[meteorite-list] Carancas-- still weird

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Tue, 11 Mar 2008 22:27:51 -0500
Message-ID: <s4jet39fs4nv90pacig1mjuop7bb8m6h4h_at_4ax.com>

http://www.sciencedaily.com/releases/2008/03/080311141024.htm

How The Peruvian Meteorite Made It To Earth

ScienceDaily (Mar. 12, 2008) ? 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. 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.?

These findings will be present at the 39th annual Lunar and Planetary Science
Conference in League City, Texas on March 11, 2008.




http://uk.reuters.com/article/scienceNews/idUKN1160726520080311

Streamlined meteorite hit Peru fast and hard: study
Tue Mar 11, 2008 9:59pm GMT
By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters) - A meteorite that struck Peru in September, digging out a
deep hole and startling nearby residents, traveled faster and hit harder than
would have been expected, researchers reported on Tuesday.

The object, which left a 49-foot-wide (15 meter) crater, was made of rock and,
in theory, should have disintegrated in the atmosphere long before reaching the
Earth's surface, said Peter Schultz, a professor of geological sciences at Brown
University in Rhode Island.

And it may have. But the pieces stayed together and were speeding at 15,000 mph
(24,000 kph) when they hit, Schultz told the Lunar and Planetary Science
Conference in League City, Texas.

Usually only meteorites made of metal make it to the surface intact enough to
scoop out a crater.

"They come into the atmosphere, they slow down, and they plop," Schultz said in
a telephone interview.

"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."

It landed in an arroyo, or dry stream, and the pit quickly filled with water
from underneath the surface.

Schultz said his team's observations suggest that scientists may need to change
theories about the different ways objects can hit planets. "We have to go back
to the drawing board and think again," he said.

Dozens of people who visited the crater, near Lake Titicaca and the border with
Bolivia, reported vomiting and headaches afterward. Some questioned whether the
noise and hole were actually caused by a meteorite.

"That is one of the reasons we went down. We wanted to distinguish fact from
fiction," Schultz said. "These reports of all these people being sick were
grossly exaggerated. They didn't get sick. They were surprised."

FASTBALL FROM SPACE

A team from Johnson Space Center in Houston analyzed two chunks of dark gray
rock from the meteorite and told the meeting they look nothing like meteorites
from known sources such as Mars.

Schultz, whose team inspected the crater 800 miles (1,300 km) south of Lima,
said its unusually loud and messy impact happened because it was spinning and
going so quickly.

"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."

At such high velocity, fragments may not escape past the "shock-wave" barrier
accompanying the meteorite, he said.

"It became very streamlined and so it penetrated the Earth's atmosphere more
efficiently," Schultz said. He compared it to a flock of geese drafting behind
one another in V-shaped flight.

He said this could challenge conventional wisdom that all small, stony
meteorites disintegrate before striking Earth.

"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.

The findings may also help explain what caused various craters on Mars, he said.

(Editing by Will Dunham and Eric Beech)
Received on Tue 11 Mar 2008 11:27:51 PM PDT