Dutch scientists have detected ultra-low frequency sound waves - infrasound - from a meteor that exploded over Germany in November 1999.
The force of the explosion would have been equivalent to 1.5 kilotons of TNT, about the same as a small nuclear weapon.
The signals were detected by the seismology division of the Royal Netherlands Meteorological Institute. Its researchers operate an infrasound observatory, which consists of an array of micro-barometers that can detect very low-frequency (0.002 to 40 hertz) sound.
The world is full of sounds that humans cannot hear. Infrasound is too low for us but if we could hear it we would be deafened with the noise produced by thunderstorms, ocean waves, creaking continents and meteors.
Writing in the Geophysical Research Letters, the researchers describe an event they detected on 8 November, 1999. An intense burst of infrasound came from the northeast. It was later identified as a meteor explosion in the atmosphere over northern Germany. Several people provided eyewitness accounts of the flash in the sky.
From all the available data, it seems that the meteor exploded at an altitude of about 15 km (9 miles).
Some astronomers are taking a keen interest in infrasound. They hope it could provide valuable data for estimating the number of unseen meteor explosions in our atmosphere.
Infrasound can also be used to detect the explosions from nuclear weapons. A global network of about 60 infrasound facilities keeps an "ear" on signatories to the Comprehensive Test Ban Treaty to see that they are meeting their obligations.