What Happens Underground When a Missle or Meteorite Slames into Earth

When a meteor slams into a planet, it causes all sorts of damage. But what occurs underground? Scientists have created new techniques to simulate high-speed missile and meteor impacts into soil and sand.

In order to simulate an impact, the researchers dropped a metal projectile with a rounded tip from a seven-foot-high ceiling into a pit of beads. During collision, the kinetic energy of the projectile was transferred to the beads and then dissipated as they butt into each other below the surface, absorbing the force of the collision.

In order to visualize the forces as they move away from the point of impact, the researchers used beads made of clear plastic that transmitted light differently when compressed. When viewed through polarizing filters, the areas of greatest stress showed up as branching chains of light called "force chains" that travel from one bead to the next during impact.

Each impact was too fast to be seen with the naked eye, so the researchers recorded it with a high-speed video camera that shot up to 40,000 frames per second. Once the scientists looked over the footage in slow motion, they found that the branching network of force chains buried in the beads varied over strike speeds.

"Imagine you're trying to push your way through a crowded room," said Abram Clark, co-author of the new study, in a news release. "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."

The findings are published in the journal Physical Review Letters.

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