VERIFICATION SCIENCE with Margaret Campbell-Brown INTERVIEW Associate Professor, The University of Western Ontario The Chelyabinsk meteor: Massive blast detected by 17 infrasound stations

The CTBTO's infrasound station IS18 in Qaanaaq, Greenland, one of the stations that detected the Chelyabinsk meteorite on 15 February 2013. Photo courtesy of Owen Kilgour.

»Statistically, something this size of the meteoroid, the Sudanese desert), but that is the its mass could be only time an object has been observed hits the Earth approximately calculated directly in space and subsequently collided once every 50 years (though from the energy. with the Earth. A detection just before There was tremendous impact was not possible for this object, nothing this size or larger has been interest in the size of because it approached the Earth from observed to hit the Earth since the object, but the the direction of the sun, and was video records are very obscured by the sun’s glare. 1908). This event was nearly ten difficult to calibrate, times as energetic as the Sulawesi, so infrasound was the How often would you expect an event of Indonesia fireball of 2009.« first publicly available, this magnitude to occur and how large accurate size estimate. was it in comparison with the bolide that exploded over Sulawesi, Indonesia, in Why did the meteor go October 2009, which was recorded by 15 On 15 February 2013 at 03:22 GMT, 17 of undetected until it hit the atmosphere? of the CTBTO’s infrasound stations? the CTBTO’s infrasound stations detected signals from an object that entered the Very few objects in this size range Statistically, something this size hits atmosphere and disintegrated in the skies are currently tracked. There are likely the Earth approximately once every over Chelyabinsk, Russia. The furthest hundreds of thousands of objects 50 years (though nothing this size or station to record the sub-audible sound this size in orbits which intersect the larger has been observed to hit the was 15,000km away in Antarctica. How Earth’s, but they are faint objects, and Earth since 1908). This event was did data from these infrasound stations currently operating surveys cannot nearly ten times as energetic as the allow scientists to refine their estimates track a meaningful number of them Sulawesi, Indonesia fireball of 2009. for the size of the meteor? (though some planned surveys may allow many of them to be discovered Just days earlier on 12 February 2013, A great advantage of infrasound and monitored). An object smaller the Democratic People’s Republic of is that data are quickly available than this one was observed for about Korea (DPRK) claimed that it had and energy estimates can be made a day before it struck the Earth in conducted a nuclear test. A total of 94 of relatively quickly. Given the speed 2008 (object TC3 2008, which fell in the CTBTO’s seismic sensors registered

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CTBTO SPECTRUM 20 | JUly 2013 A visual representation of the infrasound waves and parameters by the CTBTO’s International Data Centre, from the fireball recorded by the CTBTO station in Kazakhstan.

the event, which measured 4.9 in as contributing to climate change on the size of the impactor. With more magnitude. In addition, two infrasound research. What more do you think refined models of the atmospheric stations that are part of the network also scientists can learn about the Russian conditions at the time, the various detected signals. This was the first time meteor explosion on 15 February 2013 parts of the signal may be associated that the CTBTO’s infrasound stations had from CTBTO infrasound data? with fragmentation events and points registered a nuclear test. How large along the trail, giving a better idea of would you estimate the size of the The infrasound data provided what was happening to the object as it explosion over Chelyabinsk to have been excellent near-real-time information disintegrated in the atmosphere. in comparison with the nuclear test that the DPRK claims to have carried out?

I don’t know the energy of the 12 February event, but the meteor was Biographical notes certainly orders of magnitude more energetic. Margaret Campbell-Brown is an Associate Professor in the Since the Comprehensive Nuclear- Department of Physics and Test-Ban Treaty (CTBT) opened for Astronomy at the University of signature in 1996, infrasound Western Ontario, Canada. Her research focuses on small bodies in technology has experienced a the solar system, particularly renaissance. While the primary purpose meteoroids. Current research topics of CTBTO infrasound monitoring is to include the interaction of meteoroids monitor compliance with the CTBT, the with the Earth's atmosphere for large data also offer a range of potential civil and small impactors, characterizing the sporadic meteoroid environment, and scientific applications. In addition to and high resolution studies of providing information on meteors meteoroid ablation to determine the entering the atmosphere, the data could composition and structure of be used to monitor aurorae, chemical meteoroids. explosions, volcanic ash clouds as well

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CTBTO SPECTRUM 20 | July 2013