1. The Planets: An Overview 23.1 The Solar System  The terrestrial planets are planets that are small and rocky—Mercury, Venus, Earth, and Mars.  The Jovian planets are the huge gas giants—Jupiter, Saturn, Uranus, and Neptune.  Pluto does not fit into either the Jovian or the terrestrial category.

2. Orbits of the Planets

3. The Planets: An Overview 23.1 The Solar System  Size is the most obvious difference between the terrestrial and Jovian planets.  Density, chemical makeup, and rate of rotation are other ways in which the two groups of planets differ.

4. Planetary Data

5. 23.1 The Solar System CharacteristicTerrestrial PlanetsJovian Planets Distance from one planet to the next Diameter Density Rotation Rate Atmosphere Composition

6. 23.1 The Solar System CharacteristicTerrestrial PlanetsJovian Planets Distance from one planet to the next orbits are close togetherorbits are far apart Diametersmaller diameterlarger diameter Densitymore denseless dense Rotation Raterotate slower Atmospherethin or no atmospherethick atmosphere Compositioncomposed mostly of rocky and metallic substances, with few gases and ices mostly made of gases and ices, but with rocky and metallic materials in their cores

7. The Planets: An Overview 23.1 The Solar System  The Interiors of the Planets The substances that make up the planets are divided into three groups: gases, rocks, and ices.  The Atmosphere of the Planets The Jovian planets have very thick atmospheres of hydrogen, helium, methane, and ammonia. By contrast, the terrestrial planets, including Earth, have meager atmospheres at best.

8. Scale of the Planets

9. Formation of the Solar System 23.1 The Solar System  Nebular Theory A nebula is a cloud of gas and/or dust in space. According to the nebular theory, the sun and planets formed from a rotating disk of dust and gases.

10. Formation of the Solar System 23.1 The Solar System  Planetesimals Planetesimals are small, irregularly shaped bodies formed by colliding matter.

11. Formation of the Universe

12. Planetary Composition, Distance from the Sun, and Melting Point