Asteroids, comets and meteoroids — Astronomy, 11–13 years
Small objects in space are not all alike. Their materials and paths help us tell asteroids, comets, meteoroids, meteors and meteorites apart.
Different kinds of space rock
An asteroid is a rocky or metallic body travelling through space, usually larger than a grain of dust. A meteoroid is a smaller piece; when it streaks through an atmosphere it is a meteor, and if a piece reaches the ground it is a meteorite. A comet contains lots of ice and dust and can grow a glowing tail near the Sun.
Why make these distinctions?
People first used one word for many bright streaks and falling rocks, but that hid important differences. Scientists needed to describe what they saw, predict possible paths and compare the material left behind. The names tell us whether an object is still in space, burning in air, or sitting on Earth.
From a flash to a name
Imagine a 2-centimetre piece of rock moving towards Earth. First, in space, it is a meteoroid. Next, air makes it glow as it travels through the atmosphere: we call the streak a meteor. If a surviving piece lands in a field, that piece is a meteorite. The object’s name changes with its place.
The bright line is not a rock
A common mistake is to call the bright streak itself a meteorite. That seems sensible because we see the flash and may later find a stone. But the flash is the object heating and glowing in the atmosphere, so it is a meteor; only a surviving piece on the ground is a meteorite.
Clues from ancient space
Meteorites are pieces of space that can be collected and tested in laboratories. Their minerals preserve clues about the young Solar System, and some contain carbon compounds linked with the chemistry of life. Space agencies also track asteroids because a close approach can matter for Earth’s safety.
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