Where were you when Harry Stamper saved the world? I was ten years old back then, but I remember it like it was yesterday. Just moments before an asteroid the size of Texas careened into the planet, killing everyone and everything on it, that oil driller-turned-astronaut sacrificed himself; with a press of a red button, the nuclear bomb buried deep within that space rock detonated, cleaving the asteroid into two halves that drifted away from Earth. Thanks to NASA, nukes, and gnarly heroics, billions of us got to celebrate another day of living, all soundtracked to that iconic, earworm of an Aerosmith song. Armageddon may be a bombastic work of fiction. But planetary defense is real: while an increasingly advanced array of asteroid-hunting observatories diligently and constantly keeps its eyes on the heavens, space agencies are developing spaceflight technologies that can either deflect Earthbound asteroids or vaporize them entirely. And it will probably surprise you to find out that planetary defense researchers—including those at NASA’s Planetary Defense Coordination Office—have a bit of a soft spot for Armageddon and Hollywood’s wider assortment of asteroidal or cometary melodramatics.  Yes, as we all intuitively know, most of these stories of world-saving shenanigans are about as practical as a glass trampoline. But, along with the contemporaneous Deep Impact, these movies brought the very real threat of asteroid strikes to global attention. Among other factors, these movies also arguably helped convince some members of Congress to tell NASA that they were legally required to find 90 percent of all the near-Earth asteroids and comets 0.6-miles-wide or larger—those large enough to cause global devastation—within ten years. (It took 12, but they did it. None of those discovered are on Earthbound trajectories.)  If you’ve seen these movies, or perhaps the more recent (and more allegorical) Don’t Look Up, I’m sure you had the same questions I did afterward. Are nukes really the best defense against an incoming asteroid or comet? Do we really have to worry about giant space rocks or hefty snowballs wiping out civilization? Are astronauts the best way to deal with these threats? And when it comes to spotting asteroids, astronomers don’t wanna miss a thing—but how do they make sure? I reported on the story of the birth and development of the planetary defense movement in my new book, How to Kill An Asteroid—and, after having spoken to around 100 different researchers, from astronomers and emergency managers to nuclear weapon specialists and spacecraft engineers, I can confidently tell you that this is what Hollywood gets wrong—and what it surprisingly gets right—about saving the world from killer asteroids.  Greenland (2020) – small comet fragment hits Earth That space agencies predict the wrong impact location for this football stadium-size meteor – one that was detected well in advance – is, thankfully, not realistic; they would know almost exactly when and where it would hit. But the violent blast wave created by the impact is pretty realistic, and it would feel like a nuclear bomb had exploded nearby. Eep. Could an asteroid or comet kill everyone on the planet? Yes—but you shouldn’t worry about it.  This may sound a bit counterintuitive at first, considering that so-called ‘planet killer’ asteroids and comets exist. Comets, which are often rather huge and move extremely fast, have the potential to be apocalyptic. But as they spend most of their lives in the outermost fringes of the solar system, the odds of one crashing into us in this lifetime, or many lifetimes after that, is remarkably small. In contrast, millions of asteroids that have escaped the Asteroid Belt between Mars and Jupiter flit about worryingly close to Earth, and are considerably more likely to hit us. Fortunately, the larger asteroids are rarer than the smaller ones. Almost all those big enough to cause global damage in near-Earth orbits have been discovered, and none are a threat. The focus of planetary defense astronomers is ‘city killers’: asteroids 460 feet long, which, should they hit a populated area, have the potential to kill millions in a heartbeat. There are about 25,000 in near-Earth orbits, and just under half of those have been found.  Until the others are identified, nobody can say whether one is on its way to smack into the planet. The day-to-day odds of this impact happening are low, but one will find us if we wait long enough. The Expanse (2020) – stealthy asteroid hits Earth Asteroids are often depicted as moving almost gracefully slowly through the sky. Not this one: it plunges into Earth’s atmosphere, creates a super-bright fireball and hits the ocean in a matter of seconds—satisfyingly, frighteningly realistic. Would we see a dangerous asteroid coming our way before it was too late? My favorite thing about Armageddon is that NASA—thanks to a tipoff from a citizen astronomer—discovers an asteroid the size of Texas just 18 days before impact. That’s… really embarrassing, because that asteroid is hilariously elephantine. Bigger asteroids reflect more sunlight, and that one would have been gleaming in space like a giant dusty mirror.  