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Among the asteroids with a near-Earth
orbit is 2004 MN4. According to the latest projection
from Paul Chodas, Steve Chesley, Jon Giorgini and Don
Yeomans of NASA's
Near Earth Object Program Office, on 13 April 2029,
2004 MN4 is projected to pass within 36,350 km (22,600
miles) of the Earth's center. This is closer to the
surface than geosynchronous weather satellites!
NEODyS
(Near Earth Objects-Dynamic Site) of the University
of Pisa in Italy has assigned asteroid 2004 MN4 its
own home
page on the web, which states, "This object
has the possibility of impacting the Earth, with a small
but non-zero probability."
NASA's
Near Earth Object Program has considerable information
about this space rock, which is believed to have a diameter
of about 320 meters (1,050 feet). The most interesting
feature is a Java
applet animation that shows the relative position
of the Sun, planets and 2004 MN4 over a period of decades.
You can select increments of 1 hour; 1, 5 or 10 days;
1, 3 or 6 months; or 1 year. You can then display the
orbital positions as a movie. You can tilt the plane
of the orbits, zoom in for a closer look, and change
the center of the screen to the Sun, a planet or the
asteroid.
Figure 1 is an image from the applet
for 13 April 2029. Figure 2 shows the projected trajectory
of 2004 MN4 with respect to the Earth and the Moon on
13 April 2029. This image is based on recent radar observations
of 2004 MN4 from the Arecibo Observatory in Puerto Rico.
The white bar denotes the uncertainty in the position
of the asteroid at its closest point to Earth. Figure
3 is an enlarged view that dramatically illustrates
the proximity of the asteroid to Earth.
According to the NASA's
Near Earth Object web site, "At the time of
the closest approach, the asteroid will be a naked eye
object (3.3 magnitude) 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."
While the NEO (Near Earth Object) community
are agreed that the probability of 2004 MN4 striking
Earth is very low, what might happen if it did?
For a first approximation, we can turn
to the Earth
Impact Effects Program developed by Robert Marcus,
H. Jay Melosh, and Gareth Collins. For the scenario
that follows, I entered estimated parameters for 2004
MN4 and assumed the asteroid would strike a continent
or large island at a region overlain by sedimentary
rock. Here are the calculated effects on an observer
1,000 km (621 miles) away from ground zero:
Impact Effects
Robert Marcus, H. Jay Melosh, and Gareth Collins
Please note: the results below are
estimates based on current (limited) understanding of
the impact process and come with large uncertainties;
they should be used with caution, particularly in the
case of peculiar input parameters. All values are given
to three significant figures but this does not reflect
the precision of the estimate. For more information
about the uncertainty associated with our calculations
and a full discussion of this program, please refer
to this article
Your Inputs:
Distance from Impact: 1000.00 km = 621.00 miles
Projectile Diameter: 320.00 m = 1049.60 ft = 0.20 miles
Projectile Density: 3000 kg/m3
Impact Velocity: 12.60 km/s = 7.82 miles/s
Impact Angle: 45 degrees
Target Density: 2500 kg/m3
Target Type: Sedimentary Rock
Energy:
Energy before atmospheric entry: 4.09 x 1018 Joules
= 9.76 x 102 MegaTons TNT
The average interval between impacts of this size somewhere
on Earth during the last 4 billion years is 2.2 x 104years
Atmospheric Entry:
The projectile begins to breakup at an altitude of 49300
meters = 162000 ft
The projectile reaches the ground in a broken condition.
The mass of projectile strikes the surface at velocity
12.1 km/s = 7.49 miles/s
The impact energy is 3.74 x 1018 Joules = 8.94 x 102MegaTons.
The broken projectile fragments strike the ground in
an ellipse of dimension 0.909 km by 0.643 km
Major Global Changes:
The Earth is not strongly disturbed by the impact and
loses negligible mass.
The impact does not make a noticeable change in the
Earth's rotation period or the tilt of its axis.
The impact does not shift the Earth's orbit noticeably.
Crater Dimensions:
Crater shape is normal in spite of atmospheric crushing;
fragments are not significantly dispersed.
Transient Crater Diameter: 3.74 km
= 2.32 miles
Transient Crater Depth: 1.32 km = 0.821 miles
Final Crater Diameter: 4.47 km = 2.77
miles
Final Crater Depth: 0.464 km = 0.288 miles
The crater formed is a complex crater.
The volume of the target melted or vaporized is 0.0236
km3 = 0.00565 miles3
Roughly half the melt remains in the crater, where its
average thickness is 2.14 meters = 7.04 feet
Thermal Radiation:
At this impact velocity ( < 15 km/s), little vaporization
occurs; no fireball is created, therefore, there is
no thermal radiation damage.
Seismic Effects:
The major seismic shaking will arrive at approximately
200 seconds.
Richter Scale Magnitude: 6.6
Mercalli Scale Intensity at a distance of 1000 km:
Nothing would be felt. However, seismic
equipment may still detect the shaking.
Ejecta:
The ejecta will arrive approximately 494 seconds after
the impact.
At your position there is a fine dusting of ejecta with
occasional larger fragments
Average Ejecta Thickness: 1.75 micrometers = 0.0688
1/1000 of an inch
Mean Fragment Diameter: 61.6 micrometers = 2.43 1/1000
of an inch
Air Blast:
The air blast will arrive at approximately 3030 seconds.
Peak Overpressure: 539 Pa = 0.00539 bars = 0.0765 psi
Max wind velocity: 1.27 m/s = 2.84 mph
Sound Intensity: 55 dB (Loud as heavy traffic)
Forrest M. Mims III 
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