Nuking an asteroid on short notice could save us

Readers of a certain age will remember a golden era of asteroid films, capped by two with very different endings. “Deep Impact” drove home the devastating consequences of letting a large piece of rock hit our planet, whereas “Armageddon,” though arguably the kitschier of the two films, was an uplifting story about technical ingenuity and sacrifice.

Now, the central premise of that movie’s storyline—essentially blasting an asteroid with a nuclear detonation—is taking center stage as our last line of defense against a potential “Deep Impact” scenario.

A new paper from researchers at the China Academy of Launch Vehicle Technology, published in Space: Science & Technology, describes two potential scenarios examining how we might actually be able to nuke a space rock—and whether it would save us.

But before we get into the technical details of nuclear explosions, let’s set the stage for the threat we face. As of July 2024, 10,933 of the 35,269 near-Earth asteroids (NEAs) discovered have diameters larger than 140 m (460 feet). If one of those rocks happened to be on a collision course with Earth (which, to be clear, none of the known ones are), it could cause continentwide or even global devastation, resulting in the deaths of millions of people.

Terrifyingly, asteroid defense experts consistently warn that simulations show there are a massive number of undiscovered NEAs that could easily blindside us. In some cases, the warning time between an NEA’s discovery and impact could be as little as a few days. That doesn’t give us a whole lot of time to mount a defense.

So it’s best if we plan it out beforehand—and modeling is one of the easiest ways to do that. With such a limited amount of time between discovery and impact, the only way we would have a chance of saving a large portion of the planet would be by imparting as much force as possible to the asteroid in an effort to either break it apart or drastically change its orbital path. And the best way we know to do that is by hitting it with a nuke.

The new paper examines two potential ways of doing this. The first is the simplest and fastest: simply fly a nuclear weapon into the side of an asteroid and detonate it with the right timing to knock it off its orbital path. This is quick, dirty and could work, but it also comes with major downsides.

In this fast scenario, selecting an ideal site for the nuclear impact is impractical, and the “coupling energy” (i.e., the energy transferred from the blast to the asteroid itself) might be relatively weak. But for it to work in the first place, the nuclear warhead will have to survive high-speed debris impacts and detonate with microsecond precision—both of which are major engineering challenges.

Anyone familiar with the details of 1990s asteroid movies knows that the main characters in “Armageddon” weren’t astronauts—they were oil prospectors. And in the movie’s lore, that meant they were really good at one thing—drilling. It’s logical that having a nuke planted inside an asteroid would make the blast more impactful (literally). But unfortunately, the likelihood of us sending a bunch of wildcatters from the fracking basins to an NEA, even with a few years’ notice, is not very high.

Instead, the paper suggests building on a recent success in an asteroid defense mission—the Double Asteroid Redirection Test (DART). This mission slammed a nonthreatening asteroid with an “impactor”—basically a giant metal rod—and intentionally shifted it from its orbit. That method itself might be enough to save Earth from a hazardous asteroid if we catch it early enough. But on short notice, it can’t produce enough energy transfer to make much of a difference. What it can produce is a crater.

In the second scenario (the flyby pre-excavation detonation mode), the mission uses a conventional penetration device—such as a “1+1” tandem impactor, in which two kinetic projectiles strike the exact same spot in sequence—to pre-excavate a deep crater reaching tens of meters across. After the crater is opened, a nuclear device follows into the pre-excavated pit to detonate.

Simulations show why that second technique is a game changer. The deeper the explosion happens inside the asteroid, the more energy is transferred into pushing the rock off its course. For an asteroid that is a kilometer (0.6 mile) in diameter, detonating a 3-megaton nuke in a shallow surface crater (i.e., one without deep pre-excavation, as in Mode 1) changed the asteroid’s velocity by only 9.2 cm/s.

But if the same nuke was detonated in a 30-meter (98-foot) crater created by the pre-excavation process, the velocity change jumped to 30 cm/s or more—in other words, more than three times as much energy was imparted if the detonation happened within a deep crater rather than on the asteroid’s surface.

Admittedly, there are some problems with the current simulations. The authors modeled the asteroids themselves as solid basalt—and any planetary defense expert will tell you that hazardous asteroids are more likely to be “rubble piles” consisting of a bunch of loosely bound rocks rather than a solid chunk of material. It’s unclear whether the simulations would hold in that much more chaotic (but likely) scenario, though someone will undoubtedly follow up with the math to show it one way or another.

Another major sticking point is how hard it is to pull off the second scenario: The launcher platform would have to match the asteroid’s orbit, conduct site reconnaissance, plan consecutive kinetic impacts and make sure the nuke is delivered to the exact same spot while navigating debris created by the impactors. Almost every step of that process is a massive engineering challenge, and each is one that we’ve only started to tackle with missions like DART.

But perhaps more important than all of these precautions is actually finding the asteroids that are potentially dangerous. NEO Surveyor, a NASA mission designed to look specifically for near-Earth asteroids, is currently scheduled to launch in September 2027. If it happens to find a rock headed straight for us, we’d better have all of our ducks in a row for how to handle it—because Bruce Willis definitely won’t be coming to save us this time.

Who’s behind this story?

Swati Mestri

Swati Mestri holds a bachelor’s degree in Electronics Engineering and has worked as a content editor since 2019. She has experience editing research documents across technology, health care, and materials science, and has a particular interest in technology and space.

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Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

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