News in Science

Russian meteor's impact circled Earth, twice

Big boom When a meteor slammed into the atmosphere last February, it produced a powerful shock wave that blasted the city of Chelyabinsk, causing property damage and inflicting over 1500 injuries.

Now, an analysis of data gathered by global detectors using to detect ultra-low frequency acoustic waves, has revealed that the meteor's shock wave travelled all the way around the globe, twice.

The International Monitoring System (IMS) network operated by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) is used to detect infrasound evidence of nuclear tests. That February morning, the network detected the most powerful event it had ever seen.

But this signal wasn't a nuclear weapon, it was a high-speed, 10,000 tonne chunk of space rock carrying out a surprise attack on Russia.

"For the first time since the establishment of the IMS infrasound network, multiple arrivals involving waves that traveled twice round the globe have been clearly identified," writes Alexis Le Pichon, scientist of the Atomic Energy Commission, France, and his team in a paper that has been accepted for publication in the journal Geophysical Research Letters.

Le Pichon's team used data from 20 IMS stations around the globe to estimate the energy of the Chelyabinsk event.

"A preliminary estimate of the explosive energy using empirical period-yield scaling relations gives a value of 460 kilotons of TNT equivalent," they write. This means the Russia meteor delivered an equivalent energy of nearly 30 Hiroshima-sized atomic bombs in the skies over Chelyabinsk.

This IMS estimate confirms that this meteor strike is the largest impact since the 1908 Tunguska event that flattened 80 million trees over an area of 2150 square kilometres. That event, however, is estimated to have delivered 10-15 megatons of TNT equivalent to the atmosphere, generating an immensely powerful shock wave that caused chaos over a wide and, fortunately, sparsely populated area.

The Russian meteor, which was only 17 metres wide, quickly brought attention to the number of small asteroids that are out there, capable of remaining undetected and yet still deliver a shocking punch to a populated region.