Asteroids are much harder to blow up in order to save Earth than we had thought, scientists warn

'It is only a matter of time before these questions go from being academic to defining our response to a major threat'

It will be much harder than we have realised to blow up an asteroid and save the planet, scientists have warned.

Experts have repeatedly warned that it is a question of when not if the Earth will be hit by the arrival of a potentially disastrous asteroid. But films have suggested a simple if high-tech response: launching heroes into space to blow it up before it ever gets here.

In real life, however, those asteroids could be far more difficult to destroy than we knew. That is according to a new study from scientists at Johns Hopkins, who simulated the ways that an asteroid collision might happen and how such a space rock would fracture.

Researchers hope the discoveries could better prepare humanity for such a catastrophic event by improving the ways we can deflect or destroy asteroids that threaten us. They could also help us understand how solar systems form and the ways we might be able to mine asteroids for the precious materials that are thought to be inside.

Any big asteroid that was hurtling towards Earth could prove deadly to a vast proportion of the Earth's population. Scientists had hoped that their size could be used against them – anything that big could theoretically break apart more easily – but that might not be such a comfort, the new study shows.

"We used to believe that the larger the object, the more easily it would break, because bigger objects are more likely to have flaws," said Charles El Mir, a recent Ph.D graduate from the Johns Hopkins University's Department of Mechanical Engineering and the paper's first author, in a statement.

"Our findings, however, show that asteroids are stronger than we used to think and require more energy to be completely shattered."

Researchers have a full understanding of rocks at the scale they can be understood in a laboratory, or roughly the size of a person's fist. But it is difficult to know how that understanding will apply if the rock is the size of a city, like an asteroid.

Previous attempts tried to simulate those objects, by creating a computer model that accounted for things like temperature and brittleness and seeing how a large asteroid might react when struck by a smaller one. It seemed to show the target asteroid would be completely destroyed.

But the new study looked at the same scenario with new computer models. The new work includes more detailed and smaller-scale processes – allowing them to better account for the way cracks would form across the asteroid.

"Our question was, how much energy does it take to actually destroy an asteroid and break it into pieces?" said El Mir.

They found that after the initial impact, millions of cracks formed and rippled throughout the asteroid. That allowed parts of it to flow like sand, and left a crater in its surface.

But when they accounted for the gravity would act on those broken up pieces, they found that the huge damaged core would still pull the fragments around it. It meant the targetted asteroid kept its strength because it had not completely cracked, and the damaged fragments were strewn across the core in the middle.

That could prove useful to asteroid miners who would be able to pick through those pieces and find the useful materials. But it means that anyone looking to destroy a dangerous asteroid would need to use more energy to get rid of it.

"It may sound like science fiction but a great deal of research considers asteroid collisions. For example, 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," says El Mir.

"We are impacted fairly often by small asteroids, such as in the Chelyabinsk event a few years ago," K.T. Ramesh, director of the Hopkins Extreme Materials Institute​. "It is only a matter of time before these questions go from being academic to defining our response to a major threat. 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."