End Times: A Brief Guide to the End of the World

by Bryan Walsh

  A few things to know about modern asteroid hunting. You don’t directly look through the telescope, which is fortunate, because the room that houses it is open to the night sky, and therefore the high-altitude chill. Instead, Leonard and his apprentice Brian sat in a cramped—though blessedly heated—control room, surrounded by stacks of humming servers, walls of computer screens, and lots of coffee. The computers direct the telescope and display the images, the servers store the data from observations, and the coffee keeps the observers awake through their all-night duty rotation. Whereas the Shoemakers had to use limited and costly analog film to take glimpses of the sky—and then had to develop that film themselves and manually scan each image for moving objects—Catalina and other asteroid surveys now use what are called “charge-coupled devices,” or CCDs, thin wafers of light-sensitive silicon on top of an array of pixels. When light is concentrated on the CCD, photons fall onto the pixels and are stored there, like raindrops collected in a bucket.35 Far more images can be collected now than was ever possible during the days of analog photography, and those pictures are of higher quality and easily shareable. As a result, the pipeline of data has gone from a trickle to a torrent. And data is the lifeblood of asteroid hunting.

  But while the tools have improved, the techniques of the search haven’t changed much. After a tour of the observatory—which didn’t take long, given its compact size—I balanced on a stool and watched as Leonard directed the telescope to a single patch of sky. He paused for thirty seconds to gather enough light to make an exposure. Another benefit of CCDs is that astronomers no longer have to keep their telescope fixed for minutes to make a single image, which means far more of the sky can be covered in a single night. He shifted the telescope slightly—or slewed it, the technical term for rotating a telescope—to observe a different region of the sky, and took another exposure. The only sound inside the observatory was the grinding of gears as the telescope, originally built in the late 1960s, slid by a few degrees. Two more exposures were taken, and then Leonard returned to the first target and took another exposure, each separated in time by about fifteen minutes, until he had four exposures of the same target.

  Leonard motioned for me to come over to the computer screen. He clicked a button and the images he’d taken over the hour ran together, creating the illusion of animation, like a child’s crude flipbook. The stars, so much brighter under the telescope’s magnification than they were even through the cold and clear Arizona night, twinkled from frame to frame, the result of turbulence in the Earth’s atmosphere refracting their distant shine.

  But Leonard wasn’t looking at the stars. He was searching for something, anything, moving against the background of space, reflecting the spare light of the distant sun. (Asteroids—like planets, moons, and virtually every other object in the heavens that isn’t a star—are visible only because they reflect the light of the sun.) Catalina, like other modern sky surveys, uses software that automatically scans the exposures and highlights anything that might be an asteroid or a comet. But the program is prone to false positives, mistaking dust or bent light for a moving object. NEO hunting still requires the eyes of a trained observer, one who can parse the signal from the noise.

  Once an observing team locates a possible NEO, they relay the data to the Minor Planet Center (MPC) in Cambridge, Massachusetts, the global catalog for all things asteroid and comet. The MPC is the final arbiter on asteroid discovery, processing some 50,000 observations every day36 sent in by professional surveys like Catalina as well as amateur astronomers from around the world. Nearly all of those reports are false alarms—either outright mistakes, or NEOs that are authentic but have already been discovered by someone else, or objects that are still confined to the asteroid belt, and which therefore pose no threat to the Earth. Eric Christensen compared the process to factory trawlers that fish the sea: “We have a big net, and we’re just trying to catch whatever’s in the ocean, and most of what we catch are not NEOs.”

  Searching for asteroids is an almost monkish discipline, one that demands a fanatical attention to detail as well as the stamina to work on a mountaintop when the rest of the world is asleep. Observers spend several nights in a row at the observatory, sleeping through the days in nearby bunks, and then take several days off. “It tends to wreak havoc with your social life,” Leonard told me during a break in the observation. “The ones who make it are the ones who can keep themselves busy when they’re not on the mountain.”

