Two big space rocks, two close calls, within 24 hours: The large meteor
that burned up over northern Russia Thursday surprised everyone, while
Friday's close fly-by of a 150-foot-long asteroid was discovered less
than a year ago. Suddenly, a scenario for a Michael Bay movie is that
much closer to reality and is sparking discussions about tracking and
defending threats from space.
A blazing meteor streaked across the skies of Russia on Thursday,
leaving a large smoke trail in its wake before blowing up over the
remote town of Chelyabinsk in the Ural mountains. More than 1,000 people
reported injuries, and windows across the region were shattered by a
deafening sonic boom.
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| A meteor seen flying over Russia on Feb. 15 at 3:20:26 UTC impacted Chelyabinsk. Preliminary information is that this object was unrelated to asteroid 2012 DA14, which made a safe pass by Earth today. (Image credit: Google Earth, NASA/JPL-Caltech) |
On Friday, a 150-foot-wide asteroid named 2012 DA14 whizzed by the Earth
with just over 17,000 miles of separation to spare. That makes it the
closest approach ever to the planet for a space rock of that size.
The two celestial events were not connected, NASA said; they
approached the Earth from different trajectories. Yet they are just two
of several meteors and asteroids that have come close to the Earth in
the past few years.
There are between 3,200 and 4,700 potentially hazardous asteroids in
our solar system, NASA estimated. This week's sky shows, while
fascinating to watch, have spurred discussions about whether the system
for detecting potentially dangerous meteors and asteroids is adequate --
and if not, what is being done about it.
More on the Chelyabinsk Meteor
The meteor that exploded over Chelyabinsk was the largest reported since
1908, when one hit Tunguska in Siberia. It entered the atmosphere at
about 40,000 mph, or 18 km per second, NASA said, and released several
hundred kilotons of energy.
The meteor measured about 49 feet and had a mass of about 7,000 tons.
It was brighter than the sun, and its trail was visible for about 30
seconds. It had a very shallow angle of entry.
The meteor might have exploded because it was either big or dense
enough that it didn't burn up entirely in the atmosphere, but still
experienced "immense aerodynamic pressures [that were] enough to
structurally deform it," said Ben Corbin, a Ph.D. candidate in
aeronautics and astronautics at the
Massachusetts Institute of Technology. "It's simply a matter of how much energy is getting displaced at once."
If the meteor had hit a densely populated area, it could have taken
out an entire city, William Newman, professor of earth and space
sciences at the
University of California at Los Angeles, told TechNewsWorld.
Blind Man's Bluff
The other big space rock to make the news, 2012 DA14, was discovered on
February 23, 2012, and has been tracked closely since then. That raises
the question of why the Chelyabinsk meteor seemed to have come out of
nowhere.
One reason: The Chelyabinsk meteor was too small, being about 1.5
meters on a side, whereas 2012 DA14 "is about half the size of a
football field," Newman said. "It's possible to see a railroad car
heading towards us at a distance, but it's impossible to see a baseball
or bullet heading our way."
Asteroids that cross the Earth's orbit are only visible in daytime, so
they're harder to observe than those outside Earth's orbit, Corbin told
TechNewsWorld. They can be detected with radar, but that technology can
only be used to find objects when they're very close, because radar
waves have to be bounced off the subject.
NASA maintains a database of asteroids that could impact the planet as part of its Near Earth Object program.
The program "is able to detect about 90 percent" of the larger
asteroids that could impact Earth, and "we're getting to the point where
we'll be able to detect almost all of those," Newman said.
A Future Early Warning System?
The Chelyabinsk meteor shows the need to set up spacecraft circling the
Earth to intercept and evaluate incoming threats, argued Rick Tumlinson,
chairman of
Deep Space Industries, which plans to mine asteroids for their precious metals.
The company is working on the FireFly spacecraft that would begin
prospecting for potential target asteroids in 2015, and the larger
Dragonfly spacecraft that would do the actual mining work.
Placing a circle of 10 Fireflies around the planet would cost about
US$100 million and take about four years, Tumlinson estimated.
"We're talking about space budgets," Tumlinson told TechNewsWorld.
"The idea is to send out the Fireflies to take close-up shots, then for
the Dragonflies to come back with samples so they can be analyzed. By
2021, we can make contact with the asteroids and figure out which ones
can be mined safely, and which will need to have their orbits shifted so
they don't threaten Earth."
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