16 February 2013: 
The meteor that exploded over Russia Friday was slightly larger than previously thought and more powerful, too, NASA scientists say.
The Russian meteor explosion over the city of Chelyabinsk, on Friday (Feb. 15), injured more than 1,000 people and blew out windows across the region in a massive blast captured on cameras by frightened witnesses. Friday afternoon, NASA scientists estimated the meteor was space rock about 50 feet (15 meters) and sparked a blast equivalent of a 300-kiloton explosion. The energy estimate was later increased to 470 kilotons.
But late Friday, NASA revised its estimates on the size and power of the devastating meteor explosion. The meteor's size is now thought to be slightly larger — about 55 feet (17 m) wide — with the power of the blast estimate of about 500 kilotons, 30 kilotons higher than before, NASA officials said in a statement. [See video of the intense meteor explosion]
The meteor was also substantially more massive than thought as well. Initial estimated pegged the space rock's mass at about 7,000 tons. Scientists at NASA's Jet Propulsion Laboratory in Pasadena, Calif., now say the meteor weighed about 10,000 tons and was travelling 40,000 mph (64,373 km/h) when it exploded.
"These new estimates were generated using new data that had been collected by five additional infrasound stations located around the world - the first recording of the event being in Alaska, over 6,500 kilometers away from Chelyabinsk," JPL officials explained in the statement. The infrasound stations detect low-frequency sound waves that accompany exploding meteors, known as bolides.
The meteor entered Earth's atmosphere and blew apart over Chelyabinsk at 10:20 p.m. EST on Feb. 14 (03:20:26 GMT on Feb. 15). The meteor briefly outshined the sun during the event, which occurred just hours before a larger space rock — the 150-foot-wide (45 meters) asteroid 2012 DA14 — zoomed by Earth in an extremely close flyby.
Asteroid 2012 DA14 approached within 17,200 miles (27,000 kilometers) of Earth Friday, but never posed an impact threat to the planet. The asteroid flyby and Russian meteor explosion had significantly different trajectories, showing that they were completely unrelated events, NASA officials said.
Late Friday, another fireball was spotted over the San Francisco Bay Area in California. That event, also unrelated, occurred at about 7:45 p.m. PST (10:45 p.m. EST/0345 Feb. 16 GMT) and lit up the nighttime sky. Aside from the unexpected light show, the fireball over San Francisco had little other effect.
NASA scientists said the Russian meteor event, however, is a rare occurrence. Not since 1908, when a space rock exploded over Russia's Tunguska River in Siberia and flattened 825 square miles (2,137 square km) of uninhabited forest land, has a meteor event been so devastating.
"We would expect an event of this magnitude to occur once every 100 years on average," Paul Chodas of NASA's Near-Earth Object Program Office at JPL said. "When you have a fireball of this size we would expect a large number of meteorites to reach the surface and in this case there were probably some large ones."
According to the Associated Press, search teams have recovered small objects that might be meteorite fragments and divers are searching the bottom of a lake where a meteorite is thought to have landed.
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Related Article:Asteroid Passes Earth as UN Mulls Monitoring Network
Mark Drajem & Alexander Weber - Bloomberg
Feb 16, 2013 : An asteroid half the size of a U.S. football field passed within an astronomical hair’s breadth of Earth today in the closest such encounter in a century.
The asteroid, called 2012 DA14, came within 17,200 miles (27,350 kilometers) of Earth at 2:25 p.m. Washington time, over Indonesia. Telescope images from western Australia, broadcast on NASA Television, showed the asteroid as a white speck against the blackness of space.
While DA14 didn’t hit the planet, astronauts and interplanetary evangelists say its fly-by -- and a meteor strike in Russia early today -- serve as evidence that monitoring for risks from space objects must be increased.
“If this asteroid were to hit London, the entire metropolitan area would be gone,” Sergio Camacho, head of the effort at the Vienna-based UN Office for Outer Space Affairs, said of DA14 in an interview.
Camacho’s “Action Team on Near-Earth Objects” is set to propose a global asteroid warning network, which would discover, monitor and characterize the risks of those orbiting objects. The group also suggests a team to oversee a space mission to deflect or blow up an asteroid headed for Earth.
An asteroid of a similar size slammed into rural Russia in 1908 and leveled millions of trees over 820 square miles. The asteroid scientists say plowed into Earth about 66 million years ago, wiping out the dinosaurs, was about 6 miles in diameter.
Meteor Detection
Other space objects, such as the meteor that slammed into Russia’s Urals region today and caused hundreds of injuries, couldn’t be detected with existing telescopes, said Detlef Koschny, a scientist at the European Space Agency who is also part of the UN working group.
“The goal is that we can see objects this size about two days before they hit the Earth,” he said today in a telephone interview. Information on those smaller objects should also eventually be part of a UN global database, he said.
In 1998, the U.S. space agency NASA began working on finding and tracking the largest asteroids, typically more than one kilometer in diameter and capable of destroying much of humanity. That’s left a big gap in finding smaller objects that would demolish a city while sparing the rest of civilization.
NASA says it has found and mapped 1,310 of the largest, most dangerous “near-Earth objects.” The total may account for less than 10 percent of all space threats, it says.
‘Resources, Funding’
“The whole field needs more resources and funding,” Bruce Betts, director of projects at the Pasadena, California-based Planetary Society, founded in 1980 by Carl Sagan to promote space exploration, said in an interview.
In 2008, a group of former astronauts submitted a report to the UN working group, urging a global response to asteroid threats. “Questions arise regarding the authorization and responsibility to act, liability, and financial implications,” the Association of Space Explorers wrote in the paper.
In its final report, the UN group proposes an international asteroid warning network to be a clearing house for all observations of near-Earth objects, the technical term for asteroids in close vicinity to the planet.
DA14 was discovered in February 2012 by a group of amateur astronomers at La Sagra Observatory in southern Spain. Jaime Nomen, a dental surgeon who dabbled in astronomy, said his group bought a high-powered telescopic camera and software with the help of a $7,695 grant in 2010 from the Planetary Society.
The probability of an asteroid hitting Earth is fairly low.
Evacuation Option“If we’re lucky, none of us will see an asteroid coming toward the Earth in our lifetime,” Camacho said. “But if we’re not lucky and we didn’t do anything, the only thing we might be able to do is evacuate.”
“This alone could be a disastrous event.”An asteroid on course to hit Earth can be deflected with a spacecraft, redirected with a “gravity tractor” hovering nearby or, as a last resort, targeted with a nuclear explosion.
In the meantime, bureaucracy needs to work at its pace. The UN group’s recommendations must be endorsed by the General Assembly, which Camacho expects will consider it when it meets in New York in October.
For some asteroids, there could be 20 to 30 years until the threat becomes imminent, Camacho said. “But we could find one that would give us three months.”
Koschny said the asteroid and meteor encounters should help the UN group’s cause: “This shows that we are doing something that should be taken seriously. It’s not only something a crazy scientist came up with.”