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

by Bryan Walsh

  NASA knows this method can work, because they’ve tried it—though not exactly on purpose. In 2005, the Deep Impact spacecraft rendezvoused with the comet Tempel 1, some 266 million miles from Earth. Upon arrival, Deep Impact—which, for the record, was not named after the film—released an 820-pound impactor that rammed into the comet at about 23,000 mph, delivering a jolt of force equivalent to 4.8 tons of TNT.45 Given that the comet was nearly four miles across while the impactor was the size of a washing machine, there was no measurable deflection to speak of—that’s Newtonian physics for you—but the collision did leave a measurable crater, and gave NASA at least an outline of how a kinetic impactor could work on a smaller asteroid, or with a bigger impactor. Which brings us to nukes.

  The more force we can deliver to an NEO, the more we can alter its orbit—and for better or for worse, there is nothing in the human arsenal more forceful than a nuclear weapon. If we needed to deflect a large asteroid, or one that was already close to Earth—so the change in the NEO’s orbit would need to be more extreme—nukes would likely be our only alternative. Erika Nesvold, an astrophysicist formerly with the Carnegie Institution for Science, devised an algorithm called Deflector Selector that simulated 18 million attempts to prevent an asteroid impact. She concluded that a nuclear option was the right call for as many as half of the simulations. “It’s not all that surprising,” she told me. “This is a physics problem, and nukes have the most energy.”

  What we wouldn’t do is simply fire a bunch of intercontinental ballistic missiles at the asteroid and hope to blow it to smithereens, as if we were playing a real-life game of Missile Command. It may sound counterintuitive, but you don’t want to blow up an asteroid if you’re trying to defend the Earth. There’s no telling where the resulting debris might hit, and as Shoemaker-Levy 9 demonstrated, a broken impactor can still pack a serious punch. One 2019 computer model study found that if an impactor did break up an asteroid on a collision course, the space rock would eventually pull itself back together.46 As with other deflection techniques, the aim is to speed up or slow down the asteroid along its orbital path. Nuclear weapons just provide extra oomph.

  One method would be to explode a nuclear device several hundred feet away from the asteroid. Space is a vacuum, so there is no air to carry the destructive force of a shockwave as on Earth, but the high-energy gamma rays, X-rays, and neutrons released by the detonation would hit the nearby surface of the asteroid and vaporize part of it, creating plasma that ejects particles back into space and so thrusts the asteroid in the opposite direction. Hopefully nothing gets blown up—especially the Earth. “This isn’t about sending Bruce Willis to the asteroid with a bomb,” said Carnelli.

  About that. You can’t discuss asteroid defense—even among PhD-holding astrophysicists—without Bruce Willis and Armageddon coming up sooner or later. On the one hand Armageddon—and the somewhat more scientifically sound Deep Impact—introduced audiences to the existential threats posed by NEOs in visceral fashion, and proved that we weren’t helpless to stop them. On the other hand, certain licenses were taken with the science. In Armageddon the killer asteroid is described as being “the size of Texas,” reportedly because Michael Bay didn’t think that audiences would believe than an NEO six or seven miles across would possibly be big enough to wipe out the human race. (It would be.) A group of scientists at the University of Leicester in Britain calculated that the bomb Willis and his crew planted after drilling into the asteroid would have needed at least 50 billion megatons of kinetic energy in order to blow apart a Texas-sized NEO. For the sake of comparison that’s a billion times more powerful than the biggest nuclear bomb ever built, the Soviet Union’s Tsar Bomba.47

  NASA also wouldn’t send astronauts—let alone a team of untrained oil rig drillers—to intercept an incoming asteroid. Any mission would be unmanned. But it is possible, as a last-ditch effort should a large NEO be discovered with little time to spare, that NASA might take a page from the Michael Bay playbook and try to plant a nuclear bomb inside an asteroid. The agency has studied using a Hypervelocity Asteroid Intercept Vehicle, a theoretical spacecraft that would crash into an oncoming asteroid at high speeds, burrowing several feet deep into the object, before setting off a nuclear device.48 Detonating a nuclear warhead below the surface of an asteroid, rather than on it, could increase the explosive power by as much as twentyfold. It’s worth noting that one of the reasons the U.S. National Nuclear Safety Administration gave for not dismantling America’s largest atomic warheads after the Cold War was the possibility that they might be required for planetary defense.49

