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Researchers reveals Earth is more vulnerable to giant asteroid blasts than previously thought

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Posted November 27, 2013

The 10,000-ton meteor that burst over the Russian city of Chelyabinsk earlier this year at 40,000 miles per hour shocked the inhabitants of the region and left scores of injuries and broken windows in its wake.

But, as reported in explorations now magazine earlier this year the massive scale of the event represented a boon to scientists at Scripps Institution of Oceanography at UC San Diego who monitor earth processes across several disciplines.

Nature's featured cover research on the Chelyabinsk meteor includes Scripps researchers.

Nature’s featured cover research on the Chelyabinsk meteor includes Scripps researchers.

And now that information is paying dividends, most recently in a new study published in the journal Nature that describes in detail the size and scale of the colossal fireball, which was approximately 17 meters (55 feet) wide and delivered an explosion estimated to be on par with 500 kilotons of TNT.

The international team of scientists have shown that Earth is vulnerable to being hit with more Chelyabinsk-sized meteors in the future than previously thought.

The Scripps researchers, including Luciana Astiz, Catherine de Groot-Hedlin, Michael Hedlin, and Gabi Laske, contributed to the study by helping to pin down the location and yield of the main explosion.

“During the time of atmospheric nuclear testing much work was done on estimating the size (explosive yield) of a large above-ground test from the seismic surface waves it excited. We drew on this work to estimate the explosive yield of the Chelyabinsk meteor,” said Michael Hedlin, a research geophysicist at Scripps. “We further analyzed the seismic data to estimate where (geographic and altitude) sound energy came from.”

The time of the source of the surface waves was about 84 seconds after the main flash reported by other sensors, said Hedlin, head of the Laboratory for Atmospheric Acoustics at Scripps, one of the institution’s efforts in long-term observations that deliver valuable data for science and society.

“This gave an altitude estimate of 29 kilometers (18 miles),” he said. “All geographic locations we obtained lay close to the ground track of the meteor but slightly to the north.”

The arrival times of secondary sonic booms heard on videos were also used to locate fragmentation points, and to calculate that the asteroid broke into small pieces between around 30 and 45 kilometers (18.6 and 27.9 miles) above the ground. At peak brightness, the bursting meteor appeared to be 30 times brighter than the sun.

The research team, which included the University of Western Ontario’s Peter Brown, Margaret Campbell-Brown, Paul Wiegert and David Clark, showed that existing models for estimating airburst damage for the circumstances of the Chelyabinsk impact do not match observations. They suggest that the number of objects with diameters in the range of tens of meters that impact the Earth may be several times greater than previously thought.

“Existing models predict events like the Chelyabinsk asteroid might hit every 120 or 150 years, but our data shows the frequency may be closer to every 30 or 40 years,” said Peter Brown. “That’s a big surprise. When Chelyabinsk happened, I would have never expected to see an event big enough to cause damage on the ground. It’s totally outside the realm of what we thought likely in our lifetimes based on earlier statistics. Our statistics now suggest this type of event likely happens with more frequency.”

According to the study, the orbit of the Chelyabinsk asteroid seems to be similar to another asteroid that has orbited close to Earth – the near-Earth asteroid 86039 (199 NC43) – suggesting that the two were probably once part of the same object.

Source: Scripps Institution of Oceanography

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