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Authors: Ph. D. Philip Plait

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An innovative idea in asteroid impact mitigation is to use the gravity of a small spacecraft to move a hazardous asteroid out of harm’s way. Given enough lead time, this is a very precise method of altering an asteroid’s orbit.
But of course there are technical difficulties with this method too; there always are. The rocket cannot fire straight down, toward the asteroid, because it will push the asteroid back, negating the effect of the tug. So the rocket will have to be tilted outward, firing at an angle away from the asteroid. That means that pairs of rockets are needed to balance each other and keep the tug from spinning out of control.
The amazing thing about this method is that in some cases, the mass of the tug need not be all that much. For 99942 Apophis, for example, a tug massing only
a single ton
can be effective in moving the asteroid away from the keyhole even if it gets to the rock only two years in advance. To be fair, in general it will take longer to move an asteroid away from an impact trajectory; for Apophis we need only move it so it misses a small region of space, but for a direct-impact trajectory the asteroid needs to miss a whole planet. That means moving the orbit thousands of miles, which in turn means a longer lead time (or a more massive tug). One current thought, developed by Schweickart, is a hybrid solution: using a kinetic impactor (literally whacking it with another rock) or nuke to move the asteroid out of the immediate threat zone, then using the gravity tug to fine-tune the orbit so that we don’t get a surprise a few orbits later.
Still, as promising as these technologies sound, we need to be honest with ourselves. We currently don’t have the technology to implement
of these methods. We’re close—maybe only a few years from developing the gravity tug—but even lobbing a nuke at an asteroid is pretty difficult. A report written in 2007 from NASA to Congress suggests that sending an impactor to an asteroid is currently our only workable option.
But that is due to current knowledge and current technology. The B612 Foundation is hoping to incrementally test technology that will prevent an asteroid from hitting us. Even better, some of their ideas, like the gravity tug, allow us to manipulate the orbit of an asteroid any way we want. We might even be able to nudge one into a safe orbit around the Earth. It would be far too small for its gravitational pull to affect us, but close enough that we might be able to set up mining operations on it. That might sound far-fetched, but some estimates show that the metals in even a small asteroid could be worth trillions of dollars. That would make a mighty tempting target for industry.
Instead of its aiming at us, we would be well suited to aim for
There is still another lurking problem about which we need to be aware. Asteroids tend to have nice, predictable orbits. They are dead hunks of rock and/or metal, so once we observe them for a while, we can predict their orbits for decades.
In this artist’s work, Space Shuttle astronauts see a comet nucleus dozens of miles across impact the Earth. Orbiting astronauts may be the only survivors; the Earth they would eventually return to would be devastated by such an event.
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.
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,
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.
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
be impacts, and one
be big.
But the key part of that sentence is the “if we do nothing” part. The point is, we
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.
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.
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.
is what it means to be an “ordinary” star.
Let’s be clear—there
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
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+.
BOOK: Death from the Skies!
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