  For Leonard, who has cropped graying hair and the build of a triathlete, that means exercise, in part to compensate for the eye-straining hours crouched over a computer screen on Mount Lemmon. Gene Shoemaker himself initially brought Leonard into the business. On the wall next to a bank of computer servers was a poster memorializing Shoemaker, featuring a star field above lines from Shakespeare’s Romeo and Juliet: “When he shall die, / Take him and cut him out in little stars, / And he will make the face of heaven so fine / That all the world will be in love with night / And pay no worship to the garish sun.”

  As lonely as life in the observatory could seem, it soon became clear to me that NEO hunting was a team effort. Throughout the night, Leonard and his apprentice fielded a string of requests to try to locate possible NEOs that have been spotted by other observers, somewhere else on Earth. Because asteroids won’t stay still, they need to be observed multiple times over multiple days before astronomers can know where they’re going, how large they are, and whether they might pose a threat to Earth—and they need to make those observations around the sun, which blocks much of the sky from view. Carrie Nugent compares the process to being a teacher trying to count children running around a field at different speeds, the view obstructed by a large tree.37 The faster children will appear soon enough, but the slower-moving kids may remain blocked behind the tree for some time, and the teacher—and the asteroid hunter—can only wait and watch.

  Given those challenges, it’s not surprising that mistakes do happen. On January 13, 2004, an automated telescope in New Mexico recorded an observation of a possible NEO. Staff at the MPC in Cambridge then posted the information on their website—as they always do—so that amateur astronomers could target the candidate for further observations. One spotter in Germany found it and calculated that it was on pace to grow in brightness by an astounding 4,000 percent over the next day. This was concerning, in much the same way that observing a pair of headlights getting rapidly brighter would be concerning if you were standing in the middle of the road. A NASA researcher did further work and calculated that there was a one-in-four chance that the 100-foot-wide asteroid—now named 2004 AS1—was bound to hit somewhere in the Northern Hemisphere, and that it could do so within a couple of days.

  You might think that if there were a 25 percent chance that an asteroid was about to strike, NASA would wake up the president in the middle of the night, drag them into the Situation Room, and warn them that the Earth was in imminent danger. But in 2004 there was no clear protocol for responding to the possibility of a possible hit, even from a smallish asteroid. So the astronomers kept doing what they were doing—watching the sky in the hopes of gathering additional observations that would dispel the uncertainty. The heavy cloud cover over both Europe and the United States at the time made any further observations impossible, however, until the air cleared over Colorado and an amateur astronomer named Brian Warren was able to use his telescope to search the portion of the sky where 2004 AS1 would be if it were indeed on a collision course with Earth. But the asteroid was nowhere to be found. In fact, the 2004 AS1 was more than 7.4 million miles away when it passed by the Earth, some 32 times the distance between our planet and the Moon.

  As it turned out, though, we were doubly lucky, and doubly wrong. 2004 AS1 missed the Earth, but it was closer to 1,000 feet wide, not 100, which made it about the height of the Eiffel Tower—large enough to potentially create devastation on a continental scale had it collided with the Earth.38

  Despite all the cha
llenges they face—bad weather, thin budgets, the fact that the sun stubbornly obstructs their view—asteroid hunters like Greg Leonard are very good at their jobs. They’ve located more than 8,000 NEOs in the 140-meter-plus category that NASA has been charged to track, and thousands more below that size. (Remember: there are proportionally more small asteroids out there to be found.) The Catalina Sky Survey alone discovers around three new NEOs per observation session on average.

  Toward the end of my night on Mount Lemmon—around the time I began wondering if I would be able to stay awake on the twisty drive down the mountain—Leonard and his partner zeroed in on a small asteroid, one that hadn’t been registered by the MPC yet. It was small, and later calculations showed that it posed no threat to the Earth, but the act of finding an unknown asteroid provides the kind of instant gratification that is rare in the sciences, where years or even decades can pass between the first steps to a discovery and the final recognition of publication. “We have the ability to go to the telescope and know we’ve discovered something that night,” Eric Christensen told me when I met him the next morning, once I’d come down from the mountain and had dosed myself with near-lethal amounts of caffeine.

