[meteorite-list] Possibility of an Earth Impact in 2029 Ruled Out for Asteroid 2004 MN4

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Dec 27 19:41:50 2004
Message-ID: <200412280041.QAA25407_at_zagami.jpl.nasa.gov>

http://neo.jpl.nasa.gov/news/news148.html

Possibility of an Earth Impact in 2029 Ruled Out for Asteroid 2004 MN4
Don Yeomans, Steve Chesley and Paul Chodas
NASA's Near Earth Object Program Office
December 27, 2004

Over the past week, several independent efforts were made to search for
pre-discovery observations of 2004 MN4. These efforts proved successful
today when Jeff Larsen and Anne Descour of the Spacewatch Observatory
near Tucson, Arizona, were able to detect and measure very faint images
of asteroid 2004 MN4 on archival images dating to 15 March 2004. These
observations extended the observed time interval for this asteroid by
three months allowing an improvement in its orbit so that an Earth
impact on 13 April 2029 can now be ruled out.

As is often the case, the possibility of future Earth impacts for some
near-Earth objects cannot be entirely ruled out until the uncertainties
associated with their trajectories are reduced as a result of either
future position observations, or in this case, heretofore unrecognized,
pre-discovery observations. When these additional observations were used
to update the orbit of 2004 MN4, the uncertainties associated with this
object's future positions in space were reduced to such an extent that
none of the object's possible trajectories can impact the Earth (or
Moon) in 2029.

In the accompanying diagram, the most likely position of asteroid 2004
MN4 is shown at the end of the blue line near the Earth on 13 April
2029. However, since the asteroid's position in space is not perfectly
known at that time, the white dots at right angles to the blue line are
possible alternate positions of the asteroid. Neither the nominal
position of the asteroid, nor any of its possible alternative positions,
touches the Earth, indicating that an Earth impact in 2029 is ruled out.

 [graphic]
 Updated Set of Possible Positions of 2004 MN4 on April 13, 2029

The passage of the asteroid by the Earth in 2029 alters its subsequent
trajectory and expands the asteroid's position uncertainty region (i.e.,
the line of white dots increases in extent) so the asteroid's subsequent
motion is less certain than it was prior to the 2029 close Earth
approach. However, our current risk analysis for 2004 MN4
indicates that no subsequent Earth encounters in the 21st century are of
any concern.
Received on Mon 27 Dec 2004 07:41:42 PM PST