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- ITHACA, N.Y. - A new study
portrays the paths of asteroids in the inner solar system as a vast Los
Angeles-style traffic system crisscrossed with superhighways along which
are hurtling huge, rocky projectiles. And in the middle of the highway
network, on a possible collision path, is the planet Earth.
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- The study estimates that an armada of asteroids, 900
strong, all a kilometer in diameter or larger, present a potential hazard
to life on Earth. Some pass within a few moon distances of Earth every
year. "Sometime in the future, one of these objects could conceivably
run into the Earth," warns astronomy researcher William Bottke at
Cornell University. "One kilometer (about .6 of a mile) in size is
thought to be a magic number, because it has been estimated that these
asteroids are capable of wreaking global devastation if they hit the Earth."
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- Bottke is lead researcher on a U.S.-French team that
has discovered the spatial and size distribution of a large group of asteroids
called NEAs (for near-Earth asteroids), a vast system of orbiting rocks
in inner space, ranging in size from mere specks to more than 64 kilometers
(40 miles) in diameter. The astronomers believe the results of their observational
and computer-based study will better quantify the likelihood of future
catastrophic collisions with Earth. The survey also is expected to help
observational astronomers in improving their search for hard-to-find asteroids
that might pose a threat to the planet.
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- The team's report, "Understanding the Distribution
of Near-Earth Asteroids," appears in the latest edition (June 23)
of the journal Science. The authors, besides Cornell's Bottke, are astronomers
with the Spacewatch group at the University of Arizona's Lunar and Planetary
Laboratory and at the Observatoire de la Cte d'Azur in Nice, France.
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- Calculating which, if any, of the 900 asteroids identified
in the study could hit the Earth is tricky, says Bottke. "The problem
is that fewer than half of these Earth-threatening asteroids have been
discovered so far. Of those we have found, we can accurately predict whether
they will strike the Earth over the next hundred years or so, but we can't
project out several thousands of years. So it's possible some of these
asteroids eventually will move onto an Earth-collision trajectory. It's
a dangerous place out there."
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- The new predictions for the distribution of NEAs in the
inner solar system, say the astronomers, imply that 40 percent of the kilometer-or-larger
asteroids near Earth already have been discovered. The remaining 60 percent,
however, might be more difficult to find, says Bottke. "Most of these
asteroids are too far from Earth to be easily detected or are located in
regions of the sky that are challenging for astronomers to survey."
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- The study's authors refer to their survey as a "NEA
treasure map" indicating in which orbits most NEAs spend their time.
The researchers say the new estimate of the number of large asteroids is
about half of that predicted by similar types of analyses reported in the
past decade and is slightly larger than an estimate published recently
in the journal Nature.
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- For many decades there has been good evidence that most
of the small chunks of rocky or iron material that slam into the Earth's
atmosphere daily are chips off old blocks of asteroids. Most of the asteroids
in the solar system revolve around the sun on independent orbits, corralled
between Mars and Jupiter in a formation known as the main belt. Occasionally,
two of these asteroids -- some of them hundreds of miles in diameter --
slam into each other at great speed, causing chunks of all sizes to be
blasted off the surfaces.
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- Most of this material continues to orbit the sun in the
main belt. But sometimes the newly formed asteroids migrate to unstable
regions of the asteroid belt known as resonances, areas where the tiny
gravitational kicks produced by nearby planets such as Mars, Jupiter or
Saturn can significantly change asteroid orbits. In some cases, these changes
are enough to swing asteroids into a possible future collision path with
the Earth.
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- To find the location of these potentially threatening
and hard-to-find projectiles, the researchers used the results of the Spacewatch
group's 10-year search for asteroids in the solar system during which it
has discovered about 100 NEAs. The problem is that this tally is only a
small fraction of the predicted number of NEAs. Using a statistical technique
to compensate for the big gaps, Spacewatch astronomers were able to calculate
the total number of NEAs but not their approximate location. To obtain
the orbits of the undetected NEAs, Spacewatch astronomers combined their
NEA population estimates with theoretical models, produced by the Cornell
and Nice researchers, which show how asteroids in the main belt are transported
to the near-Earth environment.
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- Other authors of the study were Robert Jedicke of the
University of Arizona and Alessandro Morbidelli, Jean-Marc Petit and Brett
Gladman of the Observatoire de la Cte d'Azur. The study was funded by NASA
and the European Space Agency.
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- Related World Wide Web sites: The following sites provide
additional information on this news release. Some might not be part of
the Cornell University community, and Cornell has no control over their
content or availability.
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- -- University of Arizona, Lunar and Planetary Observatory,
Spacewatch Project: http://www.lpl.arizona.edu/spacewatch
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- -- Near-Earth Object Program, Jet Propulsion Laboratory:
http://neo.jpl.nasa.gov/
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- -- Asteroid and Comet Impact Hazards, NASA Ames Space
Science Division: http://impact.arc.nasa.gov/index.html
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- -- Observatoire de la Cte d'Azur: http://www.obs-nice.fr/
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- MainPage
http://www.rense.com
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