  So we have theories for how we might protect our planet in the event of an NEO strike. But what we don’t have—yet—is an organized and practiced strategy for that defense. Creating and executing that plan is largely the job of one man: Lindley Johnson, NASA’s first planetary defense officer.

  In 1994, around the time that the Shoemakers and David Levy were searching for NEOs at the Palomar Observatory, Lindley Johnson was a major in the U.S. Air Force, studying advanced space operations at the Air Command and Staff College in Montgomery, Alabama. Johnson was well versed in threats from above. He had already served at the North American Aerospace Defense Command (NORAD), the U.S.-Canadian military unit that provides surveillance against incoming ballistic missiles, as well as the Space and Missile Systems Center in Los Angeles. Unusually for the time, and especially for a military officer, Johnson was already convinced of the danger from NEOs. Shortly after the Shoemaker-Levy 9 comet was discovered in March 1994—but, crucially, before astronomers watched it collide with Jupiter, inspiring the first sustained efforts at planetary defense—Johnson published a paper describing early theories about how to deflect an NEO on a collision course with the Earth. It was met with a shrug—few people at the time, especially in the government, believed that an object from space could threaten our planet.

  The Shoemaker-Levy 9 collision in July 1994 changed the course of Johnson’s career. He was assigned to the Air Force’s Space Command, where he pushed for collaboration with NASA, including on projects that employed space surveillance telescopes to search for asteroids and comets. After retiring from the military in 2003, Johnson went to work for NASA. For years he was the space agency’s only senior manager working on NEOs, but he helped push for a steady increase in the asteroid-hunting budget. In 2015 NASA created the Planetary Defense Coordination Office and put Johnson in charge of, effectively, defending the Earth.

  Planetary Defense Officer is a very grand title for someone whose work by his own admission mostly consists of interdepartmental coordination. After arriving at NASA headquarters in Washington each morning, Johnson checks what he calls “the night’s catch”—the collection of NEOs that have been discovered overnight by observatories like the Catalina Sky Survey and cataloged by the Minor Planets Center. He asks questions: Do any of these NEOs fall into the category of potentially hazardous, meaning they could pass within 5 million miles of the Earth? Have astronomers calculated any new asteroid approaches that could threaten the planet? Imagine it as the President’s Daily Briefing, only the threats are space rocks, not terrorists and hostile governments.

  If something does pose a potential impact risk to the Earth, it would be Johnson’s responsibility to push the alert up through NASA, to the White House Office of Science and Technology and eventually to the president. That’s only happened once so far during Johnson’s time with NASA, in 2008, when astronomers correctly predicted that a small asteroid would reach the Earth and largely burn up before impact.50 It marked the first time scientists had managed to successfully forecast an impact event in advance of impact. Johnson made the prediction public, mostly so the sight of a sudden flash in the sky wouldn’t be misinterpreted as something military. “We didn’t want to get anyone too excited about a big explosion in the atmosphere,” he told me.

  More recently, Johnson and his colleagues took advantage of a near-miss by a house-sized asteroid on October 12,
2017, to test out the Earth’s nascent NEO warning system. The asteroid never posed a direct threat, but it did come within 28,000 miles of the planet—as close to the Earth as man-made satellites—which made it perfect as a dry run. “We picked it up, tracked it, got a high-precision prediction of the close approach, and then we used that to exercise our notification system to the U.S. government and our international partners,” Johnson said.