  Those discoveries have immediate practical value. Asteroids and comets differ from other existential risks because with sufficient data, astronomers can predict the future. Take enough observations, mix in some math, and scientists can determine with remarkable precision where any NEO is likely to be in five, ten, or even a hundred years time. That’s what makes the act of asteroid hunting on lonely mountaintop observatories so necessary. It’s only through standing watch and scanning the skies, night after night, that we’re able to know what threats the cosmos may be sending our way.

  This isn’t mere science; asteroid hunting is about the preservation of the species. The jolt of excitement I felt when the Catalina team zeroed in on their new asteroid came from witnessing two human beings, in a remote observatory, playing their small roles in keeping the other seven and a half billion people on this planet safe from extinction. No other animal can do that, and neither could human beings until very recently. Asteroid hunters like Greg Leonard take that charge seriously. “I know that the chances of me dying in an asteroid impact is less than dying from a lightning strike,” Leonard told me toward the end of my time on Mount Lemmon. “But I also know that if we do nothing, sooner or later, there’s a one hundred percent chance that one will get us. So I feel privileged to be doing something.”

  Intelligence-gathering alone won’t keep the Earth safe, though. As Leonard said, given enough time, a large NEO will end up on a collision course with our planet. It’s happened before and it will happen again. So when the day comes, what will we do about it?

  The Earth’s first line of defense against incoming fire is actually the gas giant that sits fifth from the sun. Jupiter’s gravity sweeps up some of the most dangerous Earth-threatening comets and asteroids. Our second line of defense is our atmosphere. Most objects that collide with the Earth never reach the surface. Asteroids travel through the frictionless vacuum of space at speeds that reach tens of thousands of miles per hour. But when a meteor—which is what an asteroid is called once it reaches Earth—breaches the atmosphere, it hits air, which quickly piles up. Friction from air resistance causes the meteor to glow brightly and heat up to temperatures as high as 3,000 degrees.39 Up to 95 percent of the meteors that enter the Earth’s atmosphere burn up completely, and most of the rest rarely leave behind more than tiny fistfuls of rock or metal known as meteorites.40 As antimissile systems go, the atmosphere is superior to anything developed by the Pentagon.

  But even NEOs that never make it to the ground can cause substantial damage. On June 30, 1908, an asteroid or comet, perhaps 130 to 200 feet wide, exploded in the skies above the Stony Tunguska River in the heart of Siberia. The airburst produced the same amount of destructive energy as 185 Hiroshima-scale nuclear bombs. The comparison is apt—nuclear warheads are detonated in the air, rather than at ground level, to distribute the destructive force over a wider area. Tunguska was nothing less than a natural nuclear strike—albeit without the radiation—and one more powerful than any bomb humans have ever employed in wartime. The explosion annihilated more than 770 square miles of forest, pulverizing an estimated 80 million trees. It is the largest known NEO impact in recorded human history.

  Fortunately, then as now, Siberia is a place where trees vastly outnumber human beings, and no one is known to have been hurt by the strike. But Tunguska was still a close call—had the NEO arrived just four hours later, the rotation of the Earth would have brought the Russian city of St. Petersburg into the crosshairs. A 2018 White House report found that if a Tunguska-sized impactor were to hit New York, it would obliterate virtually the entire city and many nearby suburbs, taking out the world’s financial nerve center and potentially killing millions.41 “Something this size wouldn’t take down civilization, but if it hit in the wrong place, plenty of people would be dead,” said Ed Lu, a former astronaut and the executive director of the B612 Foundation, a Bay Area nonprofit dedicated to asteroid defense.

  The Tunguska strike occurred only a decade after the first NEO had even been discovered. There were no sky surveys, no astronomers searching for incoming fire, no warning, and no defense. It was only luck that the victims of the Tunguska were trees, not people. But what could we do today if astronomers discovered another largeish asteroid—say, over 300 feet—set to impact a major population center like New York or London or Tokyo?

