Why the Earth Gets Stronger When a Meteor Strikes

Study describes 'nonlinear force propagation' during impacts
By Arden Dier,  Newser Staff
Posted Apr 13, 2015 8:00 AM CDT
Updated Apr 18, 2015 7:00 AM CDT

(Newser) – Scientists have studied the effects of meteor strikes above ground, but what happens to soil underground during a high-speed impact? In an experiment funded by the Defense Threat Reduction Agency and recorded using a high-speed camera, physicists at Duke University set out to answer that question. They dropped a bullet-shaped metal projectile 7 feet into a pit of clear plastic beads of varying stiffness—which the projectile hit at about 15mph—to simulate an impact from a meteor or missile, according to a press release. During high-intensity impacts with hard beads, the force of the impact moved from bead to bead both deeper and faster than predicted, at speeds of up to 670mph. The beads also became stronger when pressed together during high-speed impacts, which the physicists call "nonlinear force propagation."

The experts also say the projectile faced greater resistance and didn't penetrate as deeply into the fake soil as with low-intensity impacts using less rigid beads. The scientists determined when a bead was compressed based on how it transmitted light, and "force chains" similar to lightning bolts appeared when footage was viewed through polarizing filters. But reactions from less intense impacts started at speeds of just 67mph and were contained to a smaller number of beads. The research helps explain why attempts to make ground-penetrating missiles shoot deeper into the earth with greater speed and force have proved futile. Researcher Abram Clark sums up the study like this: "Imagine you're trying to push your way through a crowded room. If you try to run and push your way through the room faster than the people can rearrange to get out of the way, you're going to end up applying a lot of pressure and ramming into a lot of angry people." (Here's how we could survive a major asteroid strike.)

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