Table of Contents
Title Page
Copyright Page
Introduction
CHAPTER 1 - Target Earth: Asteroid and Comet Impacts
CHAPTER 2 - Sunburn
CHAPTER 3 - The Stellar Fury of Supernovae
CHAPTER 4 - Cosmic Blowtorches: Gamma-Ray Bursts
CHAPTER 5 - The Bottomless Pits of Black Holes
CHAPTER 6 - Alien Attack!
CHAPTER 7 - The Death of the Sun
CHAPTER 8 - Bright Lights, Big Galaxy
CHAPTER 9 - The End of Everything
EPILOGUE
Acknowledgements
Appendix
Index
VIKING
Published by the Penguin Group
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Penguin Books Ltd, Registered Offices: 80 Strand, London WC2R 0RL, England
First published in 2008 by Viking Penguin, a member of Penguin Group (USA) Inc.
Copyright © Philip Plait, 2008
All rights reserved
Library of Congress Cataloging-in-Publication Data
Plait, Philip C.
Death from the skies! : these are the ways the world will end / Philip Plait.
p. cm.
Includes index.
eISBN : 978-0-670-01997-7
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Introduction
THE UNIVERSE IS TRYING TO KILL YOU.
It’s nothing personal. It’s trying to kill me too. It’s trying to kill everybody.
And it doesn’t even have to try very hard.
The Universe is an incredibly hostile place for life. Virtually all of it is a vacuum, so that’s bad right from the start. Of the extremely few places that aren’t hard vacuum, most are too hot for chemical reactions to do very well—molecules get blasted apart before they can even properly form. Of the places that aren’t too hot, most are too cold—reactions happen too slowly to get interesting things to occur in the first place.
And in the very few places that aren’t in a vacuum, too hot, or too cold—and we really know of only one: Earth—all manner of dangers are lurking about. Volcanoes blast megatons of noxious chemicals into the air, spew lava for miles, and cause vast earthquakes. Tsunamis rewrite huge sections of coastlines. Ice ages come and go; mountains pop up and change the global weather system; whole continents get subducted into the glowing rock of the mantle.
And those are just the local problems. Earth still sits in the incredibly hostile environment of space, and all kinds of disasters might befall us from there—literally.
But then, that’s what this whole book is about.
Other job markets may lay claim to the title, but astronomy is actually the world’s oldest profession: early agricultural civilizations needed to know when to plant their crops and when to harvest, and the changing skies gave them their clues. The appearance of a certain constellation at a certain time was as good as marking a calendar.
The Sun was worshipped, and the Moon. This evolved into the belief that all gods lived in the sky. Studying the sky was tantamount to worship.
Astrology arose, attempting (and failing, I’ll note) to tie people’s lives to the sky. With the invention of the telescope, and cameras to fit onto them, the sky was found to be more than just a reflection of our superstitions. It became a canvas for some of the finest artwork humans have ever seen. Its vista boasted dusty, ribboned nebulae; sweeping, majestic galaxies; layered, mottled planets. It was a thing of beauty.
Astronomy became even more of a science, guided by principles of physics, mathematics, and chemistry. It blossomed into a field in its own right, and spawned many more.
And during all this time, through all those millennia, it was always assumed that the Universe was a place designed for humans. Everything must be just so to support us, and clearly this was the way things were meant to be.
Hubris. Silly, silly hubris.
Because the Universe is a violent place. Stars explode. Stars like the Sun can die in milder events, but die just the same. Whole galaxies collide, igniting fireworks on a cosmic scale. Asteroids impact other planets; could they hit us?
When we launched telescopes into space, we equipped them with cameras that could detect ultraviolet light, X-rays, super-high-energy gamma rays. We saw a Universe that seemed actively trying to destroy us. Exploding stars are phenomenally dangerous, blasting out vast amounts of killing force and energy. Black holes are everywhere, lurking throughout the galaxy, devouring anything that wanders too close. Flashes of high-energy light from distant points in the Universe whisper of powers terrible and gross, enough to fry entire solar systems that get in the way.
The Earth seemed to be the center of the Universe for much of mankind’s history. Now, however, the Earth seems fragile and impossibly small, a remote speck of dust lost in a Universe of frightening size and age.
In reality, the Universe cares not at all if we live or die. If a human were magically transported to any random spot in the cosmos, within seconds he’d die 99.999999999999999 percent of the time. At best.
Yet, despite all that (and quite a bit more still unsaid), here we are. Billions of years in, countless times around the Sun, sitting at the cross-hairs of dozens of cosmic weapons . . . our planet endures. Life not only survives, it thrives. Numerous setbacks have occurred, for sure, but life itself continues. As small and fragile and soft as humans are, we’ve managed so far.
