
So how big a danger are asteroid and comet impacts?
Statistically speaking, you’re not going to like the answer: the odds of getting hit are 100 percent. Yes, really. Given enough time, and if we do nothing about it, there will be impacts, and one will be big.
But the key part of that sentence is the “if we do nothing” part. The point is, we can do something. While the techniques described here sound like something out of a movie, they are all possible. Technically they’ll be tough, and they’ll be expensive. But the stakes are pretty high: global survival versus utter annihilation.
I think that given this, it’s about time we took these science-fiction ideas and made them science fact.
CHAPTER 2
Sunburn
IT’S JANUARY, THE DEAD OF WINTER ON THE NORTHERN hemisphere of Earth. During the short days, the Sun makes a desultory appearance low in the sky, only to sink below the horizon again a few short hours later. It can barely warm the planet, it seems. With the chill in the air, people don’t give the Sun a second thought. They wouldn’t even think it had much of an impact on their lives.
They’re about to be proven quite wrong.
The Sun is nursing a cosmic hangover. It has undergone some violent paroxysms over the past few years, erupting multiple times, sending tremendous blasts of matter and energy into space. Through sheer chance, these had mostly missed the Earth. The worst thing that had happened was one eruption nicking the Earth, causing beautiful aurorae at both poles, and disrupting some radio communications: an annoyance, but easily offset by the stunning display of northern and southern lights.
Things are on the decline now, and the Sun appears to be calming down. Scientists are just starting to think they can breathe easier.
They’re therefore caught by surprise when a vast group of sunspots peeks over the edge of the Sun. Sunspots are dark blotches of cooler material, caused by kinks and twists in the Sun’s magnetic field, and they are harbingers of solar activity. Scientists scramble to observe the sunspot group, bringing a fleet of ground-based and orbiting telescopes to bear on the star. They are greeted by an ugly sight: the Sun’s surface is gnarled, twisted, blackened, defaced by the spots. This group is a whopper, as big or bigger than the largest groups seen in 2003, which scientists still buzzed about.
For over a week astronomers nervously watch the active region, measuring its size, shape, and magnetic activity. The latter appears to have settled down, which could indicate either that the magnetic field is fading or that it is building up like a volcano.
They soon get their answer. The sunspots, normally dark, brighten tremendously in seconds, and stay bright for many minutes. At the same time, orbiting solar telescopes note wild magnetic fluctuations on the Sun, and minutes later are flooded with high-energy X- and gamma rays. Astronomers on the ground monitoring the orbiting observatories see unprecedented energy blasts, with measurements off the scale, when, suddenly, the data flow stops. Bewildered for a moment, they check their equipment, but then realize the problem is not on the ground, but in the sky: the huge influx of energy has fried their astronomical satellites.
Knowing that commercial satellites are at grave risk as well, the scientists make frantic calls to other observatories, but find the phones aren’t working either. Turning to their computers, they try e-mail, instant messaging, voice-over-Internet, anything, but communication is impossible. Nothing is working. Then their power goes out, and they realize things are about to get much worse.
Shortly after the flare, the Sun unleashes another blast, this time in the form of a brutal wave of subatomic particles. Traveling at phenomenal speed, the wave reaches the Earth, where it slams into and flows over the planet’s protective magnetic field. Submerged in the electromagnetic mayhem, satellite after satellite dies from an overdose of sunburn.
The effect reaches the ground as well. Transmission wires are suddenly overloaded with current, heating up, sagging, and snapping. Transformers are overwhelmed, exploding. Workers at electrical stations across the United States and Canada are snapped out of their routine and suddenly find themselves struggling valiantly and frantically to keep up with the cascading disaster, but it’s hopeless. Station after station goes down. Power goes out first to the U.S. Northeast, but within seconds the grid goes down in an expanding wave. Quebec, Boston, New York City, Philadelphia . . . minutes later, a hundred million people are without power at night in the dead of winter. They wake up the next morning to icy homes, without electricity, and with no means of finding out what happened.
Within hours, over half the planet is without power during one of the coldest winters in recent memory. Thousands die the first night, and many more follow over the next few weeks. The military jumps in, doing what it can to help those in need, but the sweep of the disaster is simply too broad. The number of deaths is staggering, an epic catastrophe on a scale unseen for a century. The economic impact alone is measured in the trillions of dollars, and entire nations go bankrupt.
Eventually, the Sun calms down. The active group of sunspots fades away. But magnetism on the Sun is fiercely complex. Within a few weeks, tangles and interconnections reappear in the solar magnetic field. Just as things on Earth start to settle, and people are able to bury the dead, another group of ugly sunspots begins to build on the star’s surface.
