Solar System

The center of the Solar System is the Sun. The Solar System is made up of the Sun and all the planets, asteroids, and other objects that orbit the Sun.

The Planets

There are eight planets in our Solar System. Starting with the closest to the sun they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The closest four planets (Mercury, Venus, Earth, and Mars) are termed terrestrial planets, meaning they have a hard rocky surface. The furthest four planets (Jupiter, Saturn, Uranus, and Neptune) are called gas giants. These planets are much larger and their surface is composed of gas elements (mostly hydrogen).

Other Objects

In addition to the Sun and the eight planets, there are other objects that are part of the Solar System.

• Dwarf planets - Dwarf planets are objects similar to planets in the Solar System, however they are defined as not large enough to have "cleared their orbital region of other objects." Some of the dwarf planets in the Solar System include Pluto, Ceres, Eris, Haumea, and Makemake.
• Comets - Comets are objects made of ice, dust, and rocks that orbit the sun. They often have a visible "tail" of gas that comes from solar radiation and solar wind. Comets originate from the Kuiper belt and the Oort cloud.
• Asteroid belt - The asteroid belt is a region between the planets Mars and Jupiter. In this region thousands of rocky objects orbit the Sun. They range in size from tiny dust like particles to the dwarf planet Ceres.
• Kuiper belt - The Kuiper belt is a region of thousands of small bodies that exists outside the orbit of the planets. Objects in the Kuiper belt consist of "ices" such as ammonia, water, and methane.
• Oort cloud - The Oort cloud exists much further out than the Kuiper belt. Around a thousand times as far away from the Sun. Up to now scientists have only guessed at the existence of the Oort cloud which they think consists of thousands of small icy objects. The Oort cloud is at the very edge of the Solar System.

Milky Way

The Solar System is part of a bigger grouping of stars called a galaxy. Our galaxy is the Milky Way. The Solar System orbits around the center of the Milky Way.

Interesting Facts about the Solar System

• Because Uranus and Neptune contain many "ices" such as water, methane, and ammonia they are often referred to as the "ice giants."
• Scientists estimate there are around 200 billion stars in the Milky Way galaxy.
• Pluto was once considered a full planet, but was redefined as a dwarf planet in 2006.
• About 99.85% of the mass of the Solar System is the Sun. All the other planets, asteroids, moon, etc. together make up less than 0.15% of the Solar System's mass.
• The area around the Sun where the Sun's solar wind has an influence is called the heliosphere.
• All of the planets orbit the Sun in the same counterclockwise direction.
• Scientists who study the solar system and outer space are called astronomers.