WHAT THEY ARE

A meteorite is part of a planet, comet or asteroid which detached in an impact with another asteroid, comet or planet. It can also be a piece of space dust floating around. A brilliant meteor, called a fireball, may weigh many kilograms, but even a meteor weighing less than a gram can produce a beautiful trail. Some of these visitors from space are large enough to survive (at least partially) their trip through the atmosphere and impact the ground as meteorites. Fireballs are sometimes followed by trails of light that persist for up to 30 minutes; some, called bolides, explode with a loud thunderous sound. A meteor, sometimes called a "shooting star," can be the brightest object in the night sky, yet meteoroids are the smallest bodies in the solar system that can be observed by eye. Wandering through space, perhaps as debris left behind by a comet, meteoroids enter the earth's atmosphere, are heated by friction, and for a few seconds streak across the sky as a meteor with a glowing trail.
Collisions between the planet Mars and asteroids have blasted chunks of the planet into space. Occasionally, a piece of Mars will strike the Earth, as this meteorite did about 13,000 years ago. Astronomers believe that this meteorite, called ALH84001, was blasted off of Mars about 16 million years ago.