what is a metearoid?

A small body moving in the solar system that would become a meteor if it entered the earth's atmosphere.

Most of us probably have seen meteors or shooting stars. A meteor is the flash of light that we see in the night sky when a small chunk of interplanetary debris burns up as it passes through our atmosphere. "Meteor" refers to the flash of light caused by the debris, not the debris itself.

The debris is called a meteoroid. A meteoroid is a piece of interplanetary matter that is smaller than a kilometer and frequently only millimeters in size. Most meteoroids that enter the Earth's atmosphere are so small that they vaporize completely and never reach the planet's surface.

If any part of a meteoroid survives the fall through the atmosphere and lands on Earth, it is called a meteorite. Although the vast majority of meteorites are very small, their size can range from about a fraction of a gram (the size of a pebble) to 100 kilograms (220 lbs) or more (the size of a huge, life-destroying boulder).

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Meteorites are fragments of rock and/or metal thatfall to Earthfrom space. Having broken away from a larger extraterrestrial body, meteorites can measure anything from a fraction of a millimetre to the size of a football pitch and bigger.

Captured by Earth's gravitational force, they are accelerated to speeds of over 11.2 kilometres per second. As they enter Earth's thick atmosphere they slow rapidly due to the friction andglow, flashing across the sky like a firework, before finally crashing to the ground.

Where do meteorites come from?

Most meteorites are fragments that have come away as 2 asteroids collide. Asteroids are irregular-shaped rocks that orbit the Sun. There are thousands of asteroids in our solar system, most in an orbit between Mars and Jupiter known as the asteroid belt. The asteroid belt was formed when the solar system was born about 4,568 million years ago, from a cloud of gas, dust and ice.

A small proportion of meteorites come from the Moon and the planet Mars. These meteorites are much younger than those from asteroids, some as young as 2,500-million-years-old and 180-million-years-old respectively. We know where they have come from because their composition is very similar to Moon rock brought back from the Apollo lunar mission and Martian soil from the Viking probe.

Where are meteorites found?

Although not many meteorites are seen hitting the ground and most fall into the sea, thousands are found each year. Meteorites can be found all over the world, but are easiest to spot in dry places, such asdeserts, where they do not erode quickly and are less likely to be hidden by vegetation.

Scientists known ascosmochemistsare able to work out what has happened throughout the life of a meteorite by studying its chemical structure, revealing a little piece of the solar system's history one rocky chunk at a time.