  Johnson and his team have found that while asteroids and comets may be more predictable than other natural threats, they still have an element of ambiguity. Even if scientists suspect that a newly discovered NEO could be on a future impact course with Earth, they won’t be certain—at least not at first, especially if a potential collision is years or even decades away. As asteroids whiz close to the Earth, their orbit will be tweaked by the planet’s strong gravitational field. Should an asteroid travel through a precise range of altitudes called a “keyhole” during a first pass by Earth, its path can be changed in such a way that it will be all but guaranteed to impact the planet during its next orbital go-round. (Remember that asteroids, like the Earth, orbit the sun, so one that passes by will come around again.)

  Scientists, though, can only estimate the chances an asteroid will hit that precise keyhole—hence the slight uncertainty around a future impact. Shortly before Christmas 2004, a 1,200-foot-wide asteroid known as 99942 Apophis—named after the Egyptian snake god symbolizing chaos—was initially calculated to have a 2.7 percent probability of hitting the Earth on April 13, 2029.51 That probability might seem minuscule, but ask yourself this: would you get on a plane if there were a 2.7 percent chance it would explode in midair? Fortunately scores of additional observations helped clarify Apophis’s position, and astronomers concluded that there was zero chance of it hitting the Earth on its 2029 or 2036 go-round. In fact, the chance of Apophis hitting the Earth anytime over the next century is a microscopic 0.00089 percent52 as of early 2019—though that is higher than your chance of dying in a plane crash.53

  Should it strike the Earth, an asteroid the size of Apophis would hit with the power of more than a billion tons of TNT54 and lay waste to an entire state, if not much more. But it would still take years of additional observation before astronomers could be more certain whether or not an impact was going to occur. Even once an impact is determined to be likely, astronomers would produce not a bull’s-eye on the planet, but rather a “risk corridor”—a narrow band stretching across the Earth that marks the territory where an NEO is predicted to land. There’s an inevitable trade-off in asteroid deflection—the more time astronomers are given to observe an asteroid, the more precise impact probability and any risk corridor will be, but that leaves less time for a deflection effort, which would almost certainly take a decade or longer to plan and complete.

  And who, ultimately, would make the decision about whether to give the green light to such a mission, one that would cost billions of dollars and might not even work? Large NEOs may be the definition of a global threat, but NASA’s budget is greater than that of all other space-faring countries combined,55 and only the United States has the experience and the technology to lead a deflection mission. In the event of an incoming asteroid, the president would likely put together a Planetary Impact Emergency Response Team, which would include NASA, the Department of Defense, the Department of Energy (which oversees the U.S. nuclear arsenal), and FEMA, among others. Internationally, there are other space-capable nations like Russia or China that could convene under the auspices of the United Nations Committee on the Peaceful Uses of Outer Space, the closest thing the world has to a legal body for space law.56

  One might assume that if a major asteroid were discovered well on its way toward our planet, we’d come together as a species and do whatever it takes to defend ourselves, up to and including mobilizing our most powerful nuclear weapons. But the 1967 Outer Space Treaty explicitly bans the use of atomic weapons in space, presenting a legal obstacle. And consider this—in the early 1990s, the astronomer Carl Sagan identified what he called the “deflection dilemma.” Any technology that would be powerful enough to alter the course of an asteroid away from the planet could theoretically be used to direct an asteroid toward a target.57 Like an enemy country, for example.

  That might seem paranoid. What leader would play geopolitical games at a moment of existential peril? But in a world where international trust is evaporating and science itself is no longer believed, how much trust would the rest of the world have in the word of the U.S. president—especially the current one—that an asteroid deflection mission using untested technology would truly be peaceful, or successful? Even a deflection mission launched with the best of intentions could inadvertently nudge an incoming asteroid away from one country and toward another. Like physicians, planetary defenders should first do no harm, but the pressure to do something, anything, in the event of an incoming asteroid would surely be intense.

