Space Chronicles: Facing the Ultimate Frontier (9 page)

The energetics of some famous impacts can be located on the table. For example, a 1908 explosion near the Tunguska River in Siberia felled thousands of square kilometers of trees and incinerated the three hundred square kilometers that encircled ground zero. The culprit is believed to have been a sixty-meter stony meteorite (about the size of a twenty-story building) that exploded in midair, thus leaving no crater. The chart indicates that collisions of this magnitude happen, on average, every couple of centuries. A much rarer sort of event created the nearly two-hundred-kilometer-wide Chicxulub crater on Mexico’s Yucatán Peninsula, which is believed to have been left by an asteroid perhaps ten kilometers wide, with an impact energy five billion times greater than the atomic bombs exploded in World War II. This is one of those collisions that take place once in a hundred million years. The crater dates from about sixty-five million years ago, and there hasn’t been one of similar magnitude since. Coincidentally, at about the same time,
Tyrannosaurus rex
and friends became extinct, enabling mammals to evolve into something more ambitious than tree shrews.

I
t’s useful to consider how strikes by comets and asteroids impact Earth’s ecosystem. In a fat book titled
Hazards Due to Comets and Asteroids
, several planetary scientists do just that regarding these unwelcome deposits of energy. Here’s a bit of what they sketched out:

• Most impactors with less than about ten megatons of energy will explode in the atmosphere, leaving no trace of a crater. The few that survive in one piece are likely to be iron based.

• A blast of 10 to 100 megatons from an iron asteroid will make a crater, whereas its stony equivalent will disintegrate, producing primarily airbursts. On land, the iron impactor will destroy an area equivalent to Washington, DC.

• A land impact of 1,000 to 10,000 megatons will produce a crater and destroy an area the size of Delaware. An oceanic impact of that magnitude will produce significant tidal waves.

• A blast of 100,000 to 1,000,000 megatons will result in global destruction of ozone. An oceanic impact will generate tidal waves on an entire hemisphere, while a land impact will raise enough dust into the stratosphere to alter Earth’s weather and freeze crops. A land impact will destroy an area the size of France.

• A blast of 10,000,000 to 100,000,000 megatons will result in prolonged climatic change and global conflagration. A land impact will destroy an area equivalent to the continental United States.

• A blast of 100,000,000 to 1,000,000,000 megatons, whether on land or sea, will lead to mass extinction on the scale of the Chicxulub impact, when three-quarters of Earth’s species were wiped out.

Earth, of course, is not the only rocky planet at risk of impacts. Mercury has a cratered face that, to a casual observer, looks just like the Moon. Radio topography of cloud-enshrouded Venus shows no shortage of craters. And Mars, with its historically active geology, reveals large, recently formed craters.

At more than three hundred times the mass of Earth, and more than ten times its diameter, Jupiter’s ability to attract impactors is unmatched among the planets of our solar system. In 1994, during the week of anniversary celebrations for the twenty-fifth anniversary of the Apollo 11 Moon landing, comet Shoemaker-Levy 9, having broken into a couple dozen chunks during a previous close encounter with Jupiter, slammed—one chunk after another, at a speed of more than 200,000 kilometers an hour—into the Jovian atmosphere. Backyard telescopes down here on Earth easily detected the gaseous scars. Because Jupiter rotates swiftly (once every ten hours), each piece of the comet plunged into a different location as the atmosphere slid by.

In case you were wondering, each piece of Shoemaker-Levy 9 hit with the equivalent energy of the Chicxulub impact. So, whatever else is true about Jupiter, it surely has no dinosaurs left.

Y
ou’ll be happy to learn that in recent years, more and more planetary scientists around the world have gone in search of vagabonds from space that might be heading our way. True, our list of potential killer impactors is incomplete, and our ability to predict the behavior of objects millions of orbits into the future is severely compromised by the onset of chaos. But we can focus on what will happen in the next few decades or centuries.

Among the population of Earth-crossing asteroids, we have a chance at cataloguing everything larger than about one kilometer wide—the size that begins to wreak global catastrophe. An early-warning and defense system to protect the human species from these impactors is a reachable goal. Unfortunately, objects much smaller than a kilometer, of which there are many, reflect much less light and are therefore much harder to detect and track. Because of their dimness, they can hit us without notice—or with notice far too short for us to do anything about them. In January 2002, for instance, a stadium-size asteroid passed by at about twice the distance from here to the Moon—and it was discovered just twelve days before its closest approach. Given another decade or so of data collecting and detector improvements, however, it may be possible to catalogue nearly all asteroids down to about 140 meters across. While the small stuff carries enough energy to incinerate entire nations, it will not put the human species at risk of extinction.

