[meteorite-list] Asteroid 2004 MN4: A Really Near Miss!

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Feb 4 19:32:56 2005
Message-ID: <200502050032.QAA11268_at_zagami.jpl.nasa.gov>

http://skyandtelescope.com/news/article_1458_1.asp

Asteroid 2004 MN4: A Really Near Miss!
By Alan M. MacRobert
Sky & Telescope
February 4, 2005

If you plan to be alive on April 13, 2029, you can
look forward to an asteroid-watching party across three continents like
nothing the world has ever seen.

The near-Earth asteroid 2004 MN4 made headlines for a couple of
days last December when astronomers estimated that it had a 1-in-38
chance of hitting Earth in 2029. The threat quickly passed when old
images were found that pinned down the asteroid's orbit well enough to
guarantee that it will miss our planet. Now, extremely precise radar
observations made on January 27th, 29th, and 30th have refined its orbit
even further. The asteroid is still certain to miss Earth, but it will
be a squeaker indeed - and the event will present a once-in-a-millennium
naked-eye asteroid show.

Paul Chodas, Steve Chesley, Jon Giorgini and Don Yeomans of NASA's Near
Earth Object Program calculate that the asteroid will pass 4.7 Earth
radii (30,000 kilometers, or 18,600 miles) from Earth's surface. This is
half the distance predicted by the previous orbit. The object should
brighten to magnitude 3.3 (similar to the faintest star in the Big
Dipper) while moving northwest across Sextans and Cancer at a speed up
to 42? per hour. Europe, Africa, and Asia will have the ringside seats.
With a newly estimated diameter of 320 meters, 2004 MN4 will appear up
to 2 arcseconds wide, making it barely resolvable in amateur telescopes.

The Americas will get their best view hours earlier, while the asteroid
is still on its way in and only 7th magnitude. The next night it will be
much fainter than this and near our line of sight to the Sun.

The radar observations were made by Lance Benner, Mike Nolan, Steve
Ostro, and Jon Giorgini using the giant Arecibo dish in Puerto Rico.
It's a good thing the refined orbit is still a miss: the impact energy
would be about 850 megatons, 15 times more powerful than the largest
hydrogen bomb ever tested and about 60 times more powerful than the
Tunguska explosion over Siberia in 1908. According to Chodas and his
colleagues, "On average, one would expect a similarly close Earth
approach by an asteroid of this size only every 1,300 years or so."

Mark your calendar, and if you're on the wrong side of the world, plan
on a vacation to join the party.

Further information is on NASA's Near Earth Object Program page:
http://neo.jpl.nasa.gov/news/news149.html .
Received on Fri 04 Feb 2005 07:32:42 PM PST