[meteorite-list] Nuclear Blasts Proposed for Warding Off Menacing Asteroids

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 17 Feb 2009 16:28:32 -0800 (PST)
Message-ID: <200902180028.QAA02583_at_zagami.jpl.nasa.gov>

http://www.mercurynews.com/breakingnews/ci_11717387?nclick_check=1

Nuclear blasts proposed for warding off menacing asteroids
By Suzanne Bohan
Contra Costa Times
February 17, 2009

After a 200-foot-wide meteorite sped toward the ground near the Tunguska
River in 1908, it unleashed an explosion in the remote Russian region
500 times more powerful than the bomb dropped on Hiroshima. The blast,
called the Tunguska Event, was detected in London by monitoring
equipment, and it leveled millions of trees over an 830-square-mile area.

Had the meteorite hit a populated area such as London, the result would
have been a catastrophe.

It's that rare but plausible scenario of a large meteorite striking an
increasingly crowded Earth that has a network of scientists, including
David Dearborn of Lawrence Livermore Laboratory, devising strategies to
monitor and then thwart these celestial menaces.

Dearborn, a research physicist, spoke at three free seminars Saturday in
Livermore, describing his strategy for using nuclear blasts to prevent
devastating meteorite strikes on Earth.

Throughout the ages, asteroids circling the sun have intersected Earth's
orbit and entered the atmosphere. Most of them are so small they quickly
burn up in a blaze, giving us a brief glimpse of their final moments,
which we call shooting stars. But about every 500 to 1,500 years,
Dearborn said, larger ones the size of the Tunguska meteorite reach
Earth. And every year, smaller ones carrying a lesser but still potent
punch get through, although most hit the ocean or remote terrestrial
regions.

"It's not uncommon," he said.

And sometimes they do hit populated areas, Dearborn added. "Cars have
actually been hit by meteorites."

When they hit, these cosmic bodies leave "impact craters" or can create
tsunamis if they land in the ocean. There are about 170 known impact
craters, including the 120-mile-diameter Chicxulub crater on the Yucat??n
Peninsula in Mexico, and many thousands that either eroded away or
remain undetected on land or the ocean floor. The huge meteorite
creating the Chicxulub crater struck 65 million years ago, and
scientists believe it brought about the extinction of the dinosaurs,
along with three-quarters of life on Earth, by radically altering the
atmosphere by kicking up clouds of dust and sulfur gases. An event that
size is expected every 50 million to 100 million years, the NASA stated.

Hundreds of thousands of asteroids form a belt that circles the sun from
Mars to Jupiter, and they range in size from less than a mile in
diameter to nearly 500 miles across. In the 1990s, scientists started
paying more attention to the dangers posed by this asteroid belt,
Dearborn said. Now about 4,500 of them are deemed "near-Earth objects"
that are likely to cross Earth's path at some point, or get dangerously
close.

Dearborn proposes sending spacecraft bearing nuclear explosives to an
asteroid identified as a threat by a NASA program called "Space Guard."
The program is tasked with tracking near-Earth asteroids larger than 1
kilometer. Congress asked NASA to create the program in 2005.

The nuclear blasts could change the speed of the asteroid enough to
prevent it from slamming into Earth, much like slowing down or speeding
up a car to stop it from striking another object.

Nuclear material has the advantage of packing far more energy into it
per ton than any comparable explosive material ??? a key consideration on
weight-conscious space missions, Dearborn said. Detractors of this
approach worry about the spread of radioactive material in space with
such a system, but Dearborn said it would be detonated so far out that
minuscule amounts - far less than that found naturally on Earth - would
reach the atmosphere. Others are leery of former weapons being used in
the neutral realm of outer space. NASA, however, in a 2007 report
described the use of nuclear blasts as the best approach for handling
threatening asteroids.

Other strategies under consideration include using a gravity tracker,
which could slightly alter an asteroid's trajectory by exerting on it
the gravitational pull of nearby spacecraft, although Dearborn said that
approach is marred by the enormous fuel requirements of such spacecraft.

Dearborn, however, pointed out that with the Space Guard program,
there's ample time to prepare for a threatening asteroid or comet, since
they can be detected decades in advance. "We'll have time to think about
all sorts of things," Dearborn said. What's most critical, he said, is
to maintain the monitoring system.

"With the warning, you have options."

For details on Dearborn's talk, "Avoiding Armageddon: Diverting
Asteroids With Nuclear Explosives," visit the Lawrence Livermore
Laboratory's "Science on Saturday" series, visit education.llnl.gov/sos
<http://education.llnl.gov/sos>.
Received on Tue 17 Feb 2009 07:28:32 PM PST