Meteorites, Asteroids and Comets

Asteroids, comets and meteorites are the small bodies and leftover debris of the solar system, distinct from the planets and their moons. Asteroids are rocky or metallic objects, most of which orbit the Sun in the asteroid belt between Mars and Jupiter, ranging from tiny fragments to bodies hundreds of kilometres across. Comets are icy bodies that, when they approach the Sun, release gas and dust to form a glowing coma and often a long tail pointing away from the Sun.

The related terms are easily confused. A meteoroid is a small rocky or metallic fragment travelling through space. When such a fragment enters Earth's atmosphere and burns up, the streak of light it produces is a meteor, sometimes called a shooting star. If any part survives the fall and reaches the ground, that surviving piece is a meteorite. Meteor showers occur when Earth passes through trails of debris left behind by comets, so the sky shows many meteors radiating from one direction.

Impacts from these bodies have repeatedly affected Earth and other worlds, leaving craters such as those preserved on the Moon and Mercury. The Tunguska event of 1908 flattened a large area of Siberian forest, and a major impact is widely linked to the mass extinction that ended the age of the dinosaurs. Studying meteorites, many of which are older than any rock on Earth's surface, gives scientists direct samples of the early solar system and clues to how the planets formed.

Frequently asked questions

What is the difference between a meteor and a meteorite?

A meteor is the flash of light produced as a fragment burns up in the atmosphere; a meteorite is the solid piece that survives and lands on the ground.

How do asteroids and comets differ?

Asteroids are mostly rock and metal and orbit closer to the Sun, while comets are icy and develop a glowing coma and tail when heated near the Sun.

What causes a meteor shower?

Earth passing through a stream of dust shed by a comet; the particles enter the atmosphere together and appear to radiate from one point in the sky.