The Kuiper Belt is a disc-shaped region beyond Neptune that extends from 30 to 55 astronomical units from the Sun. It is populated with hundreds of thousands of icy objects larger than 100 km, including the dwarf planet Pluto. The discovery of the Kuiper Belt Object Eris in 1992, which is similar in size to Pluto, led astronomers to reclassify Pluto as a dwarf planet along with Eris. In 2015, NASA's New Horizons spacecraft became the first mission to explore Pluto up close, finding it to be a cold, icy world.

1. Pluto and Kuiper Belt
Roldan S. Pagaduan

2. Kuiper Belt
• The Kuiper Belt is a disc-shaped region beyond
Neptune that extends from about 30 to 55
astronomical units.
• This distant region is probably populated with
hundreds of thousands of icy bodies larger
than 100 km (62 miles) across and an
estimated trillion or more comets.
• Dwarf planet Pluto may be the best known of
the larger objects in the Kuiper Belt.

3. Kuiper Belt

4. Kuiper Belt

5. Kuiper Belt
• The first of these strange bodies, which
astronomers call Kuiper Belt Objects (KBOs),
came to light in 1992, discovered by Dave
Jewitt and Jane Luu.
• Beginning in 1987 they had doggedly scanned
the heavens in search of dim objects beyond
Neptune.
• Jewitt (University of Hawaii) and Luu (UC
Berkeley) wanted to name their find "Smiley,"
but it has since been cataloged as "1992 QB1."

6. Kuiper Belt
• That discovery marked our first glimpse of the
long-sought Kuiper Belt, named after Gerard
Kuiper who, in 1951, proposed that a belt of
icy bodies might lay beyond Neptune.

7. Kuiper Belt
In July 2005, a team of scientists announced
the discovery of a KBO that was initially
thought to be about 10 percent larger than
Pluto. The object, temporarily designated
2003UB313 and later named Eris, orbits the
sun about once every 560 years, its distance
varying from about 38 to 98 AU. Eris has a
small moon named Dysnomia. More recent
measurements show it to be slightly smaller
than Pluto.

8. Kuiper Belt
• The discovery of Eris -- orbiting the sun and
similar in size to Pluto (which was then
designated the ninth planet) -- forced
astronomers to consider whether Eris should
be classified as the tenth planet. Instead, in
2006, the International Astronomical Union
created a new class of objects called dwarf
planets, and placed Pluto, Eris and the
asteroid Ceres in this category.

9. Kuiper Belt
• In 2015, NASA's New Horizons spacecraft flew
past Pluto, making the first up-close
exploration of a Kuiper Belt Object. The
spacecraft is continuing deeper into this
region of icy debris and may be able to
explore at least one more object.

10. Pluto

11. Pluto
• Pluto was discovered in 1930 by Clyde
Tombaugh from the United States.
• Pluto was known as the smallest planet in the
solar system and the ninth planet from the
sun.
• Today, Pluto is called a “dwarf planet.”
• On average, Pluto is more than 3.6 billion
miles (5.8 billion kilometers) away from the
sun.

12. Pluto
• Pluto was named by an 11-year-old girl from
England, Venetia Burney.

13. Pluto
• Pluto has five moons. Its largest moon is
named Charon. Charon is about half the size
of Pluto. Pluto's four other moons are named
Kerberos, Styx, Nix and Hydra.

14. Why Is Pluto Not Called a Planet
Anymore?
• In 2003, an astronomer saw a new object
beyond Pluto. The astronomer thought he had
found a new planet. The object he saw was
larger than Pluto. He named the object Eris.

15. Why Is Pluto Not Called a Planet
Anymore?
• Pluto is also called a plutoid. A plutoid is a
dwarf planet that is farther out in space than
the planet Neptune. The three known plutoids
are Pluto, Eris and Makemake.

16. What Is Pluto Like?
• Pluto is very, very cold. The temperature on
Pluto is 375 to 400 degrees below zero. Pluto
is so far away from Earth that scientists know
very little about what it is like. Pluto is
probably covered with ice.
• Pluto has about one-fifteenth the gravity of
Earth. A person who weighs 100 pounds on
Earth would weigh only 7 pounds on Pluto.

17. What Is Pluto Like?
• Most planets orbit the sun in a near-circle.
The sun is in the center of the circle. But Pluto
does not orbit in a circle! The orbit of Pluto is
shaped like an oval. And the sun is not in the
center. Pluto's orbit is also tilted.

18. Pluto
• In 2006, NASA launched the first mission to
Pluto. It is called New Horizons. New Horizons
is a spacecraft that is going to the edge of the
solar system. The spacecraft is about the size
of a piano. It was a nine-year trip to reach
Pluto. In 2015, New Horizons arrived at Pluto.
The mission will spend more than five months
studying Pluto and its moons. New Horizons
will then study other objects in the Kuiper
Belt.