Most meteorite were created by collisions between larger rocks. They either came from an asteroid or a planet. More than 99% came from asteroids. Evidence from isotopic and chemical signatures indicate that most came from about 100 original asteroids (though there may be many more that have never come to Earth). Almost all of these have been smashed to bits. Some asteroids appear to be reformed out of smashed up bits!

The original solar system condensed into dust particles and little balls called chondrules. These range from the microscopic to a centimetre or so. Chondrules and dust were drawn together by gravity and formed the planets and the asteroids. When asteroids got smashed up by collisions, they formed chondrite meteoroids. These make up about 87% of all meteorites found.

Some asteroids were so large that radioactive elements (mainly Aluminium 26) heated their cores and melted them. The heavier metals they contained (mainly iron and nickel) sank to their cores and the lighter stony material floated to the top – differentiating the asteroid. When these asteroids got smashed up by collisions, they formed three types of meteoroids. The cores formed iron meteoroids (4%), the core mantle boundary formed stony irons (1%) and the mantle and crust formed achondrite (without chondrules) meteoroids (8%).

A few achondrites originate from the crust of planets when they were hit by asteroids. Find out how we know

Finding Martians on Earth - analyse a meteorite found in Antarctica to find out if it is from an alien planet