So far, the battle between life on Earth and asteroids has been completely one-sided. But not for long. Soon, we’ll have the capability to deter asteroids from undesirable encounters with Earth. And while conventional thinking has said that the further away the better when it comes to intercepting one, we can’t assume we’ll always have enough advance warning.

A new study says we might be able to safely destroy potentially dangerous rocky interlopers, even when they get closer to Earth than we’d like.

Humanity faces a dilemma regarding asteroids. We’ve identified many of the potentially dangerous ones, but not all of them, especially smaller ones. We know there must be undetected small asteroids out there, and they can still cause a lot of damage. An asteroid’s potential damage is due not just to its size, but also its angle of impact, its velocity, and its density. (Check out Purdue University’s asteroid impact simulator.) As a general rule of thumb, an asteroid the size of a football field could wipe out a city like New York.

NASA and other space agencies are concerned when it comes to Near-Earth Objects (NEOs) and Potentially Hazardous Objects (PHOs). The US Congress gave NASA a mandate to identify and catalogue 90% of NEOs 140 meters (460 ft) in diameter or larger. Sometime in 2026, NASA plans to launch the NEO Surveyor mission to find more asteroids in our neighbourhood. But it’s doubtful we’ll ever have a complete picture of all the asteroids that could do us harm. The Universe is full of surprises.

NEO asteroid
An artist’s conception of a NEO asteroid orbiting the Sun. Credit: NASA/JPL.

The preferred method of dealing with an asteroid headed for Earth is to deflect it as one chunk using a non-explosive kinetic impactor. But we need advance warning of the asteroid’s approach to do that. If we know decades ahead of time that an asteroid is on an Earth-impacting trajectory, then we need only launch a low-mass impactor. But what if an asteroid is heading straight for Earth and we don’t have enough lead-up time? What if we have less than one year until impact?

“If we spotted a hazardous object destined to strike the Earth too late to safely divert it, our best remaining option would be to break it up so thoroughly the resulting fragments would largely miss the Earth.”

Study co-author Michael Owen, Lawrence Livermore National Laboratory.

We’ll have to blow the thing up best we can and hope that the fragments don’t strike Earth.

But blowing an asteroid up as it’s approaching Earth is a risky maneuver. The asteroid could split into a dangerous swarm of fragments. There’s also a host of technical risks. Attaching an explosive nuclear device to a rocket and launching it into space is not without risks.

A team of researchers has published a study that delves into the issue. It’s titled “Late-time small body disruptions for planetary defence” and it’s published in the journal Acta Astronautica. The lead author is Patrick King from Johns Hopkins University Applied Physics Laboratory. In the study, the term “late-time” refers to less than one year from impact.

Blowing up an asteroid might not be that difficult, in some ways. In this study, the authors wanted to focus on what happens after one is blown up. What happens to all the fragments? “Our focus is on following to a high degree of accuracy the orbits of the fragments following the disruption of a hazardous body on an Earth-impact trajectory, and if they result in any Earth impacts, estimate the scale of the consequences,” they write. This is particularly important since so many asteroids are of the “rubble-pile” type, and only loosely held together.

The study simulated a 100-meter asteroid approaching Earth and then being disrupted with a one-megaton explosive device. The explosive device wouldn’t actually strike the asteroid, it would be detonated a few meters above the surface. A detonation like that doesn’t make the asteroid disappear; it just breaks it into smaller pieces, which should pose less of a threat if all goes well.

Did you miss our previous article…