When the Chelyabinsk meteor exploded high over Russia on February 15, it was a blast heard around the world. This isn't just a figure of speech. Though too low-frequency for human hearing, sound waves from the 500-kiloton detonation of the 17-meter (56-ft) rock were picked up in Antarctica – some 15,000 km (9,320 miles) away – by 17 Comprehensive Test Ban Treaty Organisation (CTBTO) infrasound stations dedicated to detecting nuclear explosions above or below ground.
The Chelyabinsk meteor was the largest space object to explode on Earth in over a century. It was captured on dramatic videos, knocked down walls, blew in windows and injured about a thousand people as it released as much energy as 30 Hiroshima atomic bombs. It also set off infrasonic waves – sub-audible sounds between 0.001 Hz and 20 Hz. These can travel around the world and are used by the CTBTO’s network of 45 infrasound stations to help enforce treaties against nuclear testing.
According to the CTBTO, the Chelyabinsk meteor was the largest event ever recorded by its network.
“We saw straight away that the event would be huge, in the same order as the Sulawesi event from 2009,” said CTBTO acoustic scientist, Pierrick Mialle. "The observations are some of the largest that CTBTO’s infrasound stations have detected."
The Sulawesi event was the explosion of a bolide meteor over Indonesia, which was recorded by 15 CTBTO stations.
“We know it’s not a fixed explosion because we can see the change in direction as the meteorite moves towards the earth" added Mialle. "It’s not a single explosion, it’s burning, traveling faster than the speed of sound. That’s how we distinguish it from mining blasts or volcanic eruptions. Scientists all around the world will be using the CTBTO’s data in the next months and year to come, to better understand this phenomena and to learn more about the altitude, energy released and how the meteor broke up."
The CTBTO infrasound network is one of four systems used by CTBTO for detecting nuclear explosions since April 2001, when the first station came online in Germany. Infrared sounds are generated by all manner of natural and man-made sources including exploding volcanoes, earthquakes, meteors, storms and auroras, plus nuclear, mining and large chemical explosions, and aircraft and rocket launches.
The first recorded infrasound event was when Krakatoa exploded in 1883. The infrasonic sounds circled the Earth at least seven times and blew in windows hundreds of miles away. This ability of infrasound to travel globally has proven an excellent way of detecting nuclear explosions because of the distinct signature that such detonations produce.
The CTBTO detector stations are located in remote locations in order to minimize natural and man-made background noise. They work by recording minute changes in the atmospheric pressure using microbarometers.
The video below has an audible version of the infrasound detected.
Source: CTBTO via Popular Science
