Scientist answers how Peruvian meteorite made it to Earth
It made news around the world: On Sept. 15, 2007, an object hurtled through the sky and crashed into the Peruvian countryside. Scientists dispatched to the site near the village of Carancas found a gaping hole in the ground.
Peter Schultz, professor of geological sciences at Brown University and an expert in extraterrestrial impacts, went to Peru to learn more. For the first time, he will present findings from his travels at the 39th annual Lunar and Planetary Science Conference in League City, Texas, in a talk scheduled for 2 p.m. on March 11, 2008. Brown graduate student Robert 鈥淪cott鈥� Harris collaborated on the research, joined by Jose Ishitsuka, a Peruvian astrophysicist, and Gonzalo Tancredi, an astronomer from Uruguay.
What Schultz and his team found is surprising. The object that slammed into a dry riverbed in Peru was a meteorite, and it left a 49-foot-wide crater. Soil ejected from the point of impact was found nearly four football fields away. When Schultz鈥檚 team analyzed the soil where the fireball hit, he found 鈥減lanar deformation features,鈥� or fractured lines in sand grains found in the ground. Along with evidence of debris strewn over a wide area, the shattered sand grains told Schultz that the meteorite had maintained a high rate of speed as it shot through the atmosphere. Scientists think it was traveling at roughly 15,000 miles per hour at the moment of impact.
鈥淣ormally with a small object like this, the atmosphere slows it down, and it becomes the equivalent of a bowling ball dropping into the ground,鈥� Schultz said. 鈥淚t would make a hole in the ground, like a pit, but not a crater. But this meteorite kept on going at a speed about 40 to 50 times faster than it should have been going.鈥�
Scientists have determined the Carancas fireball was a stony meteorite 鈥� a fragile type long thought to be ripped into pieces as it enters the Earth鈥檚 atmosphere and then leaves little more than a whisper of its journey.
Yet the stony meteorite that struck Peru survived its passage mostly intact before impact.
鈥淭his just isn鈥檛 what we expected,鈥� Schultz said. 鈥淚t was to the point that many thought this was fake. It was completely inconsistent with our understanding how stony meteorites act.鈥�
Schultz said that typically fragments from meteorites shoot off in all directions as the object speeds to Earth. But he believes that fragments from the Carancas meteorite may have stayed within the fast-moving fireball until impact. How that happened, Schultz thinks, is due to the meteorite鈥檚 high speed. At that velocity, the fragments could not escape past the 鈥渟hock-wave鈥� barrier accompanying the meteorite and instead 鈥渞econstituted themselves into another shape,鈥� he said.
That new shape may have made the meteorite more aerodynamic 鈥� imagine a football passing through air versus a cinderblock 鈥� meaning it encountered less friction as it sped toward Earth, hitting the surface as one large chunk.
鈥淚t became very streamlined and so it penetrated the Earth鈥檚 atmosphere more efficiently,鈥� Schultz said.
Schultz鈥檚 theory could upend the conventional wisdom that all small, stony meteorites disintegrate before striking Earth. If correct, it could change the thinking about the size and type of extraterrestrial objects that have bombarded the Earth for eons and could strike our planet next.
鈥淵ou just wonder how many other lakes and ponds were created by a stony meteorite, but we just don鈥檛 know about them because when these things hit the surface they just completely pulverize and then they weather,鈥� said Schultz, director of the Northeast Planetary Data Center and the NASA/Rhode Island University Space Grant Consortium.
Schultz鈥檚 research could have implications for Mars, where craters have been discovered in recent missions. 鈥淭hey could have come from anything,鈥� he said. 鈥淚t would be interesting to study these small craters and see what produced them. Perhaps they also will defy our understanding.鈥�
Source: Brown University