Any of these we should worry about? At least one. On Friday the 13th, April 2029, an asteroid large enough to fill the Rose Bowl as though it were an egg cup will fly so close to Earth that it will dip below the altitude of our communication satellites. We did not name this asteroid Bambi. Instead, we named it Apophis, after the Egyptian god of darkness and death. If the trajectory of Apophis at close approach passes within a narrow range of altitudes called the “keyhole,” then the influence of Earth’s gravity on its orbit will guarantee that seven years later, in 2036, on its next trip around, the asteroid will hit Earth directly, likely slamming into the Pacific Ocean between California and Hawaii. The five-story tsunami it creates will wipe out the entire west coast of North America, dunk Hawaiian cities, and devastate all the landmasses of the Pacific Rim. If Apophis misses the keyhole in 2029, we will have nothing to worry about in 2036.

Once we mark our calendars for 2029, we can either pass the time sipping cocktails at the beach and planning to hide from the impact, or we can be proactive.

The battle cry of those anxious to wage nuclear war is “Blow it out of the sky!” True, the most efficient package of destructive energy ever conceived by humans is nuclear power. A direct hit on an incoming asteroid might explode it into enough small pieces to reduce the impact danger to a harmless, though spectacular, meteor shower. Note that in empty space, where there is no air, there can be no shock waves, and so a nuclear warhead must actually make contact with the asteroid to do damage.

Another method would be to engage a radiation-intensive neutron bomb (that’s the Cold War–era bomb that kills people but leaves buildings intact). The bomb’s high-energy neutron bath would heat up one side of the asteroid, causing material to spew forth and thus induce the asteroid to recoil. That recoil would alter the asteroid’s orbit and remove it from the collision path.

A kindler, gentler method would be to nudge the asteroid out of harm’s way with slow but steady rockets that have somehow been attached to one side. Apart from the uncertainty of how to attach rockets to an unfamiliar material, if you do this early enough, then all you need is a small push using conventional chemical fuels. Or maybe you attach a solar sail, which harnesses the pressure of sunlight for its propulsion, in which case you’ll need no fuel at all.

The odds-on favorite solution, however, is the gravitational tractor. This involves parking a probe in space near the killer asteroid. As their mutual gravity draws the probe to the asteroid, an array of retro rockets fires, instead causing the asteroid to draw toward the probe and off its collision course with Earth.

The business of saving the planet requires commitment. We must first catalogue every object whose orbit intersects Earth’s. We must then perform precise computer calculations that enable us to predict a catastrophic collision hundreds or thousands of orbits into the future. Meanwhile, we must also carry out space missions to determine in great detail the structure and chemical composition of killer comets and asteroids. Military strategists understand the need to know your enemy. But now, for the first time, we would be engaged in a space mission conceived not to beat a spacefaring competitor but to protect the life of our entire species on our collective planetary home.

Whichever option we choose, we will first need that detailed inventory of orbits for all objects that pose a risk to life on Earth. The number of people in the world engaged in that search totals a few dozen. I’d feel more comfortable if there were a few more. The decision comes down to how long into the future we’re willing to protect the life of our own species on Earth. If humans one day become extinct from a catastrophic collision, it won’t be because we lacked the brainpower to protect ourselves, but because we lacked the foresight and determination. The dominant species that replaces us on postapocalyptic Earth might just wonder why we fared no better than the proverbially pea-brained dinosaurs.

• • •
CHAPTER SIX

DESTINED FOR THE STARS
^*

Video interview with Calvin Sims for
The New York Times

The Conversation

Neil deGrasse Tyson
: We need to go back to the Moon. Many people say, “We’ve been there, done that, can’t you come up with a new place to visit?” But the Moon offers important technological advantages. A trip to Mars takes about nine months. If you haven’t been out of low Earth orbit for forty years, sending people to Mars for the first time is a long way to go and a hard thing to do. A big thrust of the new space vision is to reengage the manned program in ways that haven’t been done during the past decade, and to recapture the excitement that drove so much of the space program back in the 1960s.

