If an asteroid is barreling toward Earth, there's only one solution: Strike and destroy it, right? A new Johns Hopkins University study has found that, contrary to previous thought, that might not be so easy. The research plays off of a more encouraging study from the early 2000s, in which a computer model suggested that, when factoring in things like mass and temperature, if you hit an asteroid roughly 15 miles in diameter head-on with an 'impactor" that's 0.75 miles in diameter at 3 miles per second, the larger one would be destroyed upon impact. The new study, to be published in Icarus, found that wasn't the case. ("Sorry, Bruce Willis. Big asteroids die hard," quips Live Science.) Lead author Charles El Mir used the same figures as in the previous study but inputted them into a new computer model.
The model took into account an additional factor: the speed at which the cracks spread. A press release explains the technical nitty-gritty, but essentially, the simulation considered two phases: right after the strike and the hours afterward. In the strike's immediate aftermath, millions of cracks appeared and coursed through the asteroid—"parts of the asteroid flowed like sand, and a crater was created"—but the asteroid was not destroyed and still had "significant strength," indicating more energy would be needed to pulverize it. In the second phase, the asteroid's core exerted gravity on the pieces that had broken off, pulling the fragments toward the core. This changes the asteroid-coming-toward-us questions, says El Mir. "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?" (Read more asteroid stories.)