What to do if you find a meteorite

Ever come across an unusual rock and wondered if it's a meteorite? Mark McIntyre explains how to tell if that stone really is a fragment from outer space

- Mark McIntyre

We're all fascinated by meteorites, ancient stony visitors from outer space. But what exactly are they, how do they get here and how can you tell if you've found one?

Most meteorites are fragments of material left over from the time when the Solar System was forming. Some never got scooped up by the gravity of a newly created planet, so they're orbiting the Sun alone. Others ended up as part of an asteroid or in the nucleus of a comet. Some meteorites come from other planets, dwarf planets or moons, including lunar and Martian fragments that were ejected into space following an impact.

So you can see why these objects capture our imaginations. They offer us a chance to study the conditions of the early Solar System or the surface of another planet without having to go there. Indeed, meteorites are still the only samples we have from Mars or some of the dwarf planets like Ceres, so they are an invaluable source of information.

How do these fragments end up on Earth? Over millions of years, the gravity of the planets, especially Jupiter, has pushed asteroids into particular orbits, such as the asteroid belt between Mars and Jupiter. Collisions between asteroids create large fragments, small particles and dust, some of which get nudged into new orbits that take them towards Earth, where they burn up in our atmosphere to form a meteor.

Comets that formed far beyond the orbit of Neptune can also be nudged into new orbits that bring them to the inner Solar System. As a comet nears the Sun, its icy nucleus starts to sublimate, releasing a trail of trapped dust. When Earth passes through this dust, these particles will also burn up in our atmosphere as meteors. Cometary debris is responsible for most of our meteor showers.

What are the chances?