Why Smashing Asteroids to Save Earth Likely Won’t Work

Smacking an asteroid with a bomb or a smaller asteroid should shatter it into manageable pieces, right? Wrong.

You’ve probably heard by now that the movie Armageddon got everything wrong — it’s simply not possible to blow up an asteroid heading toward Earth with a few bombs. But how unfeasible is it really? A new study, published in the planetary science journal Icarus, throws any hope humanity had of nuking an incoming asteroid threat even further into the realm of impossibility. As it turns out, breaking up asteroids is extremely difficult.

The new study, led by recent Ph.D. graduate Charles El Mir of Johns Hopkins University’s Department of Mechanical Engineering, makes use of both recent progress in understanding of how rock fractures, as well as improved computer code, to model what happens when an asteroid is smacked with something large. “Our question was, how much energy does it take to actually destroy an asteroid and break it into pieces?” El Mir said in a  press release.

The answer to that question, it turns out, is “that asteroids are stronger than we used to think and require more energy to be completely shattered,” he said.

A two-step process

The simulations run by El Mir and his colleagues allowed them to study the aftermath of an asteroid collision via a “hybrid” approach that focuses on two different stages of a hit using two different types of computer code. They simulated an asteroid 15 miles (25 kilometers) across colliding with a basalt impactor 0.75 mile (1.21 km) in diameter traveling at 3 miles (5 kilometers) per second.

During the simulated collision, a material model first demonstrated the short-term fragmentation that took place within the asteroid immediately after it was struck, a process that occurs in a fraction of a second. The calculations were then passed to a different type of model called an N-body model, which demonstrated what happened over time — hours after impact — as the asteroid’s gravity influenced any small pieces that may have flown off during the collision.

Would an asteroid shatter on impact? And what would happen to those pieces as time passed? Would they fly apart, or would they recombine to re-form the asteroid, nullifying the impact’s effects?

No, the asteroid did not shatter upon impact, according to the researchers. Instead, the initial impact creates millions of internal cracks, and the areas closest to the hit actually flow like sand, allowing a crater to form. However, the cracks did not destroy the asteroid; instead, they left behind a damaged but intact body large enough to pull any smaller pieces that had flown off back onto itself, effectively reassembling the parent body.

This video shows the first phase of the simulated asteroid collision, during which a crater forms and cracks move through the interior of the target.
Johns Hopkins University
During the second phase of the collision, all the fragments that flew off are brought back down to the parent body via gravity, essentially reassembling it, albeit into a different shape and surface composition.
Johns Hopkins University

The results differ significantly from previous studies from the early 2000s, in which the code simulated an identical pair colliding. The larger body was completely destroyed in that study. But the older code, the researchers say, was not able to take into account the smaller-scale processes occurring on the asteroid during the initial collision. Because cracks propagate through an asteroid with limited speed, the authors say, they aren’t able to shatter an asteroid as easily as previously thought.

More than just movie magic

That isn’t the large-scale destruction that moviegoers are looking for, but it does tell researchers a lot about how asteroids may have evolved into the objects they are today as a result of collisions. The work could also be useful for future missions to mine material from asteroids, according to the researchers. This is because material thrown off during the collision was scattered back over the asteroid’s surface, potentially exposing internal riches for easier access.

But the picture of an asteroid hurtling toward our planet is hard to forget. While this new study indicates that a Hollywood-style explosion would not save Earth from an incoming impactor, it does hold important clues to answering the question of what we would do if Armageddon’s storyline became a reality. (And, just in case you’re getting worried, NASA’s Planetary Defense Coordination Office is already on the case, monitoring and learning more about any large objects with orbits that bring them within 0.05 AU [about 4.6 million miles, or 7 million km].)

“If there’s an asteroid coming at Earth, are we better off breaking it into small pieces, or nudging it to go a different direction? And if the latter, how much force should we hit it with to move it away without causing it to break? These are actual questions under consideration,” said El Mir.

“It is only a matter of time before these questions go from being academic to defining our response to a major threat,” added study co-author K.T. Ramesh of the Hopkins Extreme Materials Institute. “We need to have a good idea of what we should do when that time comes – and scientific efforts like this one are critical to help us make those decisions.”

READ MORE: What is the Difference Between an Asteroid, a Meteor and a Meteorite?

2 Responses

  • Thank you for the chance to comment.

    I didn’t see anything in that article about the density and composition of a typical space rock.
    Were you describing the metallic type?
    We certainly have enough samples to draw the data from.

  • What is the escape velocity of a 25km stony asteroid? It seems an impactor traveling 5km / second would scatter at least some debris at a significant fraction of the impact velocity, which i would imagine to be greater than the asteroid’s escape velocity.

    We also have the example of Vesta, which is far larger and more massive than a 25km asteroid, and presumably with a higher escape velocity. Yet fragments from an ancient collision with it continue to rain down on us many millions of miles away, so at least some of it was dislodged by the impact.

    Though possible destruction of the asteroid was the object of the study, one cannot avoid wondering how much its path was deflected in the simulations.

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