Meteorite hit 'fast and hard'
2008-03-12 10:47
Washington - A meteorite that
struck Peru in September, digging out a deep hole and startling
nearby residents, travelled faster and hit harder than would
have been expected, researchers reported on Tuesday.
The object, which left a 15m-wide 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 24 000kph 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.
40-50 times faster
"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 Centre in Houston analysed two
chunks of dark grey 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 1 300km 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 of 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
pulverise and then they weather," said Schultz.
The findings may also help explain what caused various
craters on Mars, he said.