- Update, Dec. 24, 10:19 p.m. ET: An asteroid that has
a small chance of hitting Earth in the year 2029 was upgraded to an unprecedented
level of risk Friday, Dec. 24. Scientists still stress, however, that odds
are further observations will show the space rock won't be on a collision
course with the planet.
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- The risk rating for asteroid 2004 MN4 was raised Friday
by NASA and a separate group of researchers in Italy.
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- The asteroid's chance for hitting Earth on April 13,
2029 has now been categorized as a 4 on the Torino Scale. The level 4 rating
-- never before issued -- is reserved for "events meriting concern"
versus the vast majority of potentially threatening asteroids that merely
merit "careful monitoring."
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- The Dec. 24 update from NASA stated:
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- "2004 MN4 is now being tracked very carefully by
many astronomers around the world, and we continue to update our risk analysis
for this object. Today's impact monitoring results indicate that the impact
probability for April 13, 2029 has risen to about 1.6 percent, which for
an object of this size corresponds to a rating of 4 on the ten-point Torino
Scale. Nevertheless, the odds against impact are still high, about 60 to
1, meaning that there is a better than 98 percent chance that new data
in the coming days, weeks, and months will rule out any possibility of
impact in 2029."
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- With a half-dozen or so other asteroid discoveries dating
back to 1997, scientists had announced long odds of an impact -- generating
frightening headlines in some cases -- only to announce within hours or
days that the impact chances had been reduced to zero by further observations.
Experts have said repeatedly that they are concerned about alarming the
public before enough data is gathered to project an asteroid's path accurately.
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- Asteroid 2004 MN4 is an unusual case in that follow-up
observations have caused the risk assessment to climb -- from Torino level
2 to 4 --rather than fall.
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- Below is an edited version of the 2004 MN4 story originally
posted on SPACE.com at 9:58 a.m. ET on Dec. 24:
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- Scientists said Thursday that a recently discovered asteroid
has a chance of hitting Earth in the year 2029, but that further observations
would likely rule out the impact scenario.
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- The asteroid is named 2004 MN4. It was discovered in
June and spotted again this month. It is about a quarter mile (400 meters)
wide.
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- That's bigger than the space rock that carved meteor
crater in Arizona, and bigger than one that exploded in the air above Siberia
in 1908, flattening thousands of square miles of forest. If an asteroid
the size of 2004 MN4 hit the Earth, it would do considerable localized
or regional damage. It would not cause damage on a global scale.
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- Scientists stressed, however, that the rock would likely
miss the planet.
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- A statement was released by NASA asteroid experts Don
Yeomans, Steve Chesley and Paul Chodas.
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- "The odds of impact, presently around 1 in 300,
are unusual enough to merit special monitoring by astronomers, but should
not be of public concern," the scientists said. "These odds are
likely to change on a day-to-day basis as new data are received. In all
likelihood, the possibility of impact will eventually be eliminated as
the asteroid continues to be tracked by astronomers around the world."
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- The scientists project an asteroid's future travels based
on observations of its current orbit around the Sun. On computer models,
the future orbits are not lines but rather windows of possibility. The
orbit projections for 2004 MN4 on April 13, 2029 cover a wide swath of
space that includes the location where Earth will be. Additional observations
will allow refined orbit forecasts -- more like a line instead of a window.
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- The asteroid will be easily observable in coming months,
so scientists expect to figure out its path.
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- Most asteroids circle the Sun in a belt between Mars
and Jupiter. But some get gravitationally booted toward the inner solar
system.
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- The 323-day orbit of 2004 MN4 lies mostly within the
orbit of Earth. The asteroid approaches the Sun almost as close as the
orbit of Venus. It crosses near the Earth's orbit twice on each of its
passages about the Sun.
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- 2004 MN4 was discovered on June 19 by Roy Tucker, David
Tholen and Fabrizio Bernardi of the NASA-funded University of Hawaii Asteroid
Survey. It was rediscovered on Dec. 18 from Australia by Gordon Garradd
of the Siding Spring Survey. More than three dozen observations have been
made, with more expected to roll in from other observatories this week.
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- Earlier this week, scientists announced that a small
space rock had zoomed past Earth closer than the orbits of some satellites.
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