www.mashable.com/2013/02/16/asteroid-attack/


The world will have to live with
surprise asteroid attacks on the scale
of Friday's Russian fireball, at least for
a while.
The meteor that exploded over the
Russian city of Chelyabinsk
without warning Friday (Feb. 15),
damaging hundreds of buildings and
wounding more than 1,000 people,
was caused by a space rock about 50
feet (15 meters) wide, researchers
said.
Asteroids of this size are both difficult
to detect and incredibly numerous, so
it will take a long time for
astronomers to find and map out the
orbits of all the potentially dangerous
ones. Besides, researchers have
bigger fish to fry.
"Defending the Earth against tiny
asteroids such as the one that passed
over Siberia and impacted there is a
challenging issue that is something
that is not currently our goal," Paul
Chodas, a scientist with the Near Earth
Object Program Office at NASA's Jet
Propulsion Laboratory in Pasadena,
Calif., told reporters Friday (Feb. 15).
[Meteor Blast Over Russia Feb. 15:
Complete Coverage
]
"We are focusing on the larger
asteroids first," Chodas added. "They
are the ones that are the most
hazardous."
Millions of asteroids
In 1998, Congress directed NASA to
find all of the near-Earth asteroids at
least 0.6 miles (1 kilometer) wide that
could pose an impact risk to Earth.
Such large space rocks have the
potential to end human civilization if
they hit us.
NASA met that challenge several years
ago, and its scientists have now
identified 95 percent of the 980 such
mountain-size asteroids thought to be
cruising through Earth's
neighborhood. Happily, none of the
known behemoths pose any threat to
our planet for the foreseeable future.
The outlook isn't so rosy for smaller
asteroids.
Observations by NASA's WISE space
telescope, for example, suggest that
about 4,700 asteroids at least 330 feet
(100 m) wide come uncomfortably
close to our planet at some point in
their orbits. To date, astronomers
have detected less than 30 percent of
these objects, which could destroy an
area the size of a state if they
slammed into Earth.
And researchers have spotted less
than 1 percent of asteroids at least
130 feet (40 m) wide, according to
officials with the B612 Foundation, a
nonprofit organization dedicated to
predicting and preventing catastrophic
asteroid strikes.
Space rocks of this size can cause
severe damage on a local scale, as the
1908 "Tunguska Event" shows. That
year, a 130-foot-wide object exploded
over Siberia's Podkamennaya
Tunguska River, flattening roughly 825
square miles (2,137 square km) of
forest.
A space rock in this size class gave
Earth a close shave Friday. The 150-
foot-wide (45 m) asteroid 2012 DA14
— which was just discovered in
February 2012 — cruised within
17,200 miles (27,000 km) of our
planet, marking the closest approach
of such a big space rock that was ever
predicted in advance.
Overall, scientists think 1 million or
more near-Earth asteroids are lurking
out there, and just 9,600 have been
identified to date.
Improving the search
Searching near-Earth space in infrared
wavelengths is a good way to find
potentially hazardous asteroids,
Chodas said, and many other
scientists agree.
The B612 Foundation, in fact, plans to
launch an infrared space telescope
called Sentinel to a Venus-like orbit in
2018. From there, the instrument
would peer out toward Earth's
neighborhood without having to
contend with the sun's overwhelming
glare.
In less than six years of operation,
Sentinel should spot 500,000 near-
Earth asteroids, including the few
remaining undetected mountain-size
space rocks and more than 50 percent
of the 130-footers, B612 officials have
said. The goal is to find big,
dangerous objects several decades
before they may hit us, giving
humanity enough lead time to mount
a deflection mission.
But even if Sentinel lives up to its
billing, many thousands of 130-foot
asteroids would remain undetected,
as would even more objects the size
of the Russian fireball's parent body.
So we're likely to be caught off guard
again, as the people of Chelyabinsk
were Friday.
"NASA has recognized that asteroids
and meteoroids and orbital debris
pose a bigger problem than anybody
anticipated decades ago," said Bill
Cooke, head of NASA's Meteoroid
Environment Office at Marshall Space
Flight Center in Huntsville, Ala.