At intervals, however, hundreds of such meteors occur simultaneously and appear to emanate from a fixed point. These swarms are called meteor showers and are named after the constellation in which they seem to have their point of origin. Meteorite Meteor that reaches the surface of the earth or of another planet before it is entirely consumed. Although most meteorites are now believed to be fragments of either asteroids or comets, recent geochemical studies have shown that a few Antarctic stones came from the moon and Mars, from which they presumably were ejected by the explosive impact of asteroids. Asteroids themselves are fragments of planetesimals, formed some 4.6 billion years ago, while the earth was forming.
Meteorites generally have a pitted surface and fused charred crust.
The larger ones strike the earth with tremendous impact, creating huge craters. The largest known meteorite, estimated to weigh about 60 metric tons, is situated at Hoba West near Grootfontein, Namibia. Composed chiefly of iron, the three masses had long been used by the Inuit as a source of metal for the manufacture of knives and other weapons. The Ahnighito was brought to the United States by Peary and is on display at the Hayden Planetarium in New York City. The force of collision would have spewed molten rock far around the impact site.