[meteorite-list] Near-Earth Asteroid 2004 MN4 Reaches Highest Score To Date On Hazard Scale

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Dec 23 14:54:20 2004
Message-ID: <200412231954.LAA11926_at_zagami.jpl.nasa.gov>

http://neo.jpl.nasa.gov/news/news146.html

Near-Earth Asteroid 2004 MN4 Reaches Highest Score To Date On Hazard Scale
Don Yeomans, Steve Chesley and Paul Chodas
NASA's Near Earth Object Program Office
December 23, 2004

A recently rediscovered 400-meter Near-Earth Asteroid (NEA) is predicted
to pass near the Earth on 13 April 2029. The flyby distance is uncertain
and an Earth impact cannot yet be ruled out. 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. 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.

  [Diagram]
  The Orbit of 2004 MN4

  The orbit of 2004 MN4 about the Sun is shown in blue. Much of the
  asteroid's orbit lies within the Earth's orbit, which is the outermost
  white circle. The positions of the asteroid and the Earth are shown for
  December 23, 2004, when the object was about 14 million km (9 million
  miles) away from the Earth.

This object is the first to reach a level 2 (out of 10) on the Torino
Scale. According to the Torino Scale, a rating
of 2 indicates "a discovery, which may become routine with expanded
searches, of an object making a somewhat close but not highly unusual
pass near the Earth. While meriting attention by astronomers, there is
no cause for public attention or public concern as an actual collision
is very unlikely. New telescopic observations very likely will lead to
re-assignment to Level 0 [no hazard]." This asteroid should be easily
observable throughout the coming months.

The brightness of 2004 MN4 suggests that its diameter is roughly 400
meters (1300 feet) and our current, but very uncertain, best estimate of
the flyby distance in 2029 is about twice the distance of the moon, or
about 780,000 km (480,000 miles). On average, an asteroid of this size
would be expected to pass within 2 lunar distances of Earth every 5
years or so.

Most of this object's orbit lies within the Earth's orbit, and it
approaches the sun almost as close as the orbit of Venus. 2004 MN4's
orbital period about the sun is 323 days, placing it within the Aten
class of NEAs, which have an orbital period less than one year. It has a
low inclination with respect to the Earth's orbit and the asteroid
crosses near the Earth's orbit twice on each of its passages about the sun.

  [Diagram]
  Possible Positions of 2004 MN4 on April 13, 2029

  The cloud of possible positions of asteroid 2004 MN4 relative to Earth
  on April 13, 2029 is shown in white. The Moon's orbit is also shown, for
  scale. The blue arrow indicates the direction of motion of the cloud as
  it sweeps past the Earth. A tiny portion of the cloud intersects the
  Earth. A slight dip in the cloud due to the Earth's gravity is clearly
  evident. The length of the cloud is directly related to current
  uncertainties in our knowledge of this new object's orbit. As
  astronomers track this asteroid over the coming weeks and months, the
  orbit will become better determined and the cloud will shorten,
  converging on a true position which, in all likelihood, will be well
  removed from the Earth.

2004 MN4 was discovered on 19 June 2004 by Roy Tucker, David Tholen and
Fabrizio Bernardi of the NASA-funded University of Hawaii Asteroid
Survey (UHAS), from Kitt Peak, Arizona, and observed over two nights. On
18 December, the object was rediscovered from Australia by Gordon
Garradd of the Siding Spring Survey, another NASA-funded NEA survey.
Further observations from around the globe over the next several days
allowed the Minor Planet Center to confirm the connection to the June
discovery, at which point the possibility of impact in 2029 was realized
by the automatic SENTRY system of NASA's Near-Earth Object Program
Office. NEODyS, a similar automatic system at the University of Pisa and
the University of Valladolid, Spain also detected the impact possibility
and provided similar predictions.
Received on Thu 23 Dec 2004 02:54:13 PM PST