THE SOLAR SYSTEM

Solar System Solar System- a star and all the objects orbiting it. Our solar system includes the Sun and all of the planets, dwarf planets, moons, and solar system bodies that revolve around it. Solar system bodies include asteroids, meteoroids, and comets.

Planets Planet- large body orbiting the Sun or other star. Eight planets orbit the Sun in our solar system. In order of increasing distance from the Sun, they are: (1) Mercury, (2) Venus, (3) Earth, (4) Mars, (5) Jupiter, (6) Saturn, (7) Uranus, and (8) Neptune.

Inner Planets Mercury, Venus, Earth, and Mars. These planets are known as the rocky planets because they are similar is size and composition. The rocky planets are made mostly of iron and rock. All the inner planets are solid.

Asteroids and the Asteroid Belt Asteroid - rocky or metallic objects that orbit the Sun. Asteroids are found in a belt between the orbits of Mars and Jupiter. They orbit the Sun just like planets. Astronomers believe that asteroids are material that never combined to become a planet.

Outer Planets Jupiter, Saturn, Uranus, and Neptune These planets are known as the gas giant planets. These four planets share several properties. The gas giant planets are large, rotate rapidly, and have thick gaseous outer layers.

Dwarf Planets Dwarf Planet- round objects with less mass than planets that also orbit the Sun. Unlike a planet, a dwarf planet doesn’t have a strong enough gravitational pull to clear the region of its orbit. The dwarf planet Ceres, for example, orbits in a region of space called the Main Belt between the orbits of Mars and Jupiter. Ceres shares the Main Belt with millions of smaller asteroids.

Dwarf Planets (continued) Other dwarf planets orbit mainly beyond Neptune in a region of space known as the Kuiper Belt. The dwarf planets beyond Neptune are known as plutoids, in honor of Pluto. They share this region with many smaller, icy, comet like bodies. The first Kuiper Belt objects to be called dwarf planets include Pluto and Eris.

Pluto Pluto was once considered to be the smallest, coldest, and furthest planet from the Sun. In 2006, the International Astronomical Union (IAU) made some new "planetary rules.“ According to the new rules, a true planet must do three things: 1. It must orbit the Sun 2. It must be big enough for gravity to make it into a round ball 3. It must have cleared out its orbital neighborhood

Pluto (continued) Pluto follows the first two rules, however, it does not follow rule number three. Pluto’s neighborhood is full of "junk." The Kuiper Belt is close by and it is filled with icy particles. Therefore, Pluto is defined as a dwarf planet.

Moons More than 100 moons, also called satellites, orbit the planets. Moons orbit all the planets except Mercury and Venus. The inner planets have few moons. The giant outer planets have many moons. The giant planets probably have more small moons not yet discovered.

Comets Comet- a ball of ice and rock that orbits the Sun. As the chunks of ice and rock approach the Sun, sunlight begins to warm it. The comet’s ice begins to warm and forms a cloud surrounding the nucleus, or center, of the comet. Pressure from sunlight drives the cloud material away from the nucleus forming the comet’s tail. The tail always points away from the Sun.

Meteoroids, Meteors, and Meteorites meteoroid- Small, rocky objects that orbit the Sun in both the outer and inner regions of the solar system. meteor - A meteoroid that enters the Earth’s atmosphere and burns with a streak of light. meteorite - Any part of a meteoroid that reaches Earth’s surface.

BRAIN POP- SOLAR SYSTEM orer/0410/quickflicks/ orer/0410/quickflicks/