Where do meteorites come from?
Most meteorites are fragments of asteroids, chipped off in collisions in the asteroid belt between Mars and Jupiter. A small number come from the Moon and from Mars.
The asteroid belt holds millions of rocky and metallic bodies orbiting the Sun between Mars and Jupiter. Over billions of years they have collided again and again, scattering fragments of all sizes. Most of that debris stays in the belt, but some is gradually pushed into new orbits that cross Earth's path.
Two processes do the pushing. Jupiter's powerful gravity creates zones called resonances, where a fragment's orbit is repeatedly tugged until it becomes stretched and can reach the inner Solar System. Meanwhile, a gentle effect of sunlight called the Yarkovsky effect, in which a spinning rock absorbs heat and re-radiates it unevenly, slowly drifts small bodies towards those resonances. Once a fragment is on an Earth-crossing orbit, it may wander for millions of years before finally hitting our planet.
How do we know this? Camera networks that photograph bright fireballs can reconstruct a meteorite's orbit before it hit the atmosphere. Starting with the Příbram meteorite, which fell in what is now the Czech Republic in 1959, these orbits have traced back towards the asteroid belt again and again. Laboratory studies of grains brought back from asteroid Itokawa by Japan's Hayabusa mission also matched the most common kind of meteorite.
Not every meteorite is an asteroid fragment. Several hundred are pieces of the Moon, and several hundred more come from Mars, thrown into space when large impacts struck those worlds. Scientists recognise them through their chemistry and, for Martian meteorites, through gas trapped inside that matches the Martian atmosphere. Comets shed vast amounts of dust that produce meteor showers, but that material is generally too fragile to survive as a stone you could pick up.