Asteroids, comets and meteoroids

Asteroids, comets and meteoroids are relatively minor but particularly important components of the Solar System. In recent years, much concern has been raised at the prospect of a collision between the Earth and any one of these objects and the environmental impact that such a collision might have.


Asteroids are relatively small rocky objects that orbit the Sun. Most asteroids occupy a region of space known as the asteroid belt between Mars and Jupiter. Belt asteroids can be irregular or spherical in shape and vary considerably in size. Some of the larger belt asteroids have been identified and named. The largest known is Ceres (about 900km across). Belt asteroids can have satellite asteroids of their own. Some asteroids are co- orbital with Jupiter while others have irregular orbits that cut across the path of the Earth. Asteroids may represent the debris of failed planets or moons. Their origin remains uncertain.



Comets are essentially chunks of ice and rock, dirty snowballs if you like, that formed during the early history of the Solar System and generally occupy a region of space known as the Oort cloud between 10,000 and 100,000AU from the Sun. Some comets follow highly elliptical paths that bring them very close to the Sun. As a comet approaches the Sun its icy nucleus begins to vaporize producing a large head (or coma) with a long tail pushed away from the Sun by the solar wind. A comets tail can stretch through space for millions of kilometres. Many comets are regular and frequent visitors to the inner reaches of the Solar System, others are thought to return over a time scale measured in millions of years.


Meteoroids Most meteoroids are particles of dust and rock derived from comets as they orbit the Sun. If a meteoroid should enter the Earth’s atmosphere it produces a meteor (or trail) commonly referred to as a ‘shooting star’. Spectacular meteor showers are produced when the Earth passes through bands of cometary debris. Meteoroid fragments which survive passing through the Earths atmosphere and make it to the Earths surface are known as meteorites.

Exploring the Earth-Sun-Moon System


The Universe
The Milky Way Galaxy
Constellations, Surveying the Solar System
The Sun
Planets and their moons
Day and night
Seasonal change
The Moon's phases and eclipses
Further Reading
Self assessment(1)
Self assessment(2)
Self assessment(3)