  The quickest way to instill global confidence in our ability to deflect an asteroid when the pressure is on would be to deflect an asteroid when the pressure is off. Practice makes perfect. That’s why NASA and its partners at the European Space Agency (ESA) have plans to launch the Double Asteroid Redirection Test (DART) spacecraft in 2022. Its target will be the binary asteroid Didymos, which came within 4.5 million miles of the Earth during an orbital pass in 2003. Didymos means “twin” in Greek—one larger asteroid, Didymos A, is orbited by a smaller rock called Didymos B.58 The DART probe, which is about the size of a refrigerator, will impact Didymos B in an attempt to alter its trajectory. The mission will mark the first time that earthlings have purposefully tried to modify the orbit of a heavenly body, and it could serve as proof of concept for a future deflection mission.

  NASA deserves some credit for the steps it has taken on planetary defense in recent years, including the creation of Johnson’s job. Before the Planetary Defense Coordination Office was established in 2015, responsibility for asteroid hunting and defense was scattered around a number of departments—a lack of focus NASA’s own inspector-general criticized the agency for in a damning 2014 report.59 In September 2018, the White House announced a plan to nearly triple spending on planetary defense to $150 million in 2019, with much of the money earmarked for the DART mission. That additional funding needs to be approved by Congress,60 although Americans seem to support it—a 2018 Pew poll found that protecting the planet should be the number two priority of the U.S. space program, after researching climate change, another existential threat.61

  “In the order of things that people should be worried about, [NEOs] isn’t highest on the list,” Johnson told me. “But it does have the potential to be the most devastating natural disaster known to man. All the money that we will have spent on it would have been worthwhile if it prevents an event that could take hundreds of billions of dollars to recover from—if we are even able to recover. It’s definitely worth governments spending a bit of their treasure to find these things ahead of time, because you can’t do anything unless you find them.”

  But what if we can’t find them?

  On February 15, 2013, Lindley Johnson was in Vienna, preparing to share an asteroid defense plan with the United Nations Committee on the Peaceful Uses of Outer Space. The timing was perfect. That day an asteroid designated DA14 came within just 17,000 miles of the Earth. NASA and its partner observatories had been tracking the asteroid for a year, and knew with 100 percent certainty that it would pass near but not threaten the Earth. It was set to be the ideal demonstration of how smart NEO surveillance can keep a dangerous asteroid from taking us by surprise.

  Except that isn’t how we’ll remember February 15, 2013. At 9:20 a.m. local time that same day, a different asteroid, some 65 feet across, penetrated the Earth’s atmosphere over Russia. Speeding at more than 40,000 mph, the now meteor exploded in an airburst some fourteen miles above Chelyabinsk Oblast, a rugged, industrial region in the Ural Mountains known for its military and nuclear industries.

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p; The light from the explosion—captured in dash cams and home videos—burst yellow, and then orange, and briefly glowed brighter than the sun, with a force estimated at 400 to 500 kilotons of TNT.62 Some 1,500 people were injured in the blast, mostly from glass shattered by the shock wave, and more than 7,200 buildings across the region were damaged. People were blown off their feet, and in the aftermath the air smelled of gunpowder and sulfur; monitoring stations as far away as Antarctica could detect the detonation. “I opened the window from surprise—there was such heat coming in, as if it were summer in the yard,” wrote one witness. “In several seconds there was an explosion of such force that the window flew in along with its frame, the monitor fell and everything that was on the desk.”63 Later analyses showed that the Chelyabinsk meteor was the largest natural object to enter the Earth’s atmosphere since the Tunguska event, more than a century earlier. And scientists didn’t have a clue the asteroid was coming until it was too late.

  This is the dirty secret of asteroid hunting—while we’ve managed to locate more than 95 percent of the NEOs that are larger than 1 kilometer, it’s proven much more difficult to find the far more numerous asteroids below that size. Recall that in 2005 Congress charged NASA with locating 90 percent of the NEOs larger than 140 meters by 2020. As of 2018, NASA and its partners had found about one-third of the estimated 24,000 or so NEOs in the target class. As for meeting the deadline, Johnson told me, “That ain’t going to happen.”