- March 12 - NASA's Jet Propulsion Laboratory
says Earth will dodge a mile-wide bullet in the year 2028. The laboratory's
projections indicate that our planet is outside the "error ellipsoid"
that forms the bull's-eye for Asteroid 1997 XF11 - but that will need to
be confirmed by further observations and calculations.
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- AN ALERT about the asteroid's close approach created a media sensation
Wednesday when it was issued by the International Astronomical Union,s
Central Bureau for Astronomical Telegrams. Even if the asteroid passes
harmlessly past Earth in 2028 - which always has been considered the likeliest
scenario - astronomers say this closest of close calls will help society
prepare for future threats.
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- "Most likely this will fizzle, but
the next one may not," said Tom Gehrels, a leader of the Spacewatch
Project at the University of Arizona. "So this is a good exercise."
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- Asteroid 1997 XF11 was discovered just
last December by Jim Scotti, a senior research specialist for the Spacewatch
Project, which keeps track of asteroids and comets. The chunk of space
rock is thought to be about a mile wide and is currently about 150 million
miles away from Earth. It circles the sun every 1.7 years; thus, astronomers
will have ample opportunities to track its orbit over the next few years.
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- As the observations mount up, scientists
will be able to generate more precise projections of the asteroid's orbit.
The latest projections indicate that the most likely path would come within
tens of thousands of miles of Earth on Oct. 26, 2028. But the key factor
in the predictions is the error ellipsoid - a football-shaped area of probability
surrounding the asteroid's most likely course.
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- Wednesday's alert indicated that Earth
was within the error ellipsoid, meaning that based on the limited amount
of data gathered so far, there was a very small chance that the asteroid
would strike the planet. Such an impact would be the equivalent of an atomic-bomb
blast, setting off a global catastrophe. Scientists believe the impact
of a larger asteroid 65 million years ago caused the extinction of the
dinosaurs and many other species.
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- But the Jet Propulsion Laboratory said
its projections put Earth outside the error ellipsoid, meaning that there
was no chance of a collision. Thursday afternoon's forecast indicated that
the asteroid would probably not come closer than 600,000 miles. Calculations
earlier in the day showed that the greatest margin of error would still
put the asteroid 50,000 miles away from Earth.
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- The difference between a hit and a miss
is very slight in astronomical terms, and small adjustments in the asteroid's
mass or velocity would lead to different conclusions.
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- "Different calculations give slightly
different numbers on the miss distance, and that,s understandable due to
the fact that there are uncertainties in the measurements that astronomers
make," said Paul Chodas, an astronomer at the Jet Propulsion Laboratory.
"You'll get different predictions depending on whether you disbelieve
those measurements."
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- Stephen Maran, a spokesman for the American
Astronomical Society, said the different projections pointed up the need
for more observations.
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- "We certainly need better tracking
data on the asteroid," Maran said. "Independent experts of very
high reputation are getting different results."
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- Gehrens said it was clear that the chances
of an asteroid collision in 2028 were very slim at best. But he said he
"was a bit taken aback that they made such a firm statement at JPL"
that a collision was out of the question.
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- The primary purpose of Wednesday's alert,
Gehrens said, was to enlist more astronomers for the observing effort -
by turning large telescopes toward XF11 and reviewing past sky images for
traces of the asteroid that may not have been noticed before. He said any
questions about the asteroid,s path would be settled in the next few years.
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- The asteroid is currently too faint to
be seen with the naked eye, and even if it passes mere tens of thousands
of miles from Earth in 2028, it would probably look much like a star, satellite
or comet in the night sky.
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- CHICKEN LITTLE?
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- Reaction to the alert has ranged from
skepticism about a "sky-is-falling" false alarm to fatalism about
personal retirement plans. On MSNBC's Space News bulletin board, many Internet
correspondents focused on the need for closer monitoring and the formulation
of an official plan to avoid collisions with passing comets and asteroids.
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- There are several programs that monitor
near-Earth objects, including the Spacewatch Project as well as the Near-Earth
Asteroid Tracking project, operated by NASA and the Air Force. But the
plans to avert a projected asteroid strike are still largely in the sci-fi
arena - ranging from blasting objects out of the sky with lasers or nuclear
weapons to nudging them into different orbits using rocket interceptors.
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- The more dramatic methods will be illustrated
in two Hollywood movies due to be released in the next few weeks. "Deep
Impact" tells the story of an impending comet collision, while "Armageddon"
focuses on an asteroid threat.
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- On a more down-to-earth note, Rep. Dana
Rohrabacher, R-Calif., chairman of a House subcommittee on space and aeronautics,
urged President Bill Clinton to restore funding for Clementine 2, an asteroid
interceptor experiment that was axed last year in a line-item veto.
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- "This project would have been a
low-cost proof of concept for any future attempt to protect our planet
from an asteroid collision," Rohrabacher said in a written statement.
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