Travelers in space
Not all matter in the solar system has been brought together
to form the Sun and the planets. Clumps of rock and ice travel through
space, often in highly elliptical orbits that carry them towards the Sun
from the far reaches of the Solar System. Comets are icy planetary bodies
that take their name from the Greek description of them as aster kometes,
or "long haired stars". Asteroids are bits of rock that have never managed
to come together as planets. Scientist are not sure why, but they think
that Jupiter's powerful gravity flung the nearby debris into various eccentric
orbits, causing some of the larger asteroids to crash together and break
up. A meteor is a piece of space rock - usually a small piece of a comet
- that enters the Earth's atmosphere. As it falls, it begins to burn up
and produces spectacular fireworks. A meteor that survives long enough
to hit the Earth - usually a stray fragment from the asteroid belt - is
called a meteorite.
