The terms meteor, meteoroid, and meteorite are often confused, but they refer to different phases of a single object’s journey through space and Earth’s atmosphere. The object’s location and the physical process it is undergoing determine which label is appropriate. Understanding this process requires tracking the small celestial body from its origin in the solar system to its final resting place.
Meteoroid: The Object in Space
A meteoroid is a small body of rock or metal orbiting the Sun. These objects are significantly smaller than asteroids, typically ranging from a grain of dust up to about one meter in diameter. Most meteoroids originate as fragments broken off from larger asteroids or as debris trails left behind by comets.
These objects travel at immense speeds, sometimes exceeding 40 kilometers per second near Earth’s orbit. The International Astronomical Union defines a meteoroid as an object larger than an atom but substantially smaller than an asteroid. Asteroids are generally considered to be bodies larger than one meter. The meteoroid exists in this state until its path intersects with the atmosphere of a planet, at which point its designation changes.
Meteor: The Flash of Light
The moment a meteoroid enters Earth’s atmosphere at high velocity, it transforms into a meteor. A meteor is not a physical object, but the visible streak of light caused by atmospheric entry. This familiar flash, commonly called a “shooting star,” is the result of intense atmospheric friction.
The friction generates extreme heat, causing the outer layers of the meteoroid to vaporize. The surrounding air becomes superheated and incandescent, creating the bright trail visible across the night sky. Most meteoroids are small enough that they completely burn up during this process, never reaching the planet’s surface.
A heightened occurrence of these visible events is known as a meteor shower, which happens when Earth passes through a stream of debris left by a comet. The particles in these trails are typically small, often no larger than a grain of sand, producing a brilliant display of light. The visual spectacle of the meteor ends when the object either disintegrates completely or slows down sufficiently in the lower atmosphere.
Meteorite: The Relic on Earth
A meteorite is the physical remnant of a meteoroid that successfully survives the fiery passage through the atmosphere and lands on the planet’s surface. Only a small fraction of the space rocks that become meteors are large or durable enough to endure the intense ablation and fragmentation. The intense heat of entry creates a distinctive feature on the meteorite’s exterior known as a fusion crust.
This crust is a thin, dark, glassy layer formed by the melting and rapid re-solidification of the surface material during the object’s rapid deceleration. Meteorites are broadly classified into three main types based on their composition: stony, iron, and stony-iron. Stony meteorites, which are the most common, are composed primarily of silicate minerals, while iron meteorites are dense alloys of iron and nickel.
Scientists highly value these relics because they represent pristine samples of the solar system’s earliest matter. Some stony types, known as chondrites, are over 4.5 billion years old. Studying the chemical and mineralogical makeup of a meteorite offers direct insight into the conditions and processes that shaped the planets.