Big Crater Carved By Mysterious Meteorite

In September 2007 a fireball flew in from space and hurtledthough Earth's atmosphere, smashing into the ground in Peru while awestruckwitnesses watched. It was the first time people have witnessed space debrisforming an impact crater live.

But the witnesses'reports and the geological aftermath stunned scientists. This meteoriteseemed to have flown in much faster than scientists thought possible for anobject of this kind, and it apparently survived entering Earth's atmosphereintact, rather than splintering into bits as experts thought it should have.

"Many people thought this was afake," said Peter Schultz, a Brown University planetary geologist whotraveled to Peruto analyze the crater. "It just didn’t make sense with what we understandof collisions with this type of fragile rock. Coming through the atmosphere theyget stressed so highly that they typically break apart. But this one didn’t dothat."

Let's go look

A few months after the impact, Schultz went to investigatethe crater along with Peruvian scientists and government officials. Hepresented his findings today at the 39th annual Lunar and Planetary ScienceConference in League City, Texas.

Schultz found fractured lines in sand grains and compressedmixtures of earth and meteorite around the 49-foot-wide craternear the village of Carancas. These, along with widespread debris from themeteorite's crash landing, told him it landed at high speed, likely around15,000 miles per hour at the moment of impact.

The meteorite was a common type, a chunk of silicate rockcalled a stony meteorite. Usually a projectile such as this would be sloweddown by the drag of Earth's atmosphere. By the time it landed, it would betraveling at the normal terminal speed of any object falling from the sky, andwould probably dint a hole in the ground, but not a crater.

"Essentially Carancas threw us this high-speed curveball,"Schultz told SPACE.com. "The mysteryis why it didn’t slow down and how did it make it all the way to the Earth intactto form a crater? These are questions we have to resolve."

New thinking

Scientists have several hypotheses about what might havehappened. Perhaps as the meteorite hurtled through the atmosphere it melted andmorphed, becoming more of an aerodynamic needle-shape that could resist stressand survive in one piece. Plus, this shape would help it hold on to its speed,since the surface area exposed to atmospheric drag forces would be reduced.

"But the mystery is, why wouldn’t all objects reshape?"Schultz said. "Maybe it requires special circumstances, like the angle ofentry."

The unique event could change scientists' thinking about howmeteorites act, and how other craters on Earth were formed, especially onessimilar to the Carancas site, where water has since collected in the hole.

"What does this mean for other small water-filledponds?" Schultz asked. "You just wonder how many of these havepowdered remains of a stony meteorite at the bottom, something that would bedifficult to find after time."

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