We’ve all seen a scene in a movie or television show in which Earth narrowly avoids destruction when an asteroid on a collision course is obliterated in the nick of time. But new research indicates that asteroids may well be tougher nuts to crack than we have previously believed. Bad news if there is ever an incident in which an asteroid impact must be quickly mitigated.
A new study — conducted by researchers at John Hopkins —has used our understanding of rock fracture in conjunction with a recently developed computer simulation model to recreate asteroid collisions.
The aim of the study — the findings of which are due to be published in Icarus — is to aid in the creation of asteroid impact and deflection strategies, as well as increasing understanding of solar system formation and help open the possibility of
Charles El Mir, a recent PhD graduate from the Johns Hopkins University’s Department of Mechanical Engineering and the paper’s first author, says: “We used to believe that the larger the object, the more easily it would break because bigger objects are more likely to have flaws.”
“Our findings, however, show that asteroids are stronger than we used to think and require more energy to be completely shattered.”
Though researchers have long had a good understanding of rocks and other physical materials at a lab-scale, it has been more of a challenge to extend this knowledge to huge, city-sized objects like asteroids.
In the early 2000s, a different research team created a computer model into which they input various factors such as mass, temperature, and material brittleness, and simulated an asteroid about a kilometre in diameter striking head-on into a 25-kilometre diameter target asteroid at an impact velocity of five kilometres per second.
These results suggested that the target asteroid would be completely destroyed by the impact.
In the new study, El Mir and his colleagues, K.T. Ramesh, director of the Hopkins Extreme Materials Institute and Derek Richardson, professor of astronomy at the University of Maryland, entered the same scenario into a new computer model called the Tonge-Ramesh model, which accounts for the more detailed, smaller-scale processes that occur during an asteroid collision. Previous models did not properly account for the limited speed of cracks in the asteroids.
The simulation was separated into two phases. First a short-timescale fragmentation phase and then a long-timescale gravitational reaccumulation phase.
The first phase considered the processes that begin immediately after an asteroid is hit, ones that occur within fractions of a second.
The second, long-timescale phase considers the effect of gravity on the pieces that fly off the asteroid’s surface after the impact, with gravitational reaccumulation occurring over many hours after impact.
In the first phase, after the asteroid was hit, millions of cracks formed and rippled throughout the asteroid, parts of the asteroid flowed like sand, and a crater was created. This phase of the model examined the individual cracks and predicted overall patterns of how those cracks propagate.
The new model showed that the entire asteroid is not broken by the impact, unlike what was previously thought. Instead, the impacted asteroid had a large damaged core that then exerted a strong gravitational pull on the fragments in the second phase of the simulation.
The research team found that the end result of the impact was not just a “rubble pile” — a collection of weak fragments loosely held together by gravity. Instead, the impacted asteroid retained significant strength because it had not cracked completely, indicating that more energy would be needed to destroy asteroids.
Meanwhile, the damaged fragments were now redistributed over the large core, providing guidance to those who might want to mine asteroids during future space ventures.
“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.”
Research of this nature is considered of the upmost interest by most astronomers. Dr Joseph Nuth — a researcher with NASA’s Goddard Space Flight Center who wasn’t involved with the production of this research — said in 2016 that Earth is woefully unprepared for an asteroid strike.
He adds: ” We’re particularly defenceless if it’s the size of the one that is thought to have wiped out the dinosaurs.
“They’re 50 to 60 million years apart, essentially. You could say, of course, we’re due.”
Fellow author Ramesh continues: “We are impacted fairly often by small asteroids, such as in the Chelyabinsk event a few years ago.
“It is only a matter of time before these questions go from being academic to defining our response to a major threat.”
Ramesh adds: “We need to have a good idea of what we should do when that time comes – and scientific efforts like this one are critical in helping us make those decisions.”