Physicists have claimed that soil and sand toughen up when struck with hefty force from meteors and missiles hitting the ground at high speed.
A lab-based test to simulate such impacts was carried out by boffins at Duke University, after they secured financial backing from the US Defense Threat Reduction Agency.
They studied what happens underground by using super slow motion cameras to track a metal projectile with a rounded tip plummeting from a seven-foot-high ceiling into a pit of beads made of clear plastic, which transmit light differently when compressed.
The simulated missile fell six metres per second, or nearly 15 miles per hour, during the test.
Researchers reckoned that the findings "may ultimately lead to better control of earth-penetrating missiles designed to destroy deeply buried targets such as enemy bunkers or stockpiles of underground weapons."
Beads in the pit were composed of varying hardness to allow the scientists to generate pulses that surged through the plastic balls at speeds ranging from 67 to 670 miles per hour, apparently.
When video recordings of each simulated impact were played back in slow motion, the physicists discovered wide variations in the network of force chains buried in the beads as a direct result of different strike speeds.
Yale University mechanical engineering post-doctoral researcher, Abram Clark, who co-authored the study – which will published this week in the Physical Review Letters journal – said:
"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." ®