The smaller city killers, which are of paramount concern, are harder to see. But NASA (and the European Space Agency, to a lesser extent) has an excellent array of telescopes that quest after them, with some facilities dedicated specifically to identifying near-Earth asteroids. And this decade, NASA will launch the Near-Earth Object Surveyor into space, whose infrared eye will be able to efficiently and quickly spot the telltale glow of most of the near-Earth city killer asteroids that everyone else has yet to discover. So, although we could always get unlucky, the odds of a city killer ambushing Earth are getting lower by the year. The Empire Strikes Back (1980) – dodging through an asteroid belt This scene is so iconic: the music, the spectacle, the dramatic pursuit—it’s a dream. But…yeah, sure, the asteroid field here isn’t realistic. Asteroids aren’t usually so closely bunched up, but separated by millions of miles. The TIE Fighters and the Millennium Falcon would have basically nothing to dodge or hide behind in reality, but hey, maybe things work differently in a galaxy far, far away… Would we send mavericks and astronauts to land on an asteroid and blow it up from the inside-out? Come on, you knew the answer here—at least partly—was no. When it comes to saving the world from an asteroid, a robotic spacecraft can do everything that’s needed without risking any astronauts’ lives. And you would never try to blow it up from within with a huge bomb. Not only would an asteroid fail to cleanly split into two shards, but it would make an already worrisome Earthbound projectile radioactive. If you’re going to use a nuclear bomb, you ideally want to deflect it. Blow up a nuke-armed spacecraft next to the asteroid, irradiate, and fracture that surface, turn it into a spray of debris, and it pushes the asteroid away as if it has a rocket. But, if you’re short on time, and the asteroid is small enough, you could try to use a powerful nuke to shatter it into tiny pieces—so long as you don’t accidentally send a shower of radioactive asteroid fragments into the planet.  Deep Impact (1998) – the nukes are detonated within the comet As the crew fly away from the comet, they pull the lever that detonates the nuclear warheads inside it. The spacecraft is then hit by a dramatic blast wave that knocks them about—but as there is no air in space, they wouldn’t feel anything like this. (If they’re that dangerously close to the blast, they’d be bathed in lethal radiation instead. Oops.) Are nukes really our best hope? Maybe! Nukes are certainly helpful; they deliver a big punch in one fell swoop. But— presuming you have many years to deal with the threat—in many planetary defense scenarios, using nukes to deflect an asteroid is a more troublesome option. This is partly because of the risk of a nuke-armed spacecraft blowing up in-atmosphere and scattering radioactive debris all over the place, and partly because of the messy geopolitical complications of various spacefaring nations launching objects designed for mass destruction into space. Instead, if you could, you’d deflect the asteroid with something called a kinetic impactor: a spacecraft that would ram into the space rock at just the right speed, and with just the right mass, to deflect it (not accidentally break it into smaller, but still dangerously size, pieces). This technique has, rather wonderfully, already been tested. On September 26, 2022, NASA crashed a car-size spacecraft into a (harmless) asteroid to try and deflect it. Known as the Double Asteroid Redirection Test or DART mission, it knocked that asteroid off course so emphatically that NASA passed their test with flying colors, proving that humanity could deflect an asteroid away from Earth in a genuine emergency. For All Mankind (2023) – landing on an asteroid A cosmonaut touches down on an iron-rich asteroid that space agencies intend to capture and mine—and it’s pretty realistic! City killer-size asteroids are like ball pits; if you stood on them, you’d sink into them. But this rock is far larger, so much so that it’d be more rigid and you could probably walk about on its surface without accidentally sinking into it. In Don’t Look Up, plenty of people became convinced that the incoming comet wasn’t real. That wouldn’t happen in real life, would it? It probably would. I can’t think of one national or international crisis in recent years that wasn’t swamped by conspiracy theories. And it wouldn’t help that, for most of the emergency, the threat wouldn’t be obvious to most people: if an asteroid or comet were found to be heading to Earth, and it was several years or decades out, you wouldn’t see it scorching through the night sky. It would probably feel less tangible. Every now and then, planetary defense researchers get together and set up a tabletop exercise involving an Earthbound asteroid that scientists, engineers, and policymakers at all levels of government participate in. By recreating an asteroid impact emergency and getting participants to offer suggestions as to how they’d deal with it, the hope is that weaknesses in Earth’s planetary defense system are revealed, and they can address them. The one issue that comes up time and time again, and has yet to find a solution? Misinformation—something that is closely linked with political distrust. What if the asteroid is a ruse for one country to build up its militarization of space? What if the asteroid gets deflected intentionally into a hostile nation? Why is that talking head on the news saying radioactive debris is going to be spread everywhere if the asteroid hits us? Think back to how pernicious misinformation was during the pandemic. Why wouldn’t the same nightmare unfold when the planet becomes imperiled by an asteroid? Is the United States always going to be the country that’s responsible for saving the world? It’s true that, for now, the only country to have tested a planetary defense technique (the kinetic impactor) is the U.S., and NASA’s space-based observatory, NEO Surveyor, will be the most advanced asteroid hunter by far. The Home of the Brave is currently everyone’s greatest hope. But other spacefaring nations are, to an increasing extent, stepping up to the plate. Observatories all over the world are watching the night sky for any errant space rocks, and European and Japanese space agencies have already launched their own missions to study various asteroids, for both scientific and planetary defense reasons. And, by the decade’s end, China is going to try and deflect another asteroid with its own DART-style mission. America may be best positioned to defend the planet for the time being. But as the name suggests, planetary defense is a global endeavor. Why have just one nation that’s capable of protecting all eight billion of us when you can have a dozen? The post What Hollywood gets wrong—and surprisingly right—about saving the world from killer asteroids appeared first on Popular Science.