  If the impact were predicted to occur within a few days—as briefly seemed possible in 2004—our best hope would be to move as many people as possible out of harm’s way. Were the object to hit inside the United States, the Federal Emergency Management Agency (FEMA) would be charged with preparing for the disaster and its aftermath. An incoming asteroid’s path and power can be tracked in advance, allowing astronomers to create a likely impact zone, just as meteorologists do with hurricanes. In fact, NEOs are far more predictable than weather here on Earth, let alone natural disasters like earthquakes that strike with no warning at all. And while a Tunguska-sized asteroid could obliterate a city with a direct hit, just 3 percent of the world’s land surface is covered in urban areas,42 meaning it’s much more likely that an asteroid would either strike a largely unpopulated area like Siberia or land in the oceans that cover two-thirds of the planet. That’s the good news.

  The bad news is that if an asteroid the size of the one that killed off the dinosaurs were to hit our planet today, it would have global effects no matter where it landed, and according to one study could result in fatality rates of up to 100 percent—in other words, extinction.43 In a 2013 congressional hearing, Representative Bill Posey of Florida asked then NASA administrator Charles Bolden what the strategy would be for dealing with an Earth-threatening asteroid that was discovered with three weeks’ warning. Bolden was blunt. Our strategy, he replied, would be to “pray.”44

  If we’re smart and forward-thinking, we won’t have to depend on supernatural intervention. “With enough warning—let’s say at least ten years—we could design a space mission to protect ourselves,” said Ian Carnelli, a program manager at the European Space Agency who works on asteroid surveillance and defense.

  The way to stop an NEO is to deflect it, though that word is deceptive. Rather than trying to knock an asteroid to the side, we would try to either slow down or accelerate the asteroid along its given orbital path. Remember that an impact occurs when an asteroid and the Earth intersect while traveling along their separate orbital paths. Asteroid experts compare the process to cars merging on a highway. To avoid a collision, one driver has to speed up or slow down. There’s no speeding up or slowing down the Earth, so we have to alter the velocity of the asteroid, ensuring that it arrives either too late or too early for its appointment with our planet.

  One option is to take advantage of a fundamental force of the universe: gravity. Here’s a quick high school physics r
efresher: all objects with mass or energy—planets, asteroids, even light itself—are attracted toward each other through the force of gravity. If a large object—called a gravity tractor in this case—could be placed in space near an incoming asteroid, its gravitational attraction could be just enough to slightly tug the NEO’s orbital path away from an intersection with the Earth.

  We could also take advantage of what is known as the Yarkovsky effect. Just like the Earth, asteroids rotate as they journey along their orbits, which means each half of the asteroid has a day and a night that alternate as the object spins. When the warmer daylight side of the asteroid rotates to face away from the Sun, it releases infrared photons that carry a bit of momentum from the asteroid, acting like a minuscule rocket thrust. That’s the Yarkovsky effect. As anyone who has worn a black T-shirt on a hot, sunny day knows, dark colors absorb light, while paler colors reflect it. By painting one side of the asteroid—perhaps by using paintballs made of dry powder with an electrical charge, which could theoretically survive the vacuum of space—we could use the Yarkovsky effect to tweak the asteroid’s speed. A similar method would involve employing a laser to burn away one surface of the asteroid; as it ejected the vaporized rock and metal, the asteroid would be pushed ever so slightly in the opposite direction.

  Each of these methods would create only tiny changes in the orbital path of an NEO, but if we act decades before it is predicted to hit the Earth, those tiny adjustments could accumulate over the years to ensure that the asteroid would miss our planet. But we may not have decades of warning, and if the fate of the Earth is at stake, we’d have to opt for a more direct application of Newtonian physics. An object in motion—like an asteroid—stays in motion with the same speed and the same direction unless acted upon by an unbalanced force. We could bring that unbalanced force to bear on an asteroid by ramming an unmanned spacecraft called an impactor into it. Newton’s second law—force equals mass times acceleration—would do the rest, slowing down or speeding up the NEO. If we know how large an asteroid is and how fast it is traveling, we should be able to figure out how large and how fast our impactor needs to be.