The solar system contains numerous objects smaller than planets, moons, or asteroids. These pieces of natural space debris orbit the Sun. Though individually small, these celestial bodies represent some of the oldest material left over from the formation of our planetary neighborhood.
Defining the Celestial Traveler
A meteoroid is defined as a solid, natural object moving in interplanetary space. Its classification is determined by its size and location. The International Astronomical Union (IAU) defines a meteoroid as an object ranging from about 30 micrometers—the size of a dust grain—up to one meter in diameter. Anything larger than this threshold is categorized as an asteroid, while smaller particles are called micrometeoroids or space dust.
The composition of meteoroids is varied, falling into three categories: rocky, metallic, or a combination of both. Rocky meteoroids are made of silicate minerals, similar to the Earth’s crust, while metallic ones are composed mainly of iron and nickel. To be classified as a meteoroid, the object must be located in space before it encounters a planet’s atmosphere.
The Crucial Distinction Between Meteor and Meteorite
The terms used to describe this space rock change based on its location. The transition from a meteoroid to a meteor occurs when the object enters a planet’s atmosphere. Friction with the air causes the object to heat rapidly, vaporizing its outer layers and creating a bright streak of light.
This visible streak of light is the phenomenon called a meteor, commonly known as a “shooting star.” The object itself remains a meteoroid, but the luminous trail it creates gives it a new name. Most meteors are caused by objects the size of a grain of sand or a small pebble, which burn up completely high above the Earth’s surface.
If the meteoroid is large enough to survive the passage through the atmosphere and reach the ground, the remaining fragment is classified as a meteorite. This means the extraterrestrial material has successfully landed on Earth. Meteorites are classified by their internal structure and composition, often grouped as stony, iron, or stony-iron types.
Where Meteoroids Originate
Meteoroids are fragments broken off from larger parent bodies within the solar system. They originate either from the asteroid belt or from comets. Collisions between asteroids in the main belt, located between Mars and Jupiter, regularly chip off pieces of rock and metal that become meteoroids.
Comets also shed material when they pass near the Sun, causing icy surfaces to vaporize and release embedded dust and rock particles. These fragments are often the source of meteor showers, as Earth passes through the debris trail left by a comet’s orbit. Some meteoroids have been ejected from the surfaces of the Moon and Mars following powerful impacts.