


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.

But 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.


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.




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No word that it caused an EMP - if a nuclear bomb explodes high in the ionosphere, it causes an electromagnetic pulse that can destroy electronics etc.  Apparently meteors can do this too. 

The Washington Post:  "Videos posted on Web sites recorded a cacophony of shattering glass, hundreds of car alarms and a considerable amount of swearing ..."

Sounds very Russian :)

Yes apparently one Russian politician claimed the U.S. was testing a new weapon. 

There was a giant hole in the ice where the exploded parts of the meteor went in. 

Apparently it was detected by Comprehensive Test Ban Treaty sensors, which watch for nuclear explosions. 

I wouldn't expect it to have; those result from very energetic electromagnetic pulses (gamma rays, X rays) that you can't get from this sort of event.

I'm not sure, EMP's can be generated in non-nuclear ways.  A meteorite striking a satellite can cause a small EMP apparently.  Also a big solar storm could cause a big destructive EMP by suddenly changing the magnetic field.

Apparently it exploded below the ionosphere, though.

On the one hand, we can't detect the small stuff until too late (not that we really have the capability yet), and there's a lot of it.  On the other hand, because it is fairly common, we have a pretty good idea how commonly the small stuff hits; we have a fairly good statistical sample.  And yes it will absolutely happen again; this sort of thing is if I understand correctly a once every few years thing.  (It's unusual to hit near a sizeable city though; most of the earth is not urbanized.)

The scary stuff--dinosaur killers, and Tunguska events that COULD flatten cities if they happened close by--we have a much worse feel for, both intuitively and statistically.

The Tunguska event in 1908, by the way, missed wiping out the capital of the Russian Empire by about eight hours.  It hit at 60.886°N, 101.894°E, and a few hours later the earth would have rotated far enough to put St. Petersburg (then the capital of Russia) under (it would have missed by maybe 40 miles, since st. pete is just barely south of 60 N)

Now THAT would be an interesting alternate history plot--1908 and St. Petersburg is annihilated mysteriously (we had no concept of nukes back then) and one of the great European powers is decapitated.  (I should mail that one off to Harry Turtledove...)

When Mt St Helens blew, the devastation overwhelmed my imagination. For the first time I could understand the Tunguska event and those photos of knocked over forests. I didn't know St Petersburg came that close to destruction.

It was thousands of miles away actually... but at almost the same latitude, so if the thing had come a few hours later, and the earth had rotated to put St. Pete's where Tunguska had been--WHAM!

Lillie, isn't it exciting to be able to participate in life and be witness to the incredible diversity that exists! Each minute is precious.



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