Meteorites

Meteorites are solid fragments originating from astronomical bodies that survive their passage through space and strike a planet’s surface. During entry into Earth's atmosphere they are briefly luminous as meteors or shooting stars; once they reach the ground, the recovered rock is called a meteorite. Meteorites provide physical samples of bodies from the solar system, and they can range from tiny grains to large boulders.

Most meteorites come from the asteroid belt between Mars and Jupiter, generated by collisions that eject fragments into Earth-crossing orbits. They are broadly divided into three principal classes: irons, stones, and stony-iron meteorites. Iron meteorites consist mainly of iron-nickel metal and are often fragments of the cores of differentiated parent bodies. Stone meteorites are largely silicate rocks and include chondrites, which preserve chondrules and are among the oldest materials in the solar system, and achondrites, which show signs of melting. Stony- irons contain both metal and silicate material. In addition, a small number originate from the Moon or Mars; these lunar and Martian meteorites were ejected by impacts and later delivered to Earth.

Meteorites are studied by meteoriticists who use petrographic examination, chemical and isotopic analyses, and radiometric dating to determine their age, origin, and thermal history. They inform models of solar system formation, planetary differentiation, and the early bombardment history of the inner planets. Collecting involves classifying items as falls or finds; falls are witnessed drops, while finds are discovered without a witnessed meteor. Meteorites are catalogued by size, mineralogy, and isotopic composition, and many are valued as scientific and educational resources.