WHERE DO METEORITES COME FROM?
All meteorites come from inside our solar system. Most of them are fragments of asteroids that broke apart long ago in the asteroid belt, located between Mars and Jupiter. Such fragments orbit the Sun for some time-often millions of years-before colliding with Earth.
Watch an animation of a meteor burning up on entry into the atmosphere. The fragment crashes to the surface, and meteorites are the surviving fragments. (Get RealPlayer.)
Meteorites can be huge: the biggest one ever found weighs around 60 tons, roughly twice as much as the Ahnighito meteorite. People have also found meteorites that are quite small, about the size of beach pebbles or even grains of sand.
ASTEROIDS
The vast majority of meteorites are fragments of shattered asteroids. Asteroids are rocky bodies found mostly in the asteroid belt, between Mars and Jupiter. Jupiter is the largest planet in our solar system, and its gravity is very strong. Asteroids, which are much smaller than planets, are sometimes pulled out of the asteroid belt by the force of Jupiter's gravity. Many of these asteroids then travel toward the inner solar system—where they can collide with Earth.
PLANETS
A small number of meteorites are pieces of rock from the surfaces of other planets. These fragments were likely blasted off planets when they were hit by a large asteroid or comet. People have found meteorites that are definitely from the planet Mars, some of which are on display in this hall. Some meteorites might be from Mercury, but researchers are still investigating this claim.
MOON
The most famous moon rocks are those collected by astronauts who walked on the Moon. But small pieces of the Moon also occasionally reach Earth as meteorites. Such "lunar meteorites" are identical in composition to the astronauts' moon rocks, although they come from different locations-possibly even from the far side of the Moon, which never faces Earth.
COMETS
Meteorites might also come from comets. Made of dust, rock and ices, comets are typically found in the outer reaches of our solar system, beyond the orbit of the planet Neptune. Scientists have identified several meteorites that might be fragments of the rocky cores of comets.
METEORS
Meteors are not meteorites. Like meteorites, meteors are objects that enter Earth's atmosphere from space. But meteors-which are typically pieces of comet dust no larger than a grain of rice-burn up before reaching the ground. As they vaporize, they leave behind the fiery trails sometimes called "shooting stars," even though meteors are not really stars. The term "meteorite" refers only to those bodies that survive the trip through the atmosphere and reach Earth's surface.
METEOR SHOWERS
Meteor showers are among the most spectacular phenomena in the night sky. Meteors were named "shooting stars" because people once mistakenly believed they were stars falling from the sky. Certain meteor showers occur at predictable times each year, when Earth travels through the remains of a comet that passed near our planet long ago while in its orbit around the Sun.
