What is a meteorite?
A meteorite is a natural piece of rock or metal from space that has survived the fiery trip through Earth's atmosphere and landed on the ground. Almost all come from asteroids, with a small number from the Moon and Mars.
Picture a lump of rock drifting between the planets for millions of years. If its path crosses Earth's, it plunges into the atmosphere at tremendous speed, glows brightly and loses much of its outer material. Whatever reaches the ground intact is a meteorite. The word refers only to the surviving object, so a meteorite is something you can actually pick up and hold.
Most meteorites are fragments of asteroids, the rocky and metallic bodies that orbit the Sun, mainly between Mars and Jupiter. Several hundred known meteorites were blasted off the Moon or Mars by large impacts. Scientists sort them into three broad families: stony meteorites, which look rather like Earth rocks; iron meteorites, made largely of iron-nickel metal; and stony-irons, a mixture of the two.
Meteorites arrive all the time, although most land in oceans or remote places and are never seen. Some are observed as they fall, such as the Winchcombe meteorite, which landed on a driveway in Gloucestershire in 2021. Others lie undisturbed for thousands of years before being found, especially in deserts and on the Antarctic ice, where dark stones stand out clearly.
Why do they matter so much? Many meteorites are older than any rock on Earth, having formed about 4.56 billion years ago as the planets were taking shape. They carry a record of the Sun's birth, the building of planets and even the delivery of water and carbon compounds to the young Earth. Each one is a free sample of another world, delivered to our doorstep.