59 The Outer Solar System-Mid

The Outer Solar System FOCUS Question What exists beyond the planets in the solar system?

Beyond the Planets You may think that once you've passed Neptune, you've left the solar system. But you have a long way to go! The outer solar system is home to the Kuiper (KY-pur) Belt and Oort Cloud. This huge expanse of space contains trillions of comets and other frozen bodies. The Kuiper Belt is a disc-shaped region surrounding the Sun. It is located beyond Neptune's orbit. It is a bit like the Asteroid Belt. Instead of asteroids, it is made up of comets and other interesting space objects. The Oort Cloud is a large region much farther from the Sun than the Kuiper Belt. It is a massive sphere that surrounds the entire solar system.

Solar Leftovers The Kuiper Belt and Oort Cloud contain material left over from the birth of the Sun and solar system. It happened a bit like this: 1 The solar system was formed from the solar nebula—an area of dust and gas. 2 This huge nebula began to pull together (or condense) and swirl forming a disc. 3 Pressure at the disc's center was intense. It was so great that atoms began to combine. This process is called fusion. The Sun was born!

4 The leftover material clumped together here and there. forming larger and larger objects. These objects became the planets. 5 Toward the outer reaches of the solar system. smaller objects remained. They formed the Kuiper Belt and Oort Cloud. Today, the Kuiper Belt and Oort Cloud give us glimpses of what the early solar system was like.

In the Kuiper Belt: Dwarf Planets, Most dwarf planets including Pluto, call the Kuiper Belt home. Pluto was discovered in 1930. At first, it was considered the ninth planet. It is smaller than Earth's moon and has five moons of its own. Then Eris was discovered in 2003. It's nearly the same size as Pluto. Eris doesn't qualify as a planet. Scientists decided to downgrade Pluto to a dwarf planet. Makemake (MAH-kay MAH-kay) and Haumea are also dwarf planets in the Kuiper Belt. Characteristics of a Planet large round orbits a star has an atmosphere the largest object in its orbit by far

In the Kuiper Belt: Comets and Discs Besides dwarf planets, the Kuiper Belt is home to billions of icy comets. These comets are short- period comets. They complete their orbits around the Sun in two hundred years or less. Sometimes overlapping the Kuiper Belt are Scattered Disc objects. These objects are affected by Neptune's powerful gravity. The tug of this gas giant pulls them into unusual orbits. The dwarf planet Eris is a Scattered Disc object. Math Moment Halley's Comet is a famous short- period comet that is visible from Earth about every 75 years. It was last seen in 1986. When will it return?