[meteorite-list] Brown University Scientist Answers How Peruvian Meteorite Made It to Earth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 14 Mar 2008 15:54:32 -0700 (PDT)
Message-ID: <200803142254.PAA20324_at_zagami.jpl.nasa.gov>

Office of Media Relations
Brown University

Contact: Richard Lewis
(401) 863-3766

March 11, 2008

Brown Scientist Answers How Peruvian Meteorite Made It to Earth

Brown University professor Peter Schultz's study of the Peruvian meteorite
has yielded some interesting conclusions that could upend the conventional
wisdom about the size and type of meteorites that can strike Earth.

PROVIDENCE, R.I. -- 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
"Scott" 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's team analyzed the soil where the fireball hit, he found
"planar deformation features," 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.

"Normally with a small object like this, the atmosphere slows it down, and
it becomes the equivalent of a bowling ball dropping into the ground,"
Schultz said. "It 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."

Scientists have determined the Carancas fireball was a stony meteorite -- a
fragile type long thought to be ripped into pieces as it enters the Earth's
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.

"This just isn't what we expected," Schultz said. "It was to the point that
many thought this was fake. It was completely inconsistent with our
understanding how stony meteorites act."

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's
high speed. At that velocity, the fragments could not escape past the
"shock-wave" barrier accompanying the meteorite and instead "reconstituted
themselves into another shape," he said.

That new shape may have made the meteorite more aerodynamic -- imagine a
football passing through air versus a cinderblock -- meaning it encountered
less friction as it sped toward Earth, hitting the surface as one large
chunk.

"It became very streamlined and so it penetrated the Earth's atmosphere more
efficiently," Schultz said.

Schultz's 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.

"You just wonder how many other lakes and ponds were created by a stony
meteorite, but we just don't know about them because when these things hit
the surface they just completely pulverize and then they weather," said
Schultz, director of the Northeast Planetary Data Center and the NASA/Rhode
Island University Space Grant Consortium.

Schultz's research could have implications for Mars, where craters have been
discovered in recent missions. "They could have come from anything," he
said. "It would be interesting to study these small craters and see what
produced them. Perhaps they also will defy our understanding."

IMAGE CAPTION:
[http://www.brown.edu/news/2007-08/07-113.jpg (40KB)]
The Carancas Fireball
Planetary geologists had thought that stony meteorites would be destroyed
when they passed through Earth's atmosphere. This one struck ground near
Carancas, Peru, at about 15,000 miles per hour. Brown University geologists
have advanced a new theory that would upend current thinking about stony
meteorites.

Image: Peter Schultz, Brown University
Received on Fri 14 Mar 2008 06:54:32 PM PDT