Asteroids - those millions of chunks of space rock,
large and small, that drift and spin across our solar system - hold promise for
space explorers even as they pose a threat to us on Earth.
When NASA Administrator Charles Bolden discussed the
U.S. space agency's proposed 2014 budget with lawmakers in late April, he
highlighted a new mission - a plan to capture an asteroid in deep space and
bring it to the vicinity of the moon, where astronauts could later explore it.
"We are developing a process or technology that
will come forward in the asteroid retrieval mission that will demonstrate that
humans can, in fact, alter the path of an asteroid that's headed toward
Earth," he said.
A key part of the planned mission, Bolden underscored,
is to show that an asteroid's path can be diverted.
Asteroid Threats
Earlier this year, a small meteor unexpectedly
exploded over Chelyabinsk, Russia, and produced a shockwave that shattered
thousands of windows and injured more than 1,000 people. The same day, a
well-tracked, 45-meter-wide asteroid called 2012 DA14 whizzed safely past
Earth, closer than our geosynchronous satellites. It was a record close approach
for something that size.
Experts say asteroids larger than 100 meters across
strike the Earth's surface, on average, about once every 10,000 years, and
there are no records of an asteroid killing anyone in modern history.
John Holdren, the U.S. president's assistant for
science and technology, discussed asteroid threats at a hearing on Capitol Hill
in March. He told lawmakers that given the rarity of large asteroid impacts,
the potential loss of human life from such an event works out to fewer than 100
people per year, which he compared to 5 million deaths each year from tobacco.
"It doesn't look like a very big threat,"
Holdren said. "But, of course, that is not really a meaningful way to
present a risk of this character, where you're talking about a low probability
of a very big disaster, and in those sorts of situations, we tend to invest in
insurance to reduce the likelihood of a disaster we would regard as
intolerable."
Insurance, of course, was not an option for dinosaurs,
which are believed to have been killed off 65 million years ago after a
10-kilometer-wide asteroid crashed into the Earth.
Holdren says an asteroid even a fraction of that size
could undo life as we know it. "A one-kilometer asteroid would be carrying
energy in the range of tens of millions of megatons. That is as much or
more energy as was in the combined arsenals of the United States and the Soviet
Union at the height of the Cold War," he said. "An asteroid of that
size, a kilometer or bigger, could plausibly end civilization."
Tracking Asteroids
NASA estimates it has catalogued 95 percent of
near-Earth asteroids that are wider than one kilometer. It says it has found
nothing this size that poses a threat to our planet in the foreseeable future.
The space agency is now working to detect and track
much smaller near-Earth objects, ones that are 140 meters in diameter or
larger. The goal is to identify 90 percent of those by 2020.
That's where Lindley Johnson comes in. He is the
program executive for the Near-Earth Objects Program at NASA headquarters in
Washington. His office coordinates NASA-sponsored efforts to detect and track
potentially hazardous asteroids, as well as comets.
"The first and most important thing, of course,
is having the capability to find them early," Johnson explained. "You
can't do anything about them unless you know that there is one out there that
is a threat. So, that's our primary emphasis - finding them. If we do that job
well, then the incidence of us actually being impacted are pretty
rare."
International Cooperation
Johnson was among hundreds of scientists who attended
a United Nations conference on outer space in Vienna earlier this year. His
working group recommended creating an international asteroid-warning network
and a forum that brings various space agencies together to discuss
collaborative approaches to counter dangerous asteroids.
Johnson said they also recommended bolstering disaster
response, so national and international agencies could warn people about a
potential strike, just as they do about hurricanes or tsunamis. Part of the
reason people were injured in Chelyabinsk, he said, is that they did not know
what to expect.
"They didn't realize that with a meteor coming in
like that, that there would be such a shockwave that windows would be broken
out, so they saw the bright flash and ran to the window and were looking at the
contrail when the shockwave hit," he said.
As of late April, nearly 10,000 near-Earth objects had
been discovered, with about 1,400 of them classified as potentially hazardous.
Funding for NASA's Near-Earth Objects Program is about
$20 million per year, reflecting a five-fold increase during President Barack
Obama's administration.
Sources :
http://www.voanews.com/content/nasa-technology-asteroids-danger-space/1652690.html
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