MY SUN, THE STAR
An occupational hazard of being an astronomer is getting free astronomy textbooks in the mail. Like e-mail spam (but tipping the scale at ten pounds), they come unannounced, and generally wind up in a used bookstore collecting dust (the real-world equivalent of the spam filter).
I can’t resist thumbing through them. I torture myself this way, knowing that I’ll find some odd chapter arrangement,
some scientific error, some small turn of phrase that will irk me in some way. And always, without fail, I find it in the section about the Sun. Invariably, there will be some permutation of this sentence: “The Sun is an ordinary, average star.”
If you decide to read only this chapter and then close this book forever, then please walk away with just one thing: the Sun is a star, with all that this implies. The Sun is a mighty, vast, furiously seething cauldron of mass and energy. The fires in its core dwarf into microscopic insignificance all the nuclear weapons ever built by mankind. A million Earths would be needed to fill its volume, and the light it emits can be seen for trillions upon trillions of miles. Invisible forces writhe and wrestle for control on its surface, and when it loses its temper, the consequences can be dire and even lethal.
That is what it means to be an “ordinary” star.
Let’s be clear—there are lots of stars like the Sun, and if you phrase it carefully, then sure, the Sun is average. The smallest stars have roughly one-tenth its mass, and the largest have a hundred times its mass, so the Sun is somewhere near the low end of the range. But this neglects the actual population of stars: low-mass stars are far, far more common than their hefty brethren. More than 80 percent of the stars in our galaxy are lower-mass than the Sun. Roughly 10 percent have the same mass as the Sun, and 10 percent have more. So really, in a standardized cosmic test, the Sun scores pretty well. Maybe a B+.
Of course astronomers—and I count myself guilty here as well—do love to use diminutive adjectives when describing low-mass stars: dinky, tiny, feeble. But that’s hardly fair, either: even the smallest star is far, far larger than Jupiter, and Jupiter is pretty big; three hundred Earths would fit inside it, so even a small star is a huge object.
And yet the Sun is larger in size than the majority of stars in the galaxy: their median diameter is about a tenth that of the Sun. So even on a cosmic scale the Sun is big.
On a human scale, as you can imagine, it’s a scary, scary place.
The Sun is about 93 million miles away. If you could build a highway and drive there, it would take over 170 years. Even an airplane would take two decades to fly to the Sun if it could.
And yet . . . imagine it’s summer and you’re standing outside. You turn your face up to the Sun. Feel the warmth? Sure! The Sun is so bright you can’t even look at it. And if you stand there for more than a few minutes you risk damaging your skin.
The Sun’s fearsome power is generated deep in its core, where a controlled nuclear reaction is taking place: the Sun is continuously fusing nuclei of hydrogen together to create helium nuclei. Every time this reaction occurs a little bit of energy is given off, and in the Sun’s core the reaction happens a lot: every second of every day, the Sun converts 700 million tons of hydrogen into 695 million tons of helium.
The missing 5 million tons get converted into energy, via Einstein’s famous equation E = mc2, which shows that mass and energy can be converted back and forth into one another, and that a tiny bit of matter produces a whopping amount of energy. Five million tons is a huge amount of matter, the equivalent weight of seven fully loaded oil supertankers . . . and the Sun chews through that much hydrogen every second.6
The energy created every second in the core of the Sun—equal to the energy it emits from its surface—is the equivalent to the detonation of 100 billion one-megaton nuclear bombs. This is 200 million times the total explosive yield of every nuclear weapon ever detonated on, below, and above the surface of the Earth . . . and the Sun does this every second of every day, and will continue to do so for billions of years yet to come.
Some people like to say the Sun is essentially a giant nuclear bomb, but that’s misleading: a bomb explodes.7 But the Sun doesn’t explode, because it has a lot of mass. This means it has a lot of gravity, which balances the energy it generates. The heat produced makes the Sun want to expand (like a hot-air balloon expands), but the Sun’s own gravity holds it together. It’s a balancing act; in fact, a good definition of a star is a ball of gas with nuclear fusion in its center held together by its own gravity.
But just because the entire Sun doesn’t explode like a bomb doesn’t mean that explosions don’t happen. In fact, the Sun is capable of epic eruptions; but they’re not nuclear in nature, they’re magnetic.
CURRENT EVENTS
When I was a kid (and sure, I’ll admit it: even today), I was fascinated by magnets. I had a few different kinds, and I would play with them constantly. I read a lot about magnetism, and in one of my books it said magnetism could be destroyed by heat. I (carefully!) held a bar magnet in a candle flame for a few minutes, and sure enough, after that it wouldn’t attract nails or needles anymore.