Calvin Sims
: So the reasons to go are to prove that we can do it again, because we haven’t done it in such a long time, and also to build consensus for it?

NDT
: We haven’t left low Earth orbit recently. We have to remind ourselves how to do that—how to do it well, how to do it efficiently. We also have to figure out how to set up base camp and sustain life in a place other than Earth or low Earth orbit. The Moon is a relatively easy place to get to and test all this out.

CS
:
NASA has estimated it could cost $100 billion, conservatively, to go to the Moon. Do you think it’s prudent to be funding this effort, especially at a point in our history when we have a war in Iraq and a lot of domestic demands?

NDT
: This $100 billion figure needs to be unpacked. It doesn’t come all at once; it’s spread over multiple years. And $100 billion, by the way, is only six years of total NASA funding.

America is a wealthy nation. Let’s ask the question, “What is going to space worth to you?” How much of your tax dollar are you willing to spend for the journey that NASA represents in our heart, in our minds, in our souls? NASA’s budget comes to one-half of one percent of your tax bill. So I don’t think that’s the first place people should be looking if they want to save money in the federal budget. It’s certainly worth a whole percent—personally, I think it’s worth more than that—but if all you’re going to give us is one percent, we can make good use of it.

Destined for the Stars

NDT
: In every culture across time, there has always been somebody wondering about our place in the universe and trying to come to terms with what Earth is. This is not a latter-day interest; it’s something deeply inherent in what it is to be human. As twenty-first-century Americans, we’re lucky to be able to act on that wonder. Most people just stood there, looked upward, and invented mythologies to explain what they were wondering about. We actually get to build spaceships and go places. That’s a privilege brought by the success of our economy and the vision of our leaders, combined with the urge to do it in the first place.

CS
: You’re saying the primary reason to venture into space is the quest for knowledge, and that humans are programmed by nature to satisfy our curiosity and to engage in the sheer thrill of discovery. Why is the allure so great that we risk human lives to get there?

NDT
: Not everyone would risk their life. But for some members of our species, discovery is fundamental to their character and identity. And those among us who feel that way then carry the nation, the world, into the future.

Robots are important also. If I don my pure-scientist hat, I would say just send robots; I’ll stay down here and get the data. But nobody’s ever given a parade for a robot. Nobody’s ever named a high school after a robot. So when I don my public-educator hat, I have to recognize the elements of exploration that excite people. It’s not only the discoveries and the beautiful photos that come down from the heavens; it’s the vicarious participation in discovery itself.

CS
: How far are we from having mass space exploration and experience by the individual person—the colonization of space? This has been a dream for a long time. Is it twenty years off? Thirty years?

NDT
: Anytime I read about the history of human behavior, I see that people are always finding some reason to fight and kill one another. This is really depressing. And so I don’t know that I trust human beings to colonize another planet, and to keep those colonies from becoming zones of violence and conflict. Also, the future has been a little oversold. Just look at what people said in the 1960s: “By 1985 there will be thousands of people living and working in space.” No. It’s now 2006, and we’ve got three people living and working in space. Delusions come about because people lose track of the forces that got us into space in the first place.

CS
: Do you have any desire yourself to venture out and explore space?

NDT
: No, never. Part of the popular definition of the word “space” is, for example, to go into Earth orbit. Well, Earth orbit can be as low as two hundred miles above Earth’s surface. That’s the distance from New York to Boston. My interest in space goes vastly beyond that—to galaxies, black holes, the Big Bang. Now, if we had ways to travel that far, sure, sign me up. Visit the Andromeda galaxy? I’m ready to leave tomorrow. But we don’t have a way to do that yet, so I’ll sit back and wait for it to come.

The Sun Revolves Around the Earth?

CS
: Americans on average know far less about science and technology than their foreign counterparts. You’ve said that unless we take steps to improve scientific literacy in America, we are headed for a crisis.

NDT
: The crisis is happening already. But I’m pleased to report that people with understanding and foresight are in our midst, some of whom have served on committees that produce documents. “A Nation at Risk,” the 1983 report by the National Commission on Excellence in Education, for example, commented that if an enemy power tried to impose on America the substandard educational system that exists today, we might have considered it an act of war. In fact, the report went so far as to say that America had essentially been “committing an act of unthinking, unilateral educational disarmament.”

