How Meteors Form and What They Are

Two Perseid meteors streak across the Milky Way during the 2012 meteor shower in Oklahoma.
John Davis/Stocktrek Images / Getty Images

Experienced stargazers are familiar with meteors. They can fall any time of the day or night, but these bright flashes of light are much easier to see in dim light or darkness. While they are often referred to as "falling" or "shooting" stars, these bits of fiery rock actually have nothing to do with stars.

Key Takeaways: Meteors

  • Meteors are flashes of light made when bits of space rock speed through our atmosphere and burst into flames.
  • Meteors may be created by comets and asteroids but are not themselves comets and asteroids.
  • A meteorite is a space rock that survives the trip through the atmosphere and lands on the surface of a planet.
  • Meteors can be detected by the sounds they give off as they pass through the atmosphere.

Defining Meteors

Technically, "meteors" are flashes of light that occur when a small bit of space debris called a speeds through Earth's atmosphere. Meteors may be only about the size of a grain of sand or a pea, although some are small pebbles. The largest can be giant boulders the size of mountains. Most, however, result from tiny bits of space rock that happen to stray across Earth during its orbit. 

incoming meteor
Looking at an incoming meteor descend through Earth's atmosphere, as seen from the International Space Station. NASA

How Do Meteors Form?

When meteors hurtle through the layer of air surrounding Earth, friction caused by the molecules of gas that make up our planet's atmosphere heats them up, and the meteor's surface begins warm up and glow. Eventually, the heat and high speed combine to vaporize the meteor usually high above Earth's surface. Larger chunks of debris break apart, showering many pieces down through the sky. Most of those vaporize, too. When that happens, observers can see different colors in the "flare" surrounding the meteor. The colors are due to the gases in the atmosphere being heated up along with the meteor, as well as from materials inside the debris itself. Some larger pieces create very large "flares" in the sky, and are often referred to as "bolides."

Meteorite Impacts

Larger meteors that survive the trip through the atmosphere and and land on the Earth's surface, or in bodies of water, are known as meteorites. Meteorites are often very dark, smooth rocks, usually containing iron or a combination of stone and iron.

Many pieces of space rock that make it to the ground and are found by meteorite hunters are fairly small and incapable of doing much damage. Only the larger meteoroids will create a crater when they land. Nor are they smoking hot—another common misconception.

Meteorite Hunters
Meteorite Hunters. NASA Johnson Space Center

The piece of space rock that made Meteor Crater in Arizona, was about 160 feet (50 meters) across. The Chelyabinsk impactor that landed in Russia in 2013 was about 66 feet (20 meters) long and caused shock waves that shattered windows across a wide distance. Today, these kinds of large impacts are relatively rare on Earth, but billions of years ago when the Earth was formed, our planet was bombarded by incoming space rocks of all sizes.

Chelyabinsk meteor as seen from a dash cam.
The fireball created as a superbolide flared over Chelyabinsk, Russia, on February 15, 2013. This was shot with a dashcam. Wikimedia Commons, CC-BY.

Meteor Impact and the Death of the Dinosaurs

One of the largest and most "recent" impact events occurred nearly 65,000 years ago when a piece of space rock about 6 to 9 miles (10 to 15 kilometers) across smashed into Earth's surface near where the Mexico's Yucatan Peninsula is today. The region is called Chicxulub (pronounced "Cheesh-uh-loob") and wasn't discovered until the 1970s. The impact, which may actually have been caused by multiple incoming rocks, had a drastic impact on Earth, including earthquakes, tidal waves, and sudden and extended climate change caused by debris suspended in the atmosphere. The Chicxulub impactor dug out a crater some 93 miles (150 km) in diameter and is widely associated with a huge extinction of life that likely included most dinosaur species. 

Fortunately, those kinds of meteoroid impacts are fairly rare on our planet. They still occur on other worlds in the solar system. From those events, planetary scientists get a good idea of how cratering works on solid rock and ice surfaces, as well as in the upper atmospheres of the gas- and ice-giant planets. 

Is an Asteroid a Meteor?

Though they can be sources of meteors, asteroids are not meteors. They are separate, small bodies in the solar system. Asteroids supply meteor material through collisions, which scatter bits of their rock throughout space. Comets can also generate meteors, by spreading trails of rock and dust as they orbit the Sun. When Earth's orbit intersects the orbits of comet trails or asteroid debris, those bits of space material can get swept up. That's when they start the fiery trip through our atmosphere, vaporizing as they go. If anything survives to reach the ground, that's when they become meteorites.  

asteroid vesta
Asteroid Vesta has supplied some meteorites that landed on Earth. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Meteor Showers

There are a number of chances for Earth to plow trails of debris left behind by asteroid breakups and cometary orbits. When Earth does encounter a track of space debris, the resulting meteor events are called "meteor showers." They can result in anywhere from a few tens of meteors in the sky per hour each night up to nearly a hundred. It all depends on how thick the trail is and how many meteoroids make the final trip through our atmosphere. 

chart4b_orionids.jpg
A sample of what a meteor shower provides in the night sky. The meteors of the Orionid Meteor shower appear to radiate from the direction of the constellation Orion. They are, in reality, bits of dust from a comet vaporizing in Earth's upper atmosphere. Carolyn Collins Petersen