I was also something of an astronomy geek even then, and I had a book that talked about the magnetic field of the Sun. I remember being confused by this: how could the Sun have a magnetic field if it was so hot?
What I didn’t understand is that there is more than one way to create a magnetic field. Simply put, a magnetic field can be generated by moving electrical charges. When you turn on a light, for example, electrons (subatomic particles with a negative charge) flow through a wire from the wall to the light. This motion produces a local (temporary) magnetic field around the wire. When you turn off the light, though, the flow of electrons stops, and the magnetic field collapses.8
This has a very interesting—and useful—effect. If an electrically conductive object like a wire moves through a magnetic field, an electric current will flow along the wire. This current, in turn, generates its own magnetic field. If the current moves in just the right way, its magnetic field will reinforce the magnetic field already there and you get a self-sustaining system.
However, this only works if there is an outside source of energy to make things move. For example, you could use a crank to make a coil of copper wires rotate inside a magnetic field (generated by a permanent magnet). Your arm supplies the outside energy. Or, if you’re smart, and you want to make a lot of electricity, you stick this getup near a source of flowing water—say, inside a dam—and make giant turbines composed of copper that spin as water flows past them . . . which is precisely how hydroelectric power plants work. A system that converts mechanical energy to electromagnetism in this way is called a dynamo.
The Sun is just such a dynamo. Its interior is hot: so hot, in fact, that electrons are stripped off their atoms, allowing them to flow more or less freely. An atom that is missing one or more electrons is said to be ionized. As these electrons move in the ionized gas, they generate magnetic fields.
If the Sun were just sitting there in space, a nonmoving and non-rotating ball of hot gas, the electrons inside would move around higgledy-piggledy, and all those individual magnetic fields generated would be oriented in random directions and cancel each other out. But the motions of the electrons in the Sun are far from random. For one thing, the Sun spins on its axis once a month, and that can create streams of gas in its interior. This preferred direction of motion for the electrons means that their individual magnetic fields can build on one another like creeks all flowing into a river, creating a larger magnetic field.
If it were just that simple, scientists would understand everything about how the Sun works. But in reality the Sun is incredibly complicated, with a vast system of moving gas inside it. The heat from the core makes gas above it rise,9 generating towering conveyor belts of gas over 100,000 miles high, moving up and down inside the Sun. Other rivers of gas move around it like the jet stream does on Earth, and yet another set of streams flows north and south as well. When taken all together, the Sun more closely resembles a ball of writhing worms than a simple sphere of gas. It’s like a street map of Tokyo, but in three dimensions and changing with time as well. Because of this, the magnetic field of the Sun is a nightmare as well, making it ferociously difficult to understand. On the positive side, though, it also keeps a lot of solar physicists off the streets.
All of this together is what creates the
Sun’s dynamo. The charged particles inside the Sun are moving in currents. These currents move inside a magnetic field, so the currents themselves generate a magnetic field, and the whole thing is self-reinforcing. The crank, in this case, is the Sun itself, with its own rotation providing the mechanical input energy needed to generate the dynamo. The Sun is huge and massive, so there is a vast amount of rotational energy to tap into. The solar magnetic field is created at the cost of the Sun’s spin, but it will take billions of years for the energy loss to result in a noticeably slower spin.
The Sun’s magnetic field is complicated and interesting, and by interesting, of course, I mean dangerous.
Or had you forgotten the title of this book?
MAGNETIC BUBBLE, COIL AND TROUBLE
Earlier, I mentioned that a star can be defined as an object with fusion in its center, whose tendency to expand due to energy production is balanced by its gravity.
Stars are a study in balance in this way. If gravity were weaker, they’d expand or explode. If their energy generation were a little weaker, they’d shrink or collapse (more about both of these in later chapters). Their rotation, chemical composition, gravity, heat, pressure, and yes, magnetic field all combine in exquisite balance to produce a stable star.
But sometimes things get out of whack.
When a simple magnetic field is illustrated, you usually see a set of lines emerging from the poles of the magnet, connecting one pole to the other. The field lines of a bar magnet, for example, look something like a doughnut. These magnetic field lines are useful to visualize the strength of a magnet: where the lines are bunched up together (like near the poles of a bar magnet), the magnetic field is stronger; where they are spaced out the field is weaker. If you place a small bar magnet inside the magnetic field of a larger magnet, the smaller one will align itself along the larger’s field lines. That’s why a compass points north; the needle is a magnet, and it aligns itself along the Earth’s magnetic field lines.
Death From the Skies!: These Are the Ways the World Will End... Page 4