Xinhua | 2013-11-7 | Global Times
Researchers from Russia, US, China and several other countries on Wednesday released details of the asteroid that exploded violently above the Russian city of Chelyabinsk in February this year, calling it “truly a wake-up call” for the world.
“There are only less than one percent of Chelyabinsk-sized objects out there being documented, meaning more than 99 percent of similar objects which can give a populated region a bad day remain undetected,” Qing-Zhu Yin, professor of the University of California, Davis, who participated in analyzing the event, told Xinhua.
“If the humanity does not want to become dinosaurs, we need to study this kind of object in details,” Yin said.
Chelyabinsk was one of the largest meteoroid strikes since the Tunguska event of 1908, and thanks to modern consumer electronics, field sensors and advanced laboratory techniques available nowadays, provides an unprecedented opportunity to study such an event, the researchers reported.
The study, published in the journal Science, was led by Olga Popova of the Russian Academy of Sciences in Moscow, and by US astronomer Peter Jenniskens, join by researchers from China and eight other countries.
The researchers visited 50 villages around Chelyabinsk in the weeks that followed the violent airburst and collected data on the asteroid that caused it as well as the damage it caused. They also used security cameras and dash-cams in peoples’ cars to re-trace the fireball’s path through the sky.
Based on their study, they determined that the asteroid was originally 19.8 meters wide, although it left a hole just 7 meters wide in the ice where it landed and that the weight before entering the atmosphere was 13,000 tons.
After entering atmosphere, it exploded several times as it was descending, starting at 83 km, 54 km, 29.7 km, and finally at 27 km, and reached its brightest and hottest point at an altitude of about 30 km, when it was traveling at about 18.6 km per second, or 50 times faster than a bullet, the researchers said.
The researchers also estimated that the total energy of the event, which shattered thousands of windows in Chelyabinsk, was the equivalent to an explosion of around 600,000 tons of TNT.
“Much of the materials were evaporated in the atmosphere thankfully, and causing less damage on the ground. And the final mass landed on were estimated to be 4000-6000 kg only, with the largest single stone at about 650 kg excavated the Chebarkul lake bed,” Yin said.
“The ground damage area due to the blast wave is estimated to be 6000 km2. The shape of the damaged area on the ground looks like a butterfly,” he said.
The Chelyabinsk meteorite belongs to the most common type of meteorite, an “ordinary chondrite”. If a catastrophic meteorite strike were to occur in the future, it would most likely be an object of this type, Yin said.
Chemical and isotopic analysis confirmed that the object was 4, 452 million years old, and that it last went through a significant shock event about 115 million years after the formation of the solar system 4,567 million years ago. That impact was at a much later date than in other known chondrites of the same type, Yin said, suggesting a violent history.
Meanwhile, two papers in the British journal Nature on Wednesday said the orbit of the Chelyabinsk asteroid seems to be similar to another asteroid that has orbited close to Earth, the 2- km-sized asteroid 1999 NC43, suggesting that the two were probably once part of the same object. The papers also predicted that the estimated damage for the tens of meter-sized objects like Chelyabinsk were actually ten times greater than previously thought.
Yin noted that major meteorite strikes like Tunguska or Chelyabinsk occur more frequently than we tend to think. For example, four tons of material were recovered from a meteor shower in his hometown, Jilin, China in 1976.
“Chelyabinsk is a violent reminder,” Yin said. “Our hope is by documenting what they are made of, and what kind of threat they pose through such a detailed, internationally collaborative study, to serve as ‘poster child’ for developing future asteroid impact mitigation strategies for our children and children’s children.”