CS
: Some studies have shown that only about 20 to 25 percent of the adult population can be considered scientifically literate. And one study found that one American adult in five thinks that the Sun revolves around the Earth, a notion that was abandoned in the sixteenth century. Does that surprise you?

NDT
: Didn’t you just ask me whether we’re in a crisis? Yes, we are. And yes, it concerns me deeply. There’s fundamental knowledge about the physical world that the general public is oblivious to. And by the way, science literacy is not simply how many chemical formulas you can recite, nor whether you know how your microwave oven works. Science literacy is being plugged into the forces that power the universe. There is no excuse for thinking that the Sun, which is a million times the size of Earth, orbits Earth.

CS
: This is particularly troubling because so much political debate has a basis in science: global warming, stem cell research. What do we do about this?

NDT
: I can only tell you what
I
do about it. I hate to say this, but I’ve given up on adults. They’ve formed their ways; they’re the product of whatever happened in their lives; I can’t do anything for them. But I can have some influence on people who are still in school. That’s where I, as a scientist and an educator, can do something to help teach them how to think, how to evaluate a claim, how to judge what one person says versus what another says, how to establish a level of skepticism. Skepticism is healthy. It’s not a bad thing; it’s a good thing. So I’m working on the next generation as they come up. I don’t know what to do with the rest. That 80 percent of the adults, I can’t help you there.

CS
: How do we change the way science is taught?

NDT
: Ask anybody how many teachers truly made a difference in their life, and you never come up with more than the fingers on one hand. You remember their names, you remember what they did, you remember how they moved in front of the classroom. You know why you remember them? Because they were passionate about the subject. You remember them because they lit a flame within you. They got you excited about a subject you didn’t previously care about, because they were excited about it themselves. That’s what turns people on to careers in science and engineering and mathematics. That’s what we need to promote. Put that in every classroom, and it will change the world.

China: The New Sputnik

NDT
: It’s sad but true that one of the biggest drivers fueling the space program in the 1960s was the Cold War. We don’t remember it that way; instead we remember it as, “We’re Americans, and we’re explorers.” What actually happened was that Sputnik lit a flame under our buns, and we said, “This is not good. The Soviet Union is our enemy, and we have to beat them.”

CS
: Now China is the competitor. So would you say America’s ambitious new space initiative is being driven by economic and military goals, especially since China put a man into orbit in 2003 and is close to reaching the Moon?

NDT
: There’s a proximity in time between the launch of the first Chinese taikonaut into orbit, which was October 2003, and a spate of US documents articulating a “space vision,” including the Bush administration’s Vision for Space Exploration in January 2004 and an executive order that same month establishing the Presidential Commission on Implementation of United States Space Exploration Policy, followed by NASA’s Vision for Space Exploration in February. The space vision does not state, “We’re worried about the Chinese; let’s get our people back into orbit,” but it would be imprudent not to reflect on the political climate in which these documents were issued. I have no doubt that we’re worried about our ability to compete. Let’s not forget that the vision was announced within a year of the loss of the Columbia space shuttle. It was in the wake of that loss that people started asking questions: What is NASA doing with its manned program? Why are we risking our lives to just drive around the block, boldly going where hundreds have gone before? If you’re going to put your life at risk, let it be because you’re going somewhere no one has ever been. It’s not about being risk averse: you want the risk to be matched to the goal.

CS
: How far advanced are the Chinese? Can we beat them back to the Moon?

NDT
: Of the many comparative statistics between America and other nations, one of my favorites is that there are more scientifically literate people in China than there are college graduates here in America. When I was on the president’s aerospace commission, we went around the world to study the economic climate that our own aerospace industry was now competing in. One of those trips was to China. We met with government officials and industry leaders in 2002—by the way, they all had rings from engineering schools in America—and they told us, “We’re going to put a man in space in a few years.” There was no doubt in our minds that this would happen, because we saw the channeling of their resources into this effort. We saw how they valued it for national pride. We saw how they valued it as an economic engine. What’s fresh for them is what too many Americans have taken for granted within our own nation.

CS
: Is the militarization of space or the colonization of space by different countries inevitable as a consequence of our getting there?

NDT
: We’ve got lots of space assets: communications satellites, weather satellites, GPS. There’s talk of protecting those. Is that the militarization of space that people refer to? Maybe instead they’re referring to lasers and bombs. If that were the trend, it would not be good. Militarization would contaminate the purity of the vision. The vision is to explore. There’s nothing purer in the human spirit than that.