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Posted by baalke on October 29, 2007, 7:36 pm
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http://www.jpl.nasa.gov/news/features.cfm?feature=1510
IT Came From Vesta
Jet Propulsion Laboratory
October 29, 2007
Their infiltration began - like so many other infiltrations - with a
tell-tale contrail of smoke and flame creating a supersonic slash
across
the afternoon sky. But this time they would not go unnoticed. This
time,
two Australian station workers, just going about their job, opening a
gate to a boundary fence, witnessed their arrival. The eyewitnesses
later said they observed a "fireball with sparks coming off,"
streaking
from the south to the north, make its descent into a hummock of
spinifex
grass. It would be another 10 years before they told their story. A
decade before the world realized -- the Eucrites had arrived.
"Most people do not realize there are eucrites all are over the
planet,"
said Dr. Christopher Russell of UCLA. "How they get here is something
of
a mystery but we believe they came from Vesta."
For those of you who are not geophysicists with four decades of
service
to the cause, Vesta is the brightest asteroid in the night's sky and
the
only one visible from Earth to the naked eye. The planetoid was
discovered in 1807 by Heinrich Olbers and named after the ancient
Roman
goddess of the hearth - Vesta. But perhaps most important to this tale
is the fact that the 330-mile-wide space rock has a 285-mile-wide
gouge
out of its south pole.
"We believe it was caused by a collision of protoplanetary bodies that
caused a release of energy far beyond that of any atomic weapon known
to
man," said Russell.
It was this clash of celestial titans that gouged out an eight-mile-
deep
hole in the asteroid. On that fateful day, eons ago, one percent of
Vesta's volume was believed to be blasted into the cold blackness of
interplanetary space -- over one-half million cubic miles of its
insides
-- and outsides. It was on Vesta's outsides that the eucrites made
their
home.
But as awesome in scope as that deep space blast was, it cannot solely
explain the appearance of eucrites on Earth. After all, the orbit of
Vesta is more than twice as far from the sun as Earth's. The other
major
factor in the equation belongs to the planetary body named after the
Roman ruler of all the gods - Jupiter.
"There is a gap in the asteroid belt where objects floating around
inside it are greatly affected by Jupiter's gravity," said Russell.
"Over the centuries, this gravitational tugging can modify these
objects' trajectories about the sun. They could end up on a longer,
narrower orbit, and some of those could cross Earth's path."
So just what are these eucrites? Simply put, they are survivors. They
survived a stupendous deep space explosion. Then, they survived a
multi-billion-mile journey across the solar system, and they survived
a
3,200-degree-Fahrenheit plunge through Earth's atmosphere.
"Meteorites are hardy objects indeed," said Russell. "Eucrites are a
specific type of meteorite that the science community is confident
came
from Vesta's surface. We believe that when Vesta was forming, there
was
molten rock that flowed onto its surface that cooled rapidly. That
rapid
cooling created small crystals."
It was the unique composition of the eucrites that allows scientists
like Russell to trace the meteorites back to their parent body,
asteroid
Vesta. The meteorites' chemical identity points to Vesta because they
have the same unique spectral signature. Isotopes, oxygen atoms with
varying numbers of neutrons, in eucrites are unlike the isotopes found
for all other rocks of Earth, Moon and most other meteorites. But when
astronomers turn their spectrometers on Vesta, the signatures are the
same.
"That is why we are quite confident to say eucrites came from Vesta,"
said Russell. "Simply put, we cannot find another place in the solar
system they could be from. I believe when you discover a eucrite
meteorite, you can say with confidence -- "It Came From Vesta."
One final thing. There is a mission that will tell us more, so much
more, about eucrites and the last unexplored region of our solar
system.
NASA's Dawn spacecraft is a deep space probe that will journey into
the
heart of the asteroid belt on an eight-year odyssey to asteroid Vesta
and the dwarf planet Ceres. Dawn is on an exploration that may help
unravel these mysteries and perhaps provide some of the missing pieces
into who we are in the universe.
------------------------------------------------------------------------
Media contact: DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
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