Of course, we haven’t yet seen everything the Universe can unleash on us. A single asteroid impact could take out half of humanity without even breaking a sweat. A solar flare could wipe out our economy in seconds. And a nearby gamma-ray burst . . . well, that’s bad too. Very bad.
I love astronomy. I’ve devoted my entire life to it, to telling others about it, to writing about it. Astronomy is awe-inspiring, it’s beautiful, it provides philosophical perspective and holds the secret answers to so many of our most profound questions.
And I have no doubt whatsoever that astronomy can kill us. Well, no, that’s poorly phrased. Let me say that astronomical events can kill us. In some cases, our study of astronomy can actually save us. In others it provides us with inform
ation about what might kill us, though unfortunately without giving us any ideas of how to stop it.
And in many of those cases, there isn’t much we could do anyway.
This book is about those events. An asteroid impact killed the dinosaurs, and another rock may be out there with our name on it. The Sun seems constant, but is capable of doing serious damage. Supernovae wreak horrific destruction on epic scales. We’ll visit these scenarios, and many more. We’ll explore just what would happen if a black hole decided to pay us a visit, and what we can do as we ride out the eventual and inevitable death of the Sun, six billion years from now.
We’ll even have a front row seat as the Universe ages countless years, and see what happens at the end of time.
These topics have been written about before, of course. They are certainly the subjects of many breathless documentaries on TV. Most of these fall quite a bit short of reality; they exaggerate the damage, or underestimate it. They play up minor aspects and ignore major ones. They rarely, if ever, talk about the actual likelihood of such an event.
That last point is a critical one. Over the years I’ve written about astronomical disasters both real and imagined, and many people get honestly scared about them. Anytime an asteroid is predicted to pass by the Earth they envision an apocalyptic scenario, fueled by reporters who play up the danger without mentioning that the odds of our getting hit are less than the chance of winning the typical lottery. I’ve spent far too much time assuaging people’s fears, both rational and otherwise.
In this book, I won’t hold back. The reality of a nearby gamma-ray burst puts the sweatiest fundamentalist religion’s Armageddon prose to shame, dwarfing it to mundanity. I will go over, in loving detail, the Earth’s atmosphere ripped away, the oceans boiled, and all life sterilized down to the base of the crust.
But during all that, I will remind you that there is no star nearby capable of creating such a burst; and even if there were, the odds of it going off anytime soon are tiny; and even if it did, the odds of it being aimed our way are tinier yet.
But it’s still fun to think about “What if . . . ?”
While you’re reading this book, you may feel like you’re watching a horror movie at the theater: it’s fun, jolting, and maybe even terrifying. During the scary parts you may want to turn away, or hide your eyes, or spill your popcorn, but I’ll make sure the actual facts of the case are there to calm you down a bit afterward.
Of course (he says, chuckling low and with evil intent), there is a big difference: eventually the movie is over, you leave the theater, and you laugh at the scary ride.
You can’t do that in the real world. There are dangers out there, and we can’t avert our eyes from them. But as you read this book (I hope with your eyes open) you’ll learn just what the dangers are and, more important, what they aren’t. What horror movie is still scary once the lights are on?
And you always have to keep in mind that we’re still here. The Universe is a dangerous place, but again, we’ve gotten this far. We may just make it a while longer.
Or we may not. I have to be honest. The Universe is vast beyond imagining, and wields mighty forces. For nearly all the events depicted here, it’s not a matter of if, it’s a matter of when.
CHAPTER 1
Target Earth: Asteroid and Comet Impacts
THE ALARM WENT OFF AT 6:52 A.M. AS IT DID EVERY morning. Groggily, Mark slapped it off, then stumbled wearily to the bathroom. He splashed a bit of water on his face to accelerate the waking process, then began to brush his teeth.
Seeing that it was already a clear, warm day, he peered out the bathroom window to take in the scene as he brushed. The trees were covered in leaves, and flowers were in full bloom. The trees cast long shadows as the Sun slowly rose in the sky.
When he finished brushing, Mark noticed the odd silence. That’s funny, he thought. Why aren’t the birds chirping? From the corner of his eye he saw movement. Maybe it was an animal in the yard that had spooked the birds . . .
Stepping up to the window, he stood on tiptoe to look around the yard. What the—Every tree was casting two distinct shadows. His morning routine now forgotten, Mark watched in amazement as, for every tree, one of the shadows appeared to be moving, circling around the base of the tree like fast-motion video of a sundial. Nose pressed to the window, he looked up into the sky, straining to see what could be causing this strange display.
Suddenly, from under the eave, it appeared as if the Sun itself were streaking across the sky. Dazzled, Mark’s eyes took a moment to adjust, but it was still not clear what he was seeing. There was a disk of intense white light moving across the sky, faster than an airplane. Could it be a meteor?
