Original Story below..
Update, Dec. 25, 9:47 p.m. ET: The risk of an
impact by asteroid 2004 MN4 went up slightly on Saturday, Dec. 25.
It is now pegged at having a 1-in -45 chance of striking the planet
on April 13, 2029. That's up from 1-in-63 late on Dec. 24, and
1-in-300 early on Dec. 24.
Astronomers still stress that it is very likely the risk will be
reduced to zero with further observations. And even as it stands
with present knowledge, the chances are 97.8 percent the rock will
miss Earth.
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 further observations will likely show the
space rock won't be on a collision course with the planet.
The risk rating for asteroid 2004 MN4 was raised Friday by NASA and
a separate group of researchers in Italy.
The asteroid's risk rating a possible impact scenario 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."
The Dec. 24 update from NASA stated:
"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."
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.
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.
An edited version of the 2004 MN4 story originally posted on
SPACE.com at 9:58 a.m. ET on Dec. 24:
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.
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.
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.
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.
"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."
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.
The asteroid will be easily observable in coming months, so
scientists expect to figure out its path.
Most asteroids circle the Sun in a belt between Mars and Jupiter.
But some get gravitationally booted toward the inner solar
system.
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.
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.
It has been a busy stretch for asteroid scientists. Earlier this
week, researchers announced that a small space rock had zoomed past
Earth closer than the orbits of some satellites.