The take home
is that we catch around two significant asteroids per year and that becomes a
two hundred object sample each century.
That really means that the threat level is plausibly comparable to
tsunami. This is significant. It is 10,000 objects in 500 years. Thus the chance of an impact causing serious
damage to a populated area is actually far higher than imagined.
It also means
that the ranges of imagined threats is also not zero or particularly close to
zero. Recall also that we have only been
gathering data mostly during the past two centuries with anything approaching a
global scale. This comforts us to the
extent of knowing the risk is low, yet I suspect that the risk really does
compare well to some known geological risks that we can identify and work
around.
Last year’s
nasty event was a sharp proof that the risk is real and we can now teach that
to our children instead of burying the concern in faux controversy.
Asteroids
Whack Earth More Often Than Thought
APR 22, 2014 02:30 PM ET // BY IRENE KLOTZ
A global network that listens for
telltale traces of nuclear weapons tests detected 26 explosions between 2000
and 2013 caused not by nuclear explosions but by asteroids blasting apart in
the atmosphere, a video visualization released on Tuesday shows.
Only one impact, the 2013 strike over
Chelyabinsk, Russia, caused widespread injuries and damages on the ground, but
the study is a somber reminder that Earth's lucky days may be numbered.
"Most of the impacts are too small and
too high up to cause major damage ... but it does show you ... an asteroid
large enough to destroy a city is likely to occur about once every century or
so," Ed Lu, a former NASA astronaut who now oversees the asteroid-hunting
B612 Foundation, told reporters on a conference call.
"There is a popular misconception that
asteroid impacts are extraordinarily rare -- millions of years between large
asteroid impacts -- and that's incorrect. We think that actually seeing these
things on a map, on a globe of the Earth with the date will help them
understand that," Lu said.
The data used in the video was collected by
a global network of infrasound stations, consisting of microbarometers that
continuously measure miniscule changes in air pressure at frequencies much
lower than the range of human hearing. The network is operated by the Nuclear
Test Ban Treaty Organization.
The B612 Foundation -- named after a
fictional planet in the book The Little Prince by French author and pilot
Antoine de Saint-Exupery -- plans to launch a telescope in 2018 to scope out
potentially dangerous asteroids, such as the one that exploded over Chelyabinsk
with the force of 600 kilotons of energy. More than 1,000 people were injured
by flying glass and debris.
In comparison, the atomic bomb dropped on
Hiroshima in 1945 had an energy impact of 15 kilotons.
During its initial 5.5 years of operation,
B612's telescope, called Sentinel, should be able to find 90 percent of
near-Earth asteroids 460 feet (140 meters) in diameter or larger, and about 50
percent of asteroids 130 feet (40 meters) in diameter.
Asteroids between 40 and 45 meters in
diameter are the ones that have the potential to destroy a city.
"Picture a large apartment building
-- moving at Mach 50," Lu told Discovery News.
"Chelyabinsk taught us that asteroids
of even 20-meter size can have substantial effect. The size range of what you
would call a 'city-killer' is beginning to decrease," Lu said.
"The data we have is just on the edge
of what's just large enough to destroy a city, but this is not the main point
... Whether or not these things happen once a century, once every 80 years or
once every 150 years, we're going to find out once we launch Sentinel.
"What's important is that people need
to understand that it's not once in million years, it's not once every 50
million years. It's not super-duper rare," Lu said.
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