The Chelyabinsk meteor that exploded over Russia this past February was much heavier than initially thought -- and similarly small asteroids might be headed our way more often than we previously thought, scientists say.
In a trio of papers dissecting the space rock published on Wednesday, scientists across the globe gathered both scientific data and personal accounts of the biggest impact from the sky since the Tunguska event in 1908. When it first entered Earth's atmosphere, the Chelyabinsk meteor weighed between 12,000 and 13,000 metric tons -- around twice as heavy as initial estimates. Luckily, no one was killed by the meteor, which exploded into gas, dust and a few small fragments nearly 17 miles above ground with the energy equivalent of 500 kilotons of TNT. At least 1,500 people were injured though as the result of shattered windows and building collapses stemming from a shockwave that spread out as far as 62 miles from its central point.
One of the other serendipitous things about the Chelyabinsk meteor’s fall to Earth was the plethora of cameras that recorded its journey, according to Peter Jenniskens of SETI (Search for Extraterrestrial Intelligence Institute). An astounding number of smartphone cameras, car dashboard cameras, and other devices captured the meteor’s explosive entry.
“The impact was so well observed -- we’re very thankful to all the people that filmed, it’s a real treasure trove,” Jenniskens said in a phone interview. “We think that Chelyabinsk is going to become the gold standard [for meteor impacts].”
In a paper published in Science on Wednesday, Jenniskens and colleagues examined the meteor’s composition, impact, and its potential history. Researchers think the rock originally came from the asteroid belt located between Mars and Jupiter due to both its mineral composition and the path it took through our solar system. The meteor was also likely a broken-off chunk from a much-larger rock that formed about 4.4 billion years ago. Jenniskens and his team also think it’s possible that the Chelyabinsk meteor had a previous close encounter with Earth about 1.2 million years ago. Back then, the tidal forces might have ripped its 20-meter-wide bulk off of another parent rock and set it on a later collision course with our planet.
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On a teleconference call with reporters, NASA officials noted that the agency doesn’t gauge near-Earth objects by size; they search for objects by brightness, and their ability to spot near-Earth objects gets better every year. Chelyabinsk, however, was a special case -- it rocketed toward our planet from the direction of the sun, making it effectively invisible to detection until it hit.
“Luckily, most of the kinetic energy [of Chelyabinsk’s explosion] was absorbed by the atmosphere,” Jiri Borovicka, an asteroid researcher at the Academy of Sciences of the Czech Republic and an author of one of the two Nature papers, told the journal’s news service. ”A more solid rock that might have blasted closer to the ground would have caused considerably more damage.”
The other meteor paper published in Nature, written by a team led by a University of Western Ontario astronomer, says the actual impact risk of Chelyabinsk-size asteroids may be much larger than previously assumed. While models suggest that asteroids 10 to 20 meters in diameter strike the Earth only about once every 150 years, when you actually look for signs of airbursts -- meteors exploding in our atmosphere -- they crop up more often than you might think.
“The residual impact risk -- from asteroids with yet-unknown orbits -- is shifting to small-sized objects,” Brown told Nature.
So what is to be done? NASA recently gave a $5 million grant to the University of Hawaii to kickstart an international asteroid warning system called Atlas. University of Hawaii astronomers are building up to eight telescopes that will sweep the night sky starting around 2015. Researchers estimate that Atlas could give a one-week warning for a 50-yard-wide asteroid, which could threaten a city, and a three-week warning for a 150-yard-wide asteroid. That lead time could give countries and cities time to evacuate people.
For any really big, extinction-event-level asteroids headed our way, humanity will have to get creative. A United Nations space advisory council also holds an annual competition seeking plans for moving large asteroids that might threaten the Earth. Last year's winner, Sung Wook Paek, proposed to shoot an asteroid with white paintballs that would increase an asteroid's reflectivity, thereby letting solar radiation do the work of pushing it away from Earth. The knowledge we glean from studying other impacts like the Chelyabinsk explosion will be invaluable to any future plans.
"If humanity does not want to go the way of the dinosaurs, we need to study an event like [Chelyabinsk] in detail," University of California Davis earth scientist Qing-Zhu Yin, one of the coauthors of the Science paper, said in a statement Wednesday.