Large meteor fireballs can cause a loud boom noise, like thunder, and all good meteorite hunters know… this likely means there are rocks on the ground. But why? Read this article to learn more about these boom and also other sounds produced by meteors, and also how experts can use sounds to help locate meteorites.
A meteorite slammed into the ground in South Texas last night, and you can hear the boom and see birds fly from this home camera…A newscaster reporting on the 2023 San Isidro Texas Meteor Event, incorrectly identifying the sonic boom as the sound of a meteorite hitting the ground.
In the video, a newcaster makes a common mistake, identifying the sound of a sonic boom as the sound of a meteorite hitting the ground. Sonic booms are actually generated in the air when meteor fireballs occur, because the meteoroid is travelling at hypersonics speeds (faster than the speed of sound). If a sonic boom is heard by people on the ground, it means that large meteorites were associated with that meteor fireball.
Meteors Produce Three Types of Sounds
In addition to sonic booms, two other lesser known sounds are associated with meteor fireballs. Read this summary of the three types of sounds generated by meteors:
- Sonic Boom – the accumulation of sound waves emitted from any object travelling at greater than the speed of sound (~343 m/s), which arrive to the observer as a loud “boom”. Meteoroids enter the atmosphere at speeds ranging from 10 to 50 km/s and often maintain supersonic flight to an altitude of less than 20 kilometers above the ground. The sonic boom produced at these lower altitudes often reach the ground, and people within the immediate area of the fireball report hearing a loud boom or booms, or a sound like rolling thunder, a few minutes after a fireball is witnessed.
- Terminal Sounds – The arrival of meteorite fragments, (travelling at subsonic speeds) is often accompanied by a unique sound, which is described by witnesses, in the few seconds before they hit the ground. This sound occurs after the boom and can only be heard within a short distance of where the meteorites land (typically within 100 meters). Sometimes the thud of the meteorite impacting the ground is also heard at the end of the terminal sound. We have compiled here a colorful list of descriptions of terminal sounds, from Frank Cressy’s book, “From Weston To Creston, A Compendium of Witnessed US Meteorite Falls 1807 to 2016”:
- “hissing sound, compared to that of a of an engine blowing off steam” – 32kg mass, Allegan, Michigan, USA (1899)
- “loud noise resembling that of a buzz saw” – 3.2kg mass, Andover, Maine, USA (1898)
- “peculiar humming or singing noise, like an airplane flying high. … It changed to a whizzing noise and ended in a swish and a thud.” – 265g mass Athens, Alabama, USA (1933)
- “whizzing like a steam-saw going through a plank” – 5.9kg mass, Bath Furnace, Kentucky, USA (1902)
- “strange whistling sound” – 960g mass, Berthoud, Colorado, USA (2004)
- “the chopping sound made by a helicopter, but changing pitch as it approached” – 1.5kg mass, Burnwell, Kentucky, USA (1990)
- “whistling noise reminding him of an incoming mortar round” – 1.4kg mass, Claxton, Georgia, USA (1984)
- “whisting of bullets” – 200g mass, Deal, New Jersey, USA (1829)
- “there were shattering fragments, with a loud sound, prrrr! …it fell from the sky and we were over there, the sound was just on this side only and it was continuous like a passing airplane woooo” – Kombuini, Kenya (2020)
- Photoacoustic sounds – Another type of sound is sometimes described by witnesses, as a popping, swishing, or sizzling sound, concurrent with the observation of the meteor (at the same time as the visible meteor). The effect is not fully understood, but scientists have theorized that the sound comes from high frequency light pulsations, which induce vibrations in the environment surrounding the observer (Spurny, 2015).
Sonic Boom Animation
Using Sonic Booms to Locate Meteorites
Notes from Pat Branch:
A sonic boom is a traveling wave, but it is not really that long, compared to the whole path of the meteor… and it is not associated with fragmentation at all. A sonic boom will typically occur during the last 10 km or so on the flight path. The meteor has to be low enough to have some atmosphere to carry the sonic boom to the ground, so it only happens when a meteor has gotten below 50 km or so.
Rocks break apart but they do not separate very far… so the rumble represents a very short distance in the path. A stone has to be big enough to produce a wave that can make it to the ground. A 50 gram stone will not do it. If you have two 200 gram stones traveling at supersonic speeds and you hear a 1 sec long rumble those rocks are about 305 meters apart. The boom is not a single point, but instead it is a path in the air (say 10 km long) that spreads to the sides as it goes to the ground, producing an arc-shaped cone on the ground with varying pressure differences, based on where it was produced and the size of the rock. A 1 Pascal pressure wave is a big window rattler. We usually only get 0.1 Pascal or so for a “typical” fireball.
This path on the ground can be huge, of course, and heard tens of kilometers from the path and register on seismic stations hundreds of kilometers away. I usually give the boom a smaller circle shape on my plots. If it does not triangulate well, it isually means a high boom and a burn-out. Meteorite-droppers tend to triangulate well. There can be holes in the sonic boom arc (or footprint on the ground), as sometimes the pressure waves cancel each other out. So, someone right under the path can often not hear it where someone farther away can hear it.
A sonic boom is a good indication of a meteorite-dropping event, because rocks have to be large and low to create a boom that is audible on the ground.Pat Branch, Sonic Data Analysis Expert for Strewnify
Explosions in the visible event really have nothing to do with the sonic boom on the ground. A sonic boom is a good indication of a meteorite-dropping event, because rocks have to be large and low to create a boom that is audible on the ground. Cometary-type material can still burn up before reaching the ground. A fragmentation event can break a rock into small enough pieces that they burn up before reaching the ground also. The end point of the sonic boom tends to be the point where dark flight begins. I usually give it 4-8 km past the sonic boom triangulation.
The author and founder of Strewnify.com, an automotive controls engineer, with a passion for physics.
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