It appeared to descend slowly to the horizon as he watched. Then, in the blink of an eye, there was a soundless but all-encompassing flash, so bright his eyes watered. He winced in pain. When he was able to look again, the small bright disk was gone, replaced by a much larger smear of light, fanning up from the horizon. The heat from the thing was palpable, even through the window. It was like standing near a fireplace. As the smudge in the sky expanded, Mark noticed something even odder: did the tops of the trees look funny? Was that smoke rising from them . . . ?
The heat became intense. It began to dawn on Mark that he might be in trouble. As he stood there wondering what to do, a sudden and sharp earthquake jolted the house, knocking him to the floor. It was over quickly, and as he stood up, dazed, he felt the heat more strongly than before as it poured through his now-broken bathroom window. He thought the worst was over, but what he didn’t know was that a wave of pure sound and fury tearing through the atmosphere was pounding toward him at 700 miles per hour.
Too late, he saw the face of the shock wave bearing down on him like a tsunami ten miles high. A mighty thunderclap swept over his burning house, pulverizing it to dust with Mark still inside, and the time for decisions was over.
Everything under this wave of sound was stomped flat. Trees that were ablaze a moment before from the heat of the explosion were snuffed out, then torn into millions of splinters. The expanding ring of pressure, already dozens of miles across, screamed past the location of Mark’s disintegrated house and continued moving, greedily consuming buildings, trees, cars, people.
Before it was over, the shock wave circled the Earth twice. Seismographs from around the globe registered the event as an earthquake of enormous scale, but no one paid attention to the scientific data for long. They were too busy struggling to survive.
METEORS AND METEOROIDS AND METEORITES, OH MY!
The Earth sits in a cosmic shooting gallery, and the Universe has us dead in its crosshairs.
Consider this: the Earth is pummeled by twenty to forty tons of meteors every single day. Over the course of a year, that’s easily enough to fill a six-story office building with cosmic junk.
While that sounds like a lot, it’s really only a pittance compared to the size of the Earth, which is about a quintillion—a million million million—times bigger. But space is swarming with debris, and the Earth is constantly plowing through it.
The vast majority of this material is detritus, tiny bits of rock that burn up readily in our atmosphere. When you go out on a dark, clear night, you see these as “shooting stars,” what astronomers call meteors. You might be surprised to find out that even the brightest ones you’re likely to see are caused by tiny bits of fluff called meteoroids, no bigger than a grain of salt. Something as small as a pea would make a fantastically bright meteor—I once saw one that was so bright it lit up the sky and even left an afterimage on my eye. I stood transfixed for the two or three seconds it took to flash across the sky, but was just as shocked when I later calculated that the rock itself was probably no bigger than a grapefruit.
How can something so small get so bright? There are two factors to consider. You may be familiar with the first: compressing air heats it up. Think about how warm a bicycle pump gets after you use it—when the air is squeezed inside the pu
mp, it gets hot and transfers that heat to the metal. You can actually burn yourself using a pump if you’re not careful. The more a gas is compressed, the hotter it gets. The second factor is the fantastic speed at which meteoroids travel. Most of them hit us at ten to twenty miles per second, and some come roaring in as fast as sixty miles per second! This is far, far faster than even a rifle bullet.
When something moving that rapidly enters our atmosphere, its velocity is translated into energy, which in turn is transferred to the air around it. As it screams through the upper atmosphere, a meteoroid rams the air violently—a rock moving at Mach 50 is going to compress the air a lot. The air gets squeezed so quickly and at such high pressure that it heats up thousands of degrees and starts to glow.
As you can imagine, all that hot air is like a blast furnace. The meteoroid, traveling just a few inches behind that rammed air, feels that heat. It can’t last long in those conditions, and if it’s small it usually burns up in a matter of seconds. We see a bright glow, a streak across the sky that lasts for a moment or two, and then it’s gone, adding its nearly insignificant mass to the Earth’s.
To a stunned observer, a meteor looks like it’s traveling just over his head, but in reality the action is occurring fifty or more miles above the ground. At that height the air is very thin, yet still thick enough to stop small, dense particles. But what if the particle is bigger than a pea, or a grape, or a watermelon? What if it’s the size of, say, a couch, a car, a bus?
For a bigger object, things are very different. If it’s a few yards across, instead of simply burning up, that chunk of space debris gets squeezed by the air pressure as if it’s in a vise—the pressure can top out at over a thousand pounds per square inch at meteoric speeds. This pressure can flatten out the incoming object in a process called pancaking for obvious reasons. But a rock can only take so much of that before it crumbles and falls apart. Within seconds, instead of one big rock coming in, we now have hundreds or thousands of little ones, all still moving at velocities of several miles per second, and all dumping their energy into the air around them. They compress further, fracture, heat up, and so on . . . and within a fraction of a second we have a whole lot of rubble releasing a whole lot of heat all at once.
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