Meteorite
A meteorite is a piece of rock or metal from space that survives its fiery passage through Earth's atmosphere and lands on the ground.
Definition
A meteorite is a rock from space that survived its fiery passage through Earth's air and landed on the ground, a rare survivor you can hold in your hand as a real piece of another world. The three main types are stony (most common), iron (mostly iron and nickel), and stony-iron; most are fragments of asteroids, but a few have been identified as rocks blasted off the Moon or Mars by impacts. In more detail they are classified as chondrites, primitive stony meteorites containing chondrules that never melted since the solar nebula; achondrites, from differentiated bodies; irons, from the cores of shattered planetesimals; and stony-irons. Radiometric dating of chondrites gives $4.567$ billion years, the accepted age of the solar system, and objects larger than a few meters are only partly slowed by the atmosphere and strike at hypervelocity, blasting craters far larger than themselves.
Example
In February 2013 a $20\ \text{m}$ object entered over Chelyabinsk, Russia, at about $19\ \text{km/s}$, released energy equivalent to roughly $500$ kilotons of TNT in an airburst about $30\ \text{km}$ up, broke windows across the city, and scattered thousands of small meteorites over the snow. The Hoba meteorite in Namibia, an iron mass of about $60$ tonnes, is the largest ever found, and Meteor Crater in Arizona, about $1.2\ \text{km}$ wide, was made about $50{,}000$ years ago by an iron meteorite roughly $50\ \text{m}$ across.
Key Insight
A freshly fallen meteorite is not glowing hot; only the outer skin melts and the interior stays as cold as space. That skin forms a dark glassy fusion crust, which along with a magnetic metallic interior helps tell meteorites from ordinary rocks. Meteorites are free samples of bodies no spacecraft has visited: iron meteorites let us hold a planetesimal core in our hands, and carbonaceous chondrites contain amino acids and water, the raw ingredients delivered to the early Earth.