# Wikijunior:Solar System/Kuiper Belt

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**Kuiper Belt Facts**:

-   The Kuiper belt is the most recently discovered section of the Solar
    System.

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Beyond the **orbit** of Neptune lies the Kuiper belt. It extends outward
an additional three billion kilometers away from the Sun. The belt
contains different-sized lumps of icy mixtures. These lumps are called
Kuiper belt objects. The biggest are called minor planets or dwarf
planets. The Kuiper belt may have formed when the gravity of the young
planet Jupiter hurled the objects out to where they are now. The Kuiper
belt is named after Gerard Kuiper (rhymes with \"viper\"), one of
several astronomers who hypothesized about a field of small objects
beyond Neptune.

### What are Kuiper belt objects?

The objects in the Kuiper belt are frozen mixtures of dirt, ice and
**organic compounds**. They are a lot like **comets**. Some of the
objects have a reddish color and others are gray. {{
 }}

### How big are the Kuiper belt objects?

Scientists consider Pluto to be one of the largest Kuiper belt objects.
It is 2390 km across and is a dwarf planet. The next largest known
Kuiper belt objects are Orcus, 2003 EL61 and 2005 FY9. Orcus is about
1600 km (1,000 miles) across; 2003 EL61 is 70% the size of Pluto and
2005 FY9 is about 50% to 70% of Pluto\'s size.

Recently, scientists found another dwarf planet named Eris that is even
bigger than Pluto. The scientists don\'t know its exact size, but they
think it is about 20% larger than Pluto. At the time it was found, it
was almost 100 times further away from the Sun than the Earth. It can
come about as close to the Sun as Pluto. Eris has a moon named Dysnomia.
The orbit of Eris is tilted almost 45 degrees compared to Earth\'s
orbit. Pluto\'s orbit is only tilted by 17 degrees.

Other large Kuiper belt objects about or over 1000 km across are
Pluto\'s moon Charon, Quaoar, Varuna, Ixion, 1996 TL66, 2002 TX300, 2002
TC302, 2002 UX25 and 2002 AW197. Ceres, the largest **asteroid** in the
asteroid belt, is about 950 km across.

There are many other Kuiper belt objects that are only a few kilometers
or tens of kilometers across.

### How many Kuiper belt objects are there?

Over a thousand Kuiper belt objects had been found by astronomers.
Scientists think that there might be more than seventy thousand large
objects in the Kuiper belt. Even though there are so many objects in the
Kuiper belt, it is very light, weighing between ^1^/~25~ and ^1^/~30~ of
Earth\'s mass.

### What is it named after?

After the first object in the belt other than Pluto and its moon Charon
was spotted from the Mauna Kea Observatory in Hawaii in 1992, the belt
was named after the astronomer Gerard Kuiper. Back in 1951 this
scientist wrote that he thought this belt might exist, but there was no
proof at that time. Other astronomers, including Frederick Leonard,
Kenneth Edgeworth, and Julio Fernandez, also thought that the belt
existed. For this reason some astronomers call it the Edgeworth-Kuiper
belt.

### What are the Kuiper belt objects named after?

When an object is discovered in space, it is given a temporary name
called a \"provisional designation\". This temporary name begins with
the year the object was discovered, followed by some letters and numbers
that tell in what month and in what order it was discovered. Later on,
important objects are given formal names, often taken from mythology.

The Kuiper belt objects Orcus, Charon, and Varuna were all named after
mythological gods of the underworld. Ixion was named after a
mythological person in the underworld. Quaoar was named after a creation
god of the Native American Tongva people.

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