Earth's atmosphere provides a safety buffer that protects us from (most) incoming space rocks.
In this image taken during the 2001 Leonid meteor shower, several bright fireballs are seen shining across the sky. Credit: Tony Hallas
As the Earth orbits the Sun, our planet regularly passes through the dust and debris left in our path by passing comets and asteroids. Each time this happens, the Earth experiences a meteor shower that fills the sky with brilliant rays of light. These “shooting stars” are the result of clouds of cosmic debris burning up in our atmosphere. But do the remains of a meteor shower ever reach the ground in the form of a meteorite?
The answer is NoMeteor showers, despite their impressive light shows, do not actually produce meteorites.
Meteorite vs meteorite
Space rocks are given different names depending on their environment. When a piece of dust or rocky debris floats through space, it is called meteoroid.
TO meteoriteOn the other hand, it is the brief ray of light seen in the sky when a space rock collides with our atmosphere, generating friction that creates heat and light.
Finally, a meteorite It is any part of a space rock that survives its dramatic fall to the ground.
Most meteorites occur high up Earth's atmosphereat altitudes of about 80 to 120 kilometers. This layer of the atmosphere is called the mesosphere. (For the purposes of spaceflight, the Kármán line defines where our atmosphere ends and space begins. It is located 100 kilometers above sea level. However, the upper layers of our atmosphere actually extend hundreds of kilometers above the ground.)
The faster a meteorite travels through the atmosphere, the sooner it will generate enough friction to ignite. That's why meteor showers made up of faster-moving particles (those orbiting in the opposite direction to the Earth's motion around the Sun) appear higher in the sky than slower-moving ones.
But even when Earth isn't flying through a giant cloud of debris and experiencing a meteor shower, the inner solar system is still peppered with random space dust and rocks. That means meteors can appear at any time. On any given night, the so-called sporadic background rate of meteors is about two to seven per hour. During meteor showers, that rate can increase — sometimes as much as tenfold or more.
Only the great survive
Whether or not a space rock survives its fall to Earth (which is rare) depends on factors such as its original size, speed, and angle of attack. Larger meteoroids that fall more directly through Earth's atmosphere are more likely to hit the ground as meteorites. This is because they have less distance to travel and more material to spare. Even if its outer layers burn off, some piece of its core is likely to survive, although it will be much smaller than when it began its fall.
How much smaller? According to the Institute of Planetary SciencesA meteoroid the size of a Volkswagen Beetle would eventually become a meteorite the size of a microwave oven as it passed through the atmosphere. And a space rock the size of a basketball could leave behind a meteorite the size of a softball. Of course, these sizes only apply to meteoroids made of dense, tough material. Fluffier or more delicate space rocks would end up being much smaller upon impact.
The clouds of cometary debris that Earth regularly passes through (like a child running through a stream of water) are made up of tiny grains of rock and dust, typically ranging in size from a grain of sand to a pea. In addition, meteor shower particles tend to be “fluffy,” meaning they are not very dense and burn up easily in Earth's atmosphere.
Most meteoroids, whether or not associated with a meteor shower, also impact our atmosphere at oblique angles, causing them to simply skim the upper layers with no chance of reaching the surface. But even if they do so at steeper angles, their tiny forms burn up completely along the way, leaving nothing that can touch the ground.
So while meteor showers do produce plenty of meteors, they don't result in meteorites. And while this may seem unfortunate, it's certainly good news for observers: they don't have to worry about It's raining space rocks When they come out to enjoy a beautiful light show.
This article was originally published online on December 11, 2020.
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