Nuking An Asteroid on Short Notice Could Save Us - Universe Today

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Artist's concept of the DART satellite. Credit - NASA / JHU APL

Readers of a certain age will remember a golden area of asteroid films, capstoned by two with very different endings. Deep Impact engrained the devastating consequences of letting a large piece of rock hit our planet, whereas Armageddon, though arguably the more kitschy of the two films, was an uplifting story about technical ingenuity and sacrifice. And now, the central crux 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, and 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 actually 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, out of 35,269 total Near-Earth Asteroids (NEAs) discovered, we know of 10,933 NEAs with a diameter larger than 140 m. 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 continent-wide 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.

Fraser offers a lesson how critical it is that we find all the potentially deadly asteroids, before they find us.

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 through 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 of 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 also the 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 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 even work in the first place, the nuclear warhead will have to survive high speed debris impact and detonate with microsecond precision - both of which are major engineering challenges.

Anyone familiar with the details of their 90s asteroid movies, the main characters of 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.

Once we find them, we need to stop them, and Fraser discusses different techniques to do so.

Instead, the paper suggests building off of a recent success in an asteroid defense mission - the Double Asteroid Redirection Test (DART). This mission slammed a non-threatening asteroid with an “impactor” - basically a giant metal rod - and intentionally shifted it from its orbit. That method in 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 of an energy transfer to make much of a difference. But 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 where two kinetic projectiles strike the exact same spot in sequence—to pre-excavate a deep crater reaching up to tens of meters across. After the crater is opened, a nuclear device follows into the pre-excavated pit to initiate detonation.

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 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...