[meteorite-list] Radar Observations Refine the Future Motion of Asteroid 2004 MN4

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Feb 3 19:54:49 2005
Message-ID: <200502040054.QAA02430_at_zagami.jpl.nasa.gov>

http://neo.jpl.nasa.gov/news/news149.html

Radar Observations Refine the Future Motion of Asteroid 2004 MN4
Paul Chodas, Steve Chesley, Jon Giorgini and Don Yeomans
NASA's Near Earth Object Program Office
February 3, 2005

Radar observations taken at the Arecibo Observatory in Puerto Rico on
January 27, 29, and 30 have significantly improved our estimate for the
orbit of asteroid 2004 MN4 and changed the circumstances of the Earth
close approach in 2029. On April 13, 2029, the predicted trajectory now
passes within 5.7 Earth radii (36,350 km or 22,600 miles) of the Earth's
center - just below the altitude of geosynchronous Earth satellites.
However, an Earth collision in 2029 is still ruled out. The asteroid's
motion subsequent to the 2029 Earth close approach is very sensitive to
the circumstances of the close approach itself and a number of future
Earth close approaches will be monitored as additional observations are
received. However, our current risk analysis for 2004 MN4
indicates that no subsequent Earth encounters in
the 21st century are of concern.

In the accompanying diagrams, the most likely trajectory of asteroid
2004 MN4 is shown as a blue line that passes near the Earth on 13 April
2029. The second of the two figures is an enlarged view of the Earth
close approach circumstances. 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, effectively ruling out an Earth impact in
2029. Based on unpublished albedo contraints, the diameter of the object
is about 320 meters. At the time of the closest approach, the asteroid
will be a naked eye object (3.3 mag.) traveling rapidly (42 degrees per
hour!) through the constellation of Cancer. On average, one would expect
a similarly close Earth approach by an asteroid of this size only every
1300 years or so.

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

[graphic]
Closeup View

The passage of the asteroid by the Earth in 2029 alters its subsequent
trajectory and causes its position uncertainty region to expand rapidly
as it moves away from Earth (i.e., the line of white dots increases in
extent). As a result, the asteroid's motion is much less predictable
after the 2029 close Earth approach. Even so, the asteroid's uncertainty
region is not large enough to extend to the moon as it passes by, and so
a lunar impact is not possible.

Lance Benner (JPL), Mike Nolan (NAIC), Steve Ostro (JPL), and Jon
Giorgini (JPL) provided the Arecibo radar data that made these updated
results possible.
Received on Thu 03 Feb 2005 07:54:36 PM PST