Monitoring stations normally used to keep tabs on the nuclear tests of regimes like North Korea's captured the arrival of a rock from outer space.
On the morning of February 15, a rock from outer space blazed above Chelyabinsk, Russia, for a few seconds and then it was gone -- just fragments and dust scattered across the Earth below.
For scientists trying to piece together the story of this meteor that no one saw coming, they need evidence. But what is there? The moment is gone; all that's left are the meteorite fragments and any recordings that happened to be rolling the moment the meteor arrived. And scientists lucked out: The prevalence of dashboard cams in Russia has provided a rich set of data. But that's not all -- another of humanity's constantly rolling transcription devices captured the event loud and clear: 17 infrasound-recording stations around the globe heard the boom.
The stations are part of the global monitoring network of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), which keeps the Treaty's member states apprised of any possible nuclear explosions around the world. Just days before the Russian Meteor, the CTBTO had detected such a blast: North Korea's February 12 nuclear test.
Around the world, the CTBTO has 45 monitoring stations that are constantly listening for sound waves far too low for the human ear to hear. Such infrasounds, as they are known, can travel much farther than the frequencies we are used to, sometimes wrapping around the entire planet several times, as was the case with the Krakatoa volcanic eruption in 1883, the Tunguska meteorite in 1908, and nuclear tests in the middle of the 20th century.
A video from the CTBTO shows what these stations are like (this one in Qaanaaq, Greenland):
Normally, these stations are there waiting for signs of a nuclear explosion. But on February 15, sites as far away from the Ural Mountains as Antarctica (15,000 km away) and Alaska (6,500 km away) detected infrasounds resulting from the Russian meteor.
Here, for example, is what CTBTO's Kazakh sound station heard, sped up *135 times* -- making it is audible to the human ear.
Based on the sounds the CTBTO recorded, scientists are able to study the meteor's direction, energy release, and duration. "We know it's not a fixed explosion because we can see the change in direction as the meteorite moves towards the earth. 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," said acoustic scientist Pierrick Mialle in a statement.
The data revealed that the asteroid was 17 meters in diameter, weighed 10,000 metric tons, struck the atmosphere at 40,000 miles per hour (damn!), and exploded into piece 12 to 15 miles above ground, according a video report from NASA.
Watch the video in its entirety for more (but beware of NASA's comparison of the meteor to a nuclear explosion):