What are asteroids?
An asteroid is a large rock in outer space.
Some, like Ceres, can be very large, while others
are as small as a grain of sand. Due to their
smaller size, asteroids do not have enough gravity
to pull themselves into the shape of a ball.
Astronomers group asteroids into different
categories based on the way they reflect
The asteroid belt is divided into an inner belt
and an outer belt. The inner belt, which is made
up of asteroids that are within 250 million miles
(402 million km) of the Sun, contains asteroids
that are made of metals.
The outer belt, which includes asteroids 250
million miles (402 million km) beyond the Sun,
consists of rocky asteroids. These asteroids
Asteroids are left over materials from the formation
of the Solar System. These materials were never
incorporated into a planet because of their
proximity to Jupiter's strong gravity.
How many asteroids are
26 very large asteroids have been discovered, which
is probably most of the big ones. But there are still
millions of smaller ones that we have yet to see
because they are too tiny, only a mile or so across.
If we stuck all the asteroids together, how big would
the new planet be?
If all the materials of all the asteroids were squashed
up into one planet it would be smaller than our moon.
While most asteroids can be found in the
Asteroid Belt, others are in strange orbits
straying far from home. It is currently
believed that at least 5000 asteroids cross
the Earth's orbit, some coming very close.
Don't worry though, asteroids and comets
only hit the Earth every 100 million years or
What are comets?
A comet is a small world which scientists
sometimes call a planetesimal. They are made out
of dust and ice, kind of like a dirty snow ball.
Where do they come
Comets come from two places: The Kuiper Belt
and the Oort Cloud.
Imagine a place far, far away at the very edge of
the Solar System. A place where millions of
comets can be seen swishing around in every
direction. These icy comets are orbiting the Sun
in two different places, both of which are very
distant. One place is called the Oort cloud, and
the other is called the Kuiper Belt.
Many people think that a comet's tail is always
following behind it, but actually the coma, or tail, can
either be behind the comet or in front of it. Which way
the tail is pointing depends on where the Sun . That's
right, the Sun's heat and radiation produce a wind
called the Solar Wind , as a comet gets close to the
Sun it begins to melt. The gas and dust that melt off
are blown away from the Sun by the solar winds. So if
a comet is traveling towards the Sun then the tail will
follow behind, but if the comet is traveling away from
the Sun the tail will be in front of the comet.
What meteorites are and
where they come from?
Meteorites are chunks of rocks or metal that fall
from space. They are named after the place they are
found. Most meteorites are very small but they can
be huge and weigh more than a car.
Where in space are they
Most meteorites come from the asteroid belt. This
is a region between Mars and Jupiter that contains
many rock fragments broken off from asteroids.
There are 31,000 meteorites that we know about
and all but 139 came from here.
A small number of meteorites are made from particles
from other planets. They are known as non-asteroid
Some of these come from Mars. Scientists know this
because small fragments of glass in these meteorites
contain particles of atmosphere from the planet it came
from. Martian meteorites are not as old as those from
the asteroid belt.
A small number of non-asteroid meteorites come from
the moon. They were broken off when asteroids and
comets hit the surface.
Some people claim they have been hit by meteorites
as they fall from the sky. This is extremely rare and
many cases are unproven.
The first human we know to be hit by a meteorite is
Ann Hodges who lived in Alabama, USA. In 1954,
a meteorite crashed through her ceiling and struck
her after bouncing off her radio. She was badly
bruised and had a lucky escape as the meteorite
weighed 4kg, about the same as a domestic cat.
The oldest report is from 1911 in Egypt when a dog
was said to have been killed by a Martian meteorite.
The Barwell meteorite was the biggest to fall over
Britain. It broke up and fell as a shower of stones
over the Leicestershire village of Barwell on
Christmas eve, 1965.
to fall on Britain.
What is the difference between an asteroid,
comet, meteoroid, meteor and meteorite?
A relatively small, inactive body,
composed of rock, carbon or metal,
which is orbiting the Sun.
relatively small, sometimes active
object, which is composed of dirt and
ices. Comets are characterized by
dust and gas tails when in proximity to
the Sun. Far from the Sun it is
difficult to distinguish an asteroid
from a comet.
A small particle from an asteroid or
comet orbiting he Sun.
burns up in the Earth's atmosphere -
A meteoroid that is observed as it
a shooting star.
meteoroid that survives its passage
A particular slide catching your eye?
Clipping is a handy way to collect important slides you want to go back to later.