# Wikijunior:Solar System/Asteroid belt

!Asteroid belt between Mars &
Jupiter.PNG

The asteroid belt lies between the planets Mars and Jupiter. It contains
lumps of rock and metal much smaller than planets. These lumps are
called asteroids or minor planets. They are not visible from Earth with
the naked eye, but many may be seen through binoculars or small
telescopes.

+------------+----------+
| Object\    | Maximum\ |
| Name       | Size     |
+============+==========+
| 1 Ceres    | 933 km   |
+------------+----------+
| 4 Vesta    | 530 km   |
+------------+----------+
| 2 Pallas   | 525 km   |
+------------+----------+
| 10 Hygiea  | 407 km   |
+------------+----------+
| 511 Davida | 326 km   |
+------------+----------+

: Largest bodies in the asteroid belt

The largest asteroid in the solar system is called \"2001 KX76.\" In the
asteroid belt, the four largest bodies are Ceres (a dwarf planet named
after the Roman goddess of agriculture), Vesta (the Roman goddess of the
home), Pallas (the granddaughter of Poseidon), and Hygiea (the Greek
goddess of health). These four bodies make up about half of the asteroid
belt.

Some asteroids are less than a kilometer across. Unofficially the limit
has been set at 50 meters, and anything smaller than that is going to be
simply called a meteoroid. With advances in telescopes and particularly
for objects that travel close to the Earth, some objects smaller than 50
metres have indeed been seen passing nearby the Earth.

There are probably several million asteroids in the solar system. Over
96,000 asteroids have been given numbers. Almost 12,000 of them have
names. But even though there are a lot of asteroids, the asteroid belt
is mostly empty space. Traveling through the asteroid belt in a space
ship would not be very much like what you see in a science fiction film.
This would not be the same in the first 100 million years of the solar
system\'s history (had humans evolved and discovered film). The asteroid
belt lost 99.99% of its mass in the first 100 million years of the solar
system.

{{  }}

## What are they named after?

The first asteroids were named after mythical heroes and gods much like
the major planets. The first to be discovered was named Ceres after the
Roman goddess of growing plants (particularly grain) and of motherly
love. The second asteroid discovered was called Pallas and was named
after one of the Greek gods of wisdom. Asteroids are also given a number
in the order of their discovery, so Ceres is 1, Pallas is 2, and so
forth.

As the number of known asteroids increased, they ran out of mythical
names so other names were used instead. Some asteroids were named after
countries. For example asteroid number 136 is named Austria. Others were
named after plants, for example 978 Petunia. 1620 Geographos was named
after the National Geographic Society, in recognition to their efforts
at sharing knowledge about the Solar System. Many are named after
people, both alive and dead. In a couple of cases, like 2309 Mr. Spock,
asteroids were named after the discoverer\'s pet cat. This last type of
naming is discouraged, but it still happens from time to time. Even
fictional characters have been used.

Today, names for asteroids can be suggested by the people who discover
them. The names become official after a group of people reviews them to
make sure they are not offensive or too much like another name. Because
so many asteroids are now being found, most new asteroid discoveries are
not even getting a name at all, but rather a numbered code. It is not
likely that they will ever be given a formal name, at least in this
century.

The actual word *Asteroid* can refer to any member of the family of
Asteroidea; in other words, a starfish. The etymology of the word comes
from Ancient Greek *ἀστεροειδής*, literally meaning star form. The
Ancient Greeks probably must have mistook the asteroids for stars.

Most of the asteroids have symbols representing them; for example, Ceres
has ⚳, representing Ceres\'s scythe, and Pallas has ⚴, reperesenting
Athena\'s spear.

## Who discovered them?

```{=html}
<div style="float:right;  border:2px solid #aaaaaa; width:250px; margin-left:0.2em; padding:0.4em">
```
**Asteroid Belt Facts**:

-   The total mass of all the asteroids in the asteroid belt is about
    1/35th of that of our moon.
-   The largest object in the asteroid belt, Ceres, makes about 1/3 of
    the total weight of all the asteroids.
-   Ceres is the only dwarf planet in the asteroid belt.
-   Vesta is the only asteroid that can ever be seen with the naked eye.
    Its magnitude can reach +5.1, about the same as Uranus.
    -   Although people probably saw Vesta and Uranus thousands of years
        ago, they were not recognised to orbit the Sun until 200 years
        ago.

```{=html}
</div>
```
The first asteroid to be discovered was Ceres, on 1 January 1801, by
Giuseppe Piazzi accidentally. At first he thought this was a comet, then
later a planet! When it was realised it was too small Sir William
Herschel (the astronomer who discovered Uranus) made up the word
\"asteroid\" to describe it, using the Ancient Greek word *aster*,
meaning star, and the *-oid*, meaning form or shape. In other words a
star-like planet, because he couldn\'t see any details due to the small
size of the object.

By 1807 another 3 asteroids were discovered, but no more were found
until 1845 when a persistent asteroid hunter named Karl Ludwig Hencke
found a fifth, and sixth asteroid in 1847. Ever since then at least one
new asteroid has been found each year.

In 1891, the first pictures of the night sky were taken to find more
asteroids. This led to the discovery of many more asteroids. A picture
of the same part of the sky is taken on two different nights. When the
two pictures are lined up, the stars will be in the same places but an
asteroid will have moved.

In our modern times, over 280,000 asteroids have been discovered. Many
more are being found all the time. Some of these asteroids pass near the
earth and astronomers want to find any that come close to our planet.
Large numbers of asteroids are now being discovered by machines.

## What are they made of?

Three out of four asteroids are made of rock that is rich in carbon. The
rest are made of the metals iron and nickel. About half of these are
pure iron and nickel; the rest are mixed with compounds of silica, the
element that makes up rocks. Each of the larger metal asteroids contains
huge amounts of iron: much more than is mined every year on Earth.
Vesta, the brightest asteroid, has a very unusual composition - being
made of high-density volcanic rocks.

Scientists are very interested in what asteroids are made of because it
can help them learn how the solar system was formed. Several spacecraft
have visited asteroids to learn more about them.

## Are there asteroids outside of the asteroid belt?

framed\|right\|All the major asteroid clusters in the solar system. It
does look like the asteroid belt is clustered in the picture, but one
millimetre of emptiness in the picture means millions of kilometres
emptiness.Most asteroids are
found in the asteroid belt, but not all. Some asteroids orbit closer to
the Sun, and many asteroids orbit beyond Neptune. Asteroids that closely
approach Earth are called Near-Earth Asteroids. Sometimes pieces of
asteroids strike the Earth, burning in the atmosphere as a meteor. If
they are large enough, they might actually hit the surface and become
meteorites.

!Asteroid Ida and its
moon

A centaur is a mythical beast having a horse\'s body with a man\'s head
and torso in place of the head and neck of the horse. There are some
asteroids in the outer solar system that are called Centaurs. It is hard
to tell whether any one Centaur is an asteroid, comet, or Kuiper Belt
object. For example, the first Centaur to be discovered was Chiron(In
Greek Mythology, an important centaur). But some scientists think it is
a comet, not an asteroid. Officially it is called both the asteroid 2060
Chiron and the comet 95P/Chiron!

In most cases when an asteroid\'s orbit crosses the path of a planet
such as Jupiter, at some point the asteroid will either hit the planet
or else be hurled into another orbit. Many of the small moons of some
planets may have once been asteroids that were captured by the planet\'s
gravity when they came too close. However there are two points along the
orbit of a planet were an asteroid can safely linger. These are found at
a point one-sixth (or 60°) of an orbit ahead of the planet, and the same
distance behind the planet. These sites are called Lagrange points, and
they are found where the force of gravity from the Sun and the planet
balance out with the motion of the asteroid\'s orbit. The asteroids
found in these spots are called Trojans, and they move around the Sun at
the same velocity as the planet.

## Ceres

!The dwarf planet
Ceres._(cropped).jpg "The dwarf planet Ceres."){width="150"}

Ceres is a large Dwarf Planet like Pluto located in the asteroid field.
The difference between Ceres and most other dwarf planets is that it is
also an asteroid. Ceres is one of the few asteroids that are shaped like
a sphere, and it may have some ice just underneath its dusty surface. It
was discovered in 1801 by Giuseppe Piazzi, who was an Italian
astronomer.

## Some famous asteroids

Ceres the first discovered and biggest asteroid in the solar system.

The asteroid Ida has its own moon named Dactyl. A number of asteroid
moons have now been found.

Next Topic: Jupiter

## References

-   U.S. Naval Observatory Ephemerides of the Largest
    Asteroids,
    USNO.
-   Near Earth Asteroid Tracking, NASA.
-   Asteroids: Structure and composition of
    asteroids, ESA.
-   Main Asteroid Belt,
    SolStation.

pojas
de:Wikijunior Sonnensystem/
Asteroidengürtel
es:Wikichicos/Sistema_Solar/Cinturón_de_asteroides
nl:Wikijunior:Zonnestelsel/Planetoïdengordel
pl:Wikijunior:Układ_Słoneczny/Pas_planetoid
fi:Wikijunior_Aurinkokunta/Asteroidivyöhyke
zh:Wikijunior